Luminous Landscape Forum
Equipment & Techniques => Cameras, Lenses and Shooting gear => Topic started by: ErikKaffehr on December 26, 2015, 08:39:31 am
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Hi,
This question was posted on the MFD threads:
"Is there a reason for the blue/cyan bias on the Sony A7RII images? I have seen it not just in Erik's samples but in many other's as well."
I know that some MFD users now work with Sony A7r, and would be interested to hear about their experience.
Here is my personal opinion:
- White balance is a most important factor in colour reproduction, Sony's AWB may be cooler than other makes.
- Colour profiles are probably more important than sensor characteristics.
- The Alpha 900 was known to have "good colour", but I don't know if that applies to current models. There are some interesting articles discussing this: https://www.onlandscape.co.uk/2013/01/camera-colour-first-tests/
Best regards
Erik
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I never used a MFD and I never use a A7R2.
My opinion is that the A7R2 color filters is really optimized for high signal at the price of color selectivity.
EX: 1ds3 and 5d2 have probabilly the same sensor, but with different color array: the first has better colors, the second lesser noise.
The same things for a5000 (better noise) and X100 (better colors).
I think that most of currents models use less selective filter array for better high iso, noise and dinamic range (and better DXO mark and dpreview).
I buyed (and quickly sold) the D800, but I found that the image quality was a big step back from D700.
An example: with d800 color folliage form different trees is flat and pritty the same, with D700 or 1ds3 is more rich.
With merrils is even richer, but at the price of some random colors.
The D800 DR is great, but colors are flats and full of shifts.
And there isn't a AWB problem: D800 has a good AWB compared to D700.
I think that color reprodution is mostly dependand form:
1) subject lighting
2) camera color filter
3) camera profiling (and photographer color management skills)
the Alpha 900 has a great color reprodution, but very poor high iso performance, that confirm my opinion.
PS:
I'm start to think that an high dxomark (that is only a noise benchmark) rating means poor sensor camera: all my preferred camera are around 80.
The color reprodution is now the most important (and less discuted) factor in a camera:
resolution, noise and dynamic range are now almost goods for all cameras, but color reprodution that is the first thing that we notice in a photo.
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I never used a MFD and I never use a A7R2.
My opinion is that the A7R2 color filters is really optimized for high signal at the price of color selectivity.
EX: 1ds3 and 5d2 have probabilly the same sensor, but with different color array: the first has better colors, the second lesser noise.
The same things for a5000 (better noise) and X100 (better colors).
I think that most of currents models use less selective filter array for better high iso, noise and dinamic range (and better DXO mark and dpreview).
I buyed (and quickly sold) the D800, but I found that the image quality was a big step back from D700.
An example: with d800 color folliage form different trees is flat and pritty the same, with D700 or 1ds3 is more rich.
With merrils is even richer, but at the price of some random colors.
The D800 DR is great, but colors are flats and full of shifts.
And there isn't a AWB problem: D800 has a good AWB compared to D700.
...
PS: I'm start to think that an high dxomark (that is only a noise benchmark) rating means poor sensor camera: all my preferred camera are around 80. The color reprodution is now the most important (and less discuted) factor in a camera: resolution, noise and dynamic range are now almost goods for all cameras, but color reprodution that is the first thing that we notice in a photo.
Interesting thought,
which seems to be basically supported by the Sensitivity Metamerism Index which is reported as well by DxO (see measurements > color response), and which is 78 for the Nikon D800 vs higher 83 for the D700. Likewise with the mentioned Canon 5DII, SMI 80 vs the 1DsIII, SMI 86. But then, the Sony A7RII yields a high SMI of 85 as well.
Although DxO does not seem to be really convinced that the numbers would be meaningful: >> In practice, the SMI for DSLRs ranges between 75 and 85, and is not very discriminating. It is different for low-end cameras (such as camera phones), which typically have a SMI of about 40. For this reason, we give this measurement as an indication but do not integrate it in DxO Mark.<<
http://www.dxomark.com/About/In-depth-measurements/Measurements/Color-sensitivity
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Hi,
The DxO rating is probably most influenced by DR. Not really because it is more important than the other factors, but because a lot of progress has been made in that area.
The SMI is a way to measure how close the FGA (Filter Grid Array) is to Luther Ives condition for a given illuminant. A high SMI means close to Luther Ives. A good description is given here: http://dougkerr.net/Pumpkin/articles/Metameric_Error.pdf
If the spectral response of the FGA/sensor combination is known, the colour separation can be calculated. The image below is shows the colour separation of the Canon 5DII. It shows the Adobe RGB, and Pointer's gamut. Pointer's gamut is essentially all the non specular colours occurring in nature.
(http://www.ludd.luth.se/~torger/img/ssf_csep.png)
Taken from Anders Torger's: http://www.ludd.luth.se/~torger/dcamprof.html
What I essentially want to say is that it is to easy to make assumptions, but reality is more complex.
Anders Torger, the author of DCamProf, takes an interesting approach, he first creates a "neutral tone operator" and than adds a specific look to profile:
http://www.ludd.luth.se/~torger/dcamprof.html#design_look
I also add two images shot at the same time with a Canon 5DIII and a Sony A99, I did not have my A7rII at that time, but I would expect that the A7rII is pretty similar to the A99 in colour rendition. Sony left and Canon right.
Best regards
Erik
Interesting thought,
which seems to be basically supported by the Sensitivity Metamerism Index which is reported as well by DxO (see measurements > color response), and which is 78 for the Nikon D800 vs higher 83 for the D700. Likewise with the mentioned Canon 5DII, SMI 80 vs the 1DsIII, SMI 86. But then, the Sony A7RII yields a high SMI of 85 as well.
Although DxO does not seem to be really convinced that the numbers would be meaningful: >> In practice, the SMI for DSLRs ranges between 75 and 85, and is not very discriminating. It is different for low-end cameras (such as camera phones), which typically have a SMI of about 40. For this reason, we give this measurement as an indication but do not integrate it in DxO Mark.<<
http://www.dxomark.com/About/In-depth-measurements/Measurements/Color-sensitivity
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If the spectral response of the FGA/sensor combination is known, the colour separation can be calculated. The image below is shows the colour separation of the Canon 5DII. It shows the Adobe RGB, and Pointer's gamut. Pointer's gamut is essentially all the non specular colours occurring in nature.
http://www.ludd.luth.se/~torger/img/ssf_csep.png
Taken from Anders Torger's: http://www.ludd.luth.se/~torger/dcamprof.html
What I essentially want to say is that it is to easy to make assumptions, but reality is more complex.
Hi,
I think it basically quite simple:
There is a fundamental antagonism between: a) low noise and b) meeting the Luther-Ives condition,
and the better b) is fulfilled the easier it is for Raw converter like LR/ACR to reconstruct "accurate" color (scene-referred, colorimetric) and finally to derive what is called: good color.
What pdp11 describes above is essentially in line with my experience with LR/ACR and different cameras over the past decade. Some cameras "interact" better with LR/ACR than others in terms of good color which finally means less or more work in post processing (and with dng-profiling, if you want so).
Does it correlate with DxO's simple Sensitivity metamerism index ? You are probably right that we need a more sophisticated measure here, maybe like the u'v' heat map as shown above. But then, I also see some remarkable correlation of DxO's SMI with my empirical rating of my cameras' colors in LR/ACR.
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You are probably right that we need a more sophisticated measure here, maybe like the u'v' heat map as shown above. But then, I also see some remarkable correlation of DxO's SMI with my empirical rating of my cameras' colors in LR/ACR.
Why don't they just measure each channel's relative absolute QE vs wavelength and publish that instead of these milkshake indicators? It can't be that hard to do it professionally if a hobbyist can give it a rough and tumble try for $10 (http://www.strollswithmydog.com/bayer-cfa-spectral-power-distribution/).
Jack
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Jack,
Impressed by your ingenuity…
Best regards
Erik
Why don't they just measure each channel's relative absolute QE vs wavelength and publish that instead of these milkshake indicators? It can't be that hard to do it professionally if a hobbyist can give it a rough and tumble try for $10 (http://www.strollswithmydog.com/bayer-cfa-spectral-power-distribution/).
Jack
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The A7R2 CMOS sensor is Back-Side illuminated, meaning that light does not have to pass through the wiring layer of the chip before being absorbed. Shorter wavelength light is absorbed first in the silicon wafer, red light is absorbed deepest in the sensor. I am guessing that BSI sensors are more efficient in acquiring shorter wavelengths of light than front-side illuminated sensors, and this may produce a bias towards blue/cyan.
PDP-11/35, PDP-11/34... used the latter for image processing. PDP-8, first film scanner. But did much more with the VAX 11/780, 11/750, and 11/730.
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Hi,
Would that be the case, I would think WB and profiling would take care of that.
My guess is that it may be another myth, or it could be that auto WB on Sony's may be a bit on the cold side. As an old Sony user I have found that doing WB on a grey card generally makes the images "warmer" than Sony's WB.
Best regards
Erik
The A7R2 CMOS sensor is Back-Side illuminated, meaning that light does not have to pass through the wiring layer of the chip before being absorbed. Shorter wavelength light is absorbed first in the silicon wafer, red light is absorbed deepest in the sensor. I am guessing that BSI sensors are more efficient in acquiring shorter wavelengths of light than front-side illuminated sensors, and this may produce a bias towards blue/cyan.
PDP-11/35, PDP-11/34... used the latter for image processing. PDP-8, first film scanner. But did much more with the VAX 11/780, 11/750, and 11/730.
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Looking at the spectral response of other Sony BSI sensors, the peaks are shifted towards shorter wavelengths as compared with their Front-Side illuminated sensors. Blue response is increased, red response is decreased. What I would expect given the technology. You can compensate using white balance, which would scale down the Blue channel compared with Red. This is probably where Sony decided to get as many photons as possible out of the sensor and let the user color balance the image later. Easier to decrease channel values after the light has been collected.
http://www.sony.net/Products/SC-HP/new_pro/april_2014/imx214_e.html
There certainly is a blue/cyan shift for the Sony BSI sensor that they actually publish the response curves.
Is the spectral response of the A7R2 sensor a trade secret for Sony? Many sensor manufacturers publish this data.
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Looking at the spectral response of other Sony BSI sensors, the peaks are shifted towards shorter wavelengths as compared with their Front-Side illuminated sensors. Blue response is increased, red response is decreased. What I would expect given the technology. You can compensate using white balance, which would scale down the Blue channel compared with Red. This is probably where Sony decided to get as many photons as possible out of the sensor and let the user color balance the image later. Easier to decrease channel values after the light has been collected.
http://www.sony.net/Products/SC-HP/new_pro/april_2014/imx214_e.html
I am not sure what you are comparing here ?
the URL has the following graph :
(http://www.sony.net/Products/SC-HP/new_pro/april_2014/img/imx214_2.gif)
for 2 sensors : "Solid line: IMX214 Dashed line: IMX135"
and both sensors are BSI : IMX135 = "Back-illuminated process" and IMX214 = "Back-illuminated process + reduced height structure"
so it is BSI vs BSI... not FSI against BSI
plus you forget CFA - whatever difference in silicone in terms of what photones do pass might be totally altered by a different CFA recipe...
plus as people know P1 for example simple reused A7R profile for A7R2 in C1 (P1 does that all the time for dSLRs/dSLMs) ... and profile can totally alter things.
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There certainly is a blue/cyan shift for the Sony BSI sensor that they actually publish the response curves.
Are you referring to Figure 2? Where is the shift in that filterless diagram?
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filterless
you mean sensor w/o IR/UV cut glass on top of it ?
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http://www.vision-systems.com/articles/2011/11/backside-illuminated-image-sensors-optimizing-manufacturing-for-a-sensitivity-payoff.html
(http://www.vision-systems.com/content/dam/VSD/online-articles/2011/11/vsdimecF3112811.gif)
"Quantum efficiencies over the visible spectrum, from bottom to top: (1) FSI imager without microlenses, (2) FSI imager with microlenses, (3) state-of-the-art BSI, (4) BSI from imec with record efficiency."
so you can optimize both ends in visible (range from ~380... ~730 shall cover it) and further alter with CFA and IR/UV cut filters on top of that
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you mean sensor w/o IR/UV cut glass on top of it ?
Right, as used. To indicate a shift one should show sensor1+filters 'unshifted' and sensor2+filters 'shifted'. That does look like a very wide green channel.
Jack
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Compare the BSI spectral response curves with traditional CMOS- Blue response is higher, and in the newer sensor shown- QE numbers for Blue increased, Red decreased.
Seems they are going for increased QE across the spectrum. With the High-ISO performance of cameras being the latest metric for Hot Rodding, seems they will optimize for High ISO. That means maximize QE and minimize the filters in the CFA. True separation filters would cut out 2 stops. No CFA filters comes close to that.
Anyway- BSI technology means placing the photosensitive layers closer to the surface of the chip. Blue light is absorbed close to the surface. The photosensitive portion is now closer to the surface and is more efficient at absorbing blue light. Absorbing light in the in the CFA cuts into the QE of the completed sensor package, means lower ISO performance. You can correct the color balance in post, but leave the photon count in the RAW image. You can always use a color correction filter to warm the image if you don't like what the CFA is doing.
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Yes, with mirrorless there is no reason not to use some filter. Whether a single filter can improve separation is a different question.
My old 1Ds3 is my main camera, trees and shrubs in woods render much more subtly than anything I have seen from the A7R2 but the rez and DR are not in the same class.
Edmund
Compare the BSI spectral response curves with traditional CMOS- Blue response is higher, and in the newer sensor shown- QE numbers for Blue increased, Red decreased.
Seems they are going for increased QE across the spectrum. With the High-ISO performap)nce of cameras being the latest metric for Hot Rodding, seems they will optimize for High ISO. That means maximize QE and minimize the filters in the CFA. True separation filters would cut out 2 stops. No CFA filters comes close to that.
Anyway- BSI technology means placing the photosensitive layers closer to the surface of the chip. Blue light is absorbed close to the surface. The photosensitive portion is now closer to the surface and is more efficient at absorbing blue light. Absorbing light in the in the CFA cuts into the QE of the completed sensor package, means lower ISO performance. You can correct the color balance in post, but leave the photon count in the RAW image. You can always use a color correction filter to warm the image if you don't like what the CFA is doing.
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Compare the BSI spectral response curves with traditional CMOS
sure - please post a link where ?
- Blue response is higher, and in the newer sensor shown- QE numbers for Blue increased, Red decreased.
as other parts of the spectrum (see my link above) - the manufacturer can control what and where will be increased and you again forget to include the effect of 1) CFA 2) IR/UV cut filters 3) camera profiles...
True separation filters would cut out 2 stops.
and the proof link is where ? why 2 and not 1.5 or 2.5 ?
Anyway- BSI technology means placing the photosensitive layers closer to the surface of the chip. Blue light is absorbed close to the surface.
yes and you can design thing with even more increase in "red" part
(http://www.vision-systems.com/content/dam/VSD/online-articles/2011/11/vsdimecF3112811.gif)
so why do you think that Sony didn't increase QE across the spectrum ?
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My old 1Ds3 is my main camera, trees and shrubs in woods render much more subtly than anything I have seen from the A7R2...
You may very well be right, but until someone posts comparable Spectral Response (absolute QE in Kodak lingo) diagrams of the sensors in question as used in those two cameras all we've got to go on are the SMIs, which say the two cameras are comparable. I think there is a lot of room for confusion and misunderstanding (especially on my part:-) where color is concerned. For instance, in order to minimize the green discrimination problem you seem to be having with the a7RII in the woods, which of these two CFAs would you prefer?
(http://i.imgur.com/1xDhd0u.png)
C'mon Edmund, buy you a beer if you play ;)
Jack
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Would that be the case, I would think WB and profiling would take care of that.
My guess is that it may be another myth, or it could be that auto WB on Sony's may be a bit on the cold side. As an old Sony user I have found that doing WB on a grey card generally makes the images "warmer" than Sony's WB.
Ditto. Whatever is the difference, I believe it's deliberate. I'm also a long time Sony user, my first digital camera from them was DSC F717, and my observations match yours.
Not that it's directly related, but their Trinitron (CRT) monitors were quite noticeably "cooler" than pretty much anything else. I remember I was once choosing between a Trinitron-based monitor from Sony, and an iiyama... I had both delivered, and was choosing between the two having them side-by-side. I was... "agonizing" until I displayed an explosion shot on both. WOW. On iiyama, it was an EXPLOSION, I could almost feel the heat! On Sony... well, I just sent it back.
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http://www.sony.net/Products/SC-HP/cx_news_archives/img/pdf/vol_65/imx081_091_111pq.pdf
This Sony publication compares a BSI with a FSI sensor.
The peaks for green and red are shifted towards shorter wavelengths, the blue peak is shifted a little to green. Overall, a "cold shift".
Add it all up, and you get some indication of a color shift in BSI sensors. Of course these curves are RGB, meaning they are with the CFA filter. If Sony published Spectral Response for monochrome sensors, it would be easier to see what is going on inherent to the difference in technology.
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http://www.sony.net/Products/SC-HP/cx_news_archives/img/pdf/vol_65/imx081_091_111pq.pdf
This Sony publication compares a BSI with a FSI sensor.
The peaks for green and red are shifted towards shorter wavelengths, the blue peak is shifted a little to green. Overall, a "cold shift".
Add it all up, and you get some indication of a color shift in BSI sensors. Of course these curves are RGB, meaning they are with the CFA filter. If Sony published Spectral Response for monochrome sensors, it would be easier to see what is going on inherent to the difference in technology.
Brian, nice link, take my challenge above. Which would you prefer for less 'shift', A) or B) ? It's a trick question :)
Let's say the camera produces A) but we'd really like it to produce B). In that case, how much of a difference do you think the tiny changes in Spectral Response in the PDF you linked are going to have on the color of the final image once the data makes it through all the processing necessary to display it?
Jack
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Hi,
I don't see significant differences…
Best regards
Erik
Brian, nice link, take my challenge above. Which would you prefer for less 'shift', A) or B) ? It's a trick question :)
Let's say the camera produces A) but we'd really like it to produce B). In that case, how much of a difference do you think the tiny changes in Spectral Response in the PDF you linked are going to have on the color of the final image once the data makes it through all the processing necessary to display it?
Jack
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Hi,
My take is that 'A' would separate green, yellow and red better, but would not be very subtle. I guess 'B' would be more subtle. I also notice the blue sensivity on L channel in 'B'.
Best regards
Erik
You may very well be right, but until someone posts comparable Spectral Response (absolute QE in Kodak lingo) diagrams of the sensors in question as used in those two cameras all we've got to go on are the SMIs, which say the two cameras are comparable. I think there is a lot of room for confusion and misunderstanding (especially on my part:-) where color is concerned. For instance, in order to minimize the green discrimination problem you seem to be having with the a7RII in the woods, which of these two CFAs would you prefer?
(http://i.imgur.com/1xDhd0u.png)
C'mon Edmund, buy you a beer if you play ;)
Jack
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You may very well be right, but until someone posts comparable Spectral Response (absolute QE in Kodak lingo) diagrams of the sensors in question as used in those two cameras all we've got to go on are the SMIs, which say the two cameras are comparable. I think there is a lot of room for confusion and misunderstanding (especially on my part:-) where color is concerned. For instance, in order to minimize the green discrimination problem you seem to be having with the a7RII in the woods, which of these two CFAs would you prefer?
(http://i.imgur.com/1xDhd0u.png)
C'mon Edmund, buy you a beer if you play ;)
Jack
I prefer "A". I don't like the double peak of the Red channel corrupting the Blue response and would not ever want a CFA with these dyes. It would be easy to start with "A" and produce the "B" response mathematically from the Raw file of "A". Most Blue and Green channels have a double peak, but the secondary peak is in the NIR region, and this can be filtered out using an IR blocking filter.
It is very frustrating to spend a lot of money on a camera and have the manufacturer hold back the actual spectral response data. I prefer my Kodak/OnSemi cameras as I know the spectral response from the data sheets.
As far as the BSI vs FSI plots shown in the Sony link, shifting the peaks by 20nm is going to produce a difference. It can always be corrected in the color balance.
To add: The Red curve in "B" looks similar to the dye used in Canon DSLR's. I would not have expected to see a Red dye with such a strong secondary peak in the Blue region to be used. Why did Canon select this dye?
http://www.maxmax.com/spectral_response.htm
The Red dye used by Kodak has a secondary peak, but it is in the UV and is not an issue.
http://www.onsemi.com/pub_link/Collateral/KAF-18500-D.PDF
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Add it all up, and you get some indication of a color shift in BSI sensors. Of course these curves are RGB, meaning they are with the CFA filter.
we can see a color shift in a specific pair of different sensors (small sensels vs 42mp FF) with CFA (so you can't actually say whether, and which, the shift was because of CFA or not), w/o IR/UV cut (and actual camera has it) filter and w/o color transform (by raw converter using a specific camera profile)...
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we can see a color shift in a specific pair of different sensors (small sensels vs 42mp FF) with CFA (so you can't actually say whether, and which, the shift was because of CFA or not), w/o IR/UV cut (and actual camera has it) filter and w/o color transform (by raw converter using a specific camera profile)...
Obviously the spectral response shown in the Sony publication are done without using an IR blocking filter, the graphs just do not go all the way out to 1.1uM.
Spectral response curves are independent of color transforms and raw converter.
If spectral resonse curves were published for monochrome sensors, then we could differentiate what the effects of the BSI vs FSI technology was.
Until then- yes, BSI sensors are more efficient in absorbing light at shorter wavelengths than are FSI sensors. Most manufacturers are not going to throw away the QE gains in the CFA.
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I prefer "A". I don't like the double peak of the Red channel corrupting the Blue response and would not ever want a CFA with these dyes. It would be easy to start with "A" and produce the "B" response mathematically from the Raw file of "A". Most Blue and Green channels have a double peak, but the secondary peak is in the NIR region, and this can be filtered out using an IR blocking filter.
I think the opposite. The short lambda peak in the "red" channel is the only way to get the correct response to spectral violet.
I remind you that the rho cone cells have two peaks.
Jim
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Erik, I've seen this bias in Lr with AWB engaged. However, if I set the WB to that of the lights (love my Wescott multi-WB LED panels) I get good WB. And, of course, WB to a gray card is fine.
http://blog.kasson.com/?p=12553
Jim
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Until then- yes, BSI sensors are more efficient in absorbing light at shorter wavelengths than are FSI sensors.
with this narrow fact there is no argument.
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Erik, I've seen this bias in Lr with AWB engaged. However, if I set the WB to that of the lights (love my Wescott multi-WB LED panels) I get good WB. And, of course, WB to a gray card is fine.
http://blog.kasson.com/?p=12553
Jim
and then again - in LR/ACR WB depends on dcp profile (as it uses the matrices there)... make a different profile (not resuising Adobe matrices) and you will get a different result of WB operation (not only what is displayed as K/tint in UI)...
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and then again - in LR/ACR WB depends on dcp profile (as it uses the matrices there)... make a different profile (not resuising Adobe matrices) and you will get a different result of WB operation (not only what is displayed as K/tint in UI)...
True enough.
However, I got the same results with ASP"
http://blog.kasson.com/?p=12524
and C1 generic:
http://blog.kasson.com/?p=12573
Jim
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Jack, me not play.
Once you have covered the sensor with a CFA and IR filter, there are three independent issues:
- Luther Ives which determines how the rendering resembles human visison.
- DR after the CFA.
- Filter orthogonality which tells you how ugly or pretty the matrix is, and how good your separation is in practical terms, once you have lost DR to wb and ISO push.
My feeling is that the new Sony slightly suffers from both.
Edmund
True enough.
However, I got the same results with ASP"
http://blog.kasson.com/?p=12524
and C1 generic:
http://blog.kasson.com/?p=12573
Jim
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I prefer "A". I don't like the double peak of the Red channel corrupting the Blue response and would not ever want a CFA with these dyes. It would be easy to start with "A" and produce the "B" response mathematically from the Raw file of "A". Most Blue and Green channels have a double peak, but the secondary peak is in the NIR region, and this can be filtered out using an IR blocking filter.
It is very frustrating to spend a lot of money on a camera and have the manufacturer hold back the actual spectral response data. I prefer my Kodak/OnSemi cameras as I know the spectral response from the data sheets.
As far as the BSI vs FSI plots shown in the Sony link, shifting the peaks by 20nm is going to produce a difference. It can always be corrected in the color balance.
To add: The Red curve in "B" looks similar to the dye used in Canon DSLR's. I would not have expected to see a Red dye with such a strong secondary peak in the Blue region to be used. Why did Canon select this dye?
Perhaps Canon (and Nikon) did because B) is one recent estimate of the photopic response of the cones in the average human eye, as Jim correctly hinted to. Did I forget to mention it was a trick question? :)
Anyways I am definitely out of my depth here and glad to see that real color scientists have joined the party who can jump in to save me when I start sinking : the point I was trying to make is that B) could represent one ideal set of CFA recipes while A) is quite far from that ideal - although on the other hand A) is quite typical of CFAs used in current digital still cameras. The CFA in B) could in theory be used as-is to capture excellent color information, while data collected with CFA A) will require massive transformations before it can be used to display an approximation of the color information from the scene as perceived by the average human.
So given that A) is so far off and requires such mathematically intensive manipulation just to get approximately pleasing color out of it, what will such tiny differences as those shown in the Sony spectral response graphs above mean practically? Very little says Erik. The differences look to me like they could almost be classified as measurement error, so I concur. Don't forget, if two curves are similar (and these seem so to me) what gets recorded in the raw data is proportional to the area under each curve. Once appropriate filters for general photography are in place, how different are those areas? Once white balanced? Once subjected to color transformations? My guess is that there is a lot more play elsewhere in the system which will mask those differences, making them virtually immaterial.
Jack
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Jack, me not play.
Once you have covered the sensor with a CFA and IR filter, there are three independent issues:
- Luther Ives which determines how the rendering resembles human vision.
- DR after the CFA.
- Filter orthogonality which tells you how ugly or pretty the matrix is, and how good your separation is in practical terms, once you have lost DR to wb and ISO push.
My feeling is that the new Sony slightly suffers from both.
Edmund
All work and no play makes Jack a dull boy ;) Ok, so on the work side and for my edification: since we know that the a7RII has good - in fact class-leading - DR after the CFA at 'ISO push' compared to other current advanced DSCs, does it just boil down to the orthogonality of the CFA curves? How does one define orthogonality of the curves? Assuming their shapes are pretty typical would it be related to the position and distance of the three peaks, and their half power bandwidths? If so and since we are at it, how does the human visual system discriminate green so well with the apparent lack of orthogonality in B)? Any help by anyone would be appreciated.
Jack
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Perhaps Canon (and Nikon) did because B) is one recent estimate of the photopic response of the cones in the average human eye, as Jim correctly hinted to. Did I forget to mention it was a trick question? :)
Jack
The eye declares color based on a non-additive process, in which "very simplified explanation" tests which cones respond and which ones don't. Certain cells are inhibited from responding in the presence of certain colors. Like positive and negative voting by groups of cells responding to bands of spectra. I saw a spectral curve of the human eye that was stated to be an RGB response that had the double peak in Red while looking for the response curve that matched "B". Most response curves for the eye do not show this second peak. Overall sensitivity of the eye is much different, with blue response being low. One article stated that only 2% of the cones of the eye are "Blue" cones. This is one reason for using a yellow filter when shooting the sky with B&W.
Having the double peak with a camera using additive color- it's blue contamination in the red channel, like IR contamination on Blue and Green if you don't block IR. I use a deep yellow filter on the M Monochrom for most shots. I like to use an Orange filter (block blue and leave the blue channel sensitive to IR only) on the M8 for color-Infrared, then boost the blue channel and swap Blue and Red in the DNG file header.
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The eye declares color based on a non-additive process, in which "very simplified explanation" tests which cones respond and which ones don't. Certain cells are inhibited from responding in the presence of certain colors. Like positive and negative voting by groups of cells responding to bands of spectra. I saw a spectral curve of the human eye that was stated to be an RGB response that had the double peak in Red. Most response curves for the eye do not show this second peak. Overall sensitivity of the eye is much different, with blue response being low. This is one reason for using a yellow filter when shooting the sky with B&W.
Interesting, Brian. Upon further investigation it seems that the detailed shape of the curves depend on the stage at which one looks at them (absorption, fundamental, intermediate, final). I see that in Wyszeki and Stiles a mild second 'red' cone bump tends to be there in graphs where the y-axis represents 'Spectral Absorption Coefficient' or 'Relative Absorptance'. The y-axis of the bottom graph I posted was labeled 'spectral response' (although in spite of that upon second glance its curves are starting to look suspiciously like color matching functions for the 1931 standard observer). Here are the Stockman & Sharpe cone fundamentals normalized to 1 at each peak from the Color and Vision Research Lab at UCSD (http://www.cvrl.org/), the vertical axis being relative energy. I would assume that the un-normalized version of these curves would need to be weighted by the photopic luminosity curve.
(http://i.imgur.com/CM9r2J0.png)
Having the double peak with a camera using additive color- it's blue contamination in the red channel, like IR contamination on Blue and Green if you don't block IR. One article stated that only 2% of the cones of the eye are "Blue" cones. I use a deep yellow filter on the M Monochrom for most shots. I like to use an Orange filter on the M8 for color-Infrared, then boost the blue channel and swap Blue and Red in the DNG file header.
What strikes me in these graphs is how narrow and separated (orthogonal?) blue is compared to green-red. How much do green cones contribute to our perception of color in normal daylight vision?
And how spread out and close to green the blue curve is in CFAs I have seen measured for a few Nikon and Canon cameras. Is the 'green discrimination' issue mainly a function of the intrusive blue channel?
Jack
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Interesting, Brian. Upon further investigation it seems that the detailed shape of the curves depend on the stage at which one looks at them (absorption, fundamental, intermediate, final). I see that in Wyszeki and Stiles a mild second 'red' cone bump tends to be there in graphs where the y-axis represents 'Spectral Absorption Coefficient' or 'Relative Absorptance'. The y-axis of the bottom graph I posted was labeled 'spectral response' (although in spite of that upon second glance its curves are starting to look suspiciously like color matching functions for the 1931 standard observer). Here are the Stockman & Sharpe cone fundamentals normalized to 1 at each peak from the Color and Vision Research Lab at UCSD (http://www.cvrl.org/), the vertical axis being relative energy. I would assume that the un-normalized version of these curves would need to be weighted by the photopic luminosity curve.
(http://i.imgur.com/CM9r2J0.png)
What strikes me in these graphs is how narrow and separated (orthogonal?) blue is compared to green-red. How much do green cones contribute to our perception of color in normal daylight vision?
And how spread out and close to green the blue curve is in CFAs I have seen measured for a few Nikon and Canon cameras. Is the 'green discrimination' issue mainly a function of the intrusive blue channel?
Whenever someone quotes W&S, you know they're a force to be reckoned with. Well played, Jack.
I remember a meeting with a Kodak Research color scientist at Almaden Research Center. First thing he dds was pull a copy of W&S out of his briefcase and set it on the table. Then we talked.
A little background:
http://blog.kasson.com/?p=12462
The big reason that cameras don't use overlapping red and green filters like the rho and gamma cones is SNR. Takes a lot of subtraction to get from there to, say, Adobe RGB.
Jim
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Interesting, Brian. Upon further investigation it seems that the detailed shape of the curves depend on the stage at which one looks at them (absorption, fundamental, intermediate, final). I see that in Wyszeki and Stiles a mild second 'red' cone bump tends to be there in graphs where the y-axis represents 'Spectral Absorption Coefficient' or 'Relative Absorptance'. The y-axis of the bottom graph I posted was labeled 'spectral response' (although in spite of that upon second glance its curves are starting to look suspiciously like color matching functions for the 1931 standard observer). Here are the Stockman & Sharpe cone fundamentals normalized to 1 at each peak from the Color and Vision Research Lab at UCSD (http://www.cvrl.org/), the vertical axis being relative energy. I would assume that the un-normalized version of these curves would need to be weighted by the photopic luminosity curve.
(http://i.imgur.com/CM9r2J0.png)
These curves would look quite different if weighted by the population of each type of cone.
Jim
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(http://i.imgur.com/CM9r2J0.png)
What strikes me in these graphs is how narrow and separated (orthogonal?) blue is compared to green-red. How much do green cones contribute to our perception of color in normal daylight vision?
The gamma cones contribute a lot to our perception of color. They are one axis of three. The beta cones contribute little to luminance, but a great deal to the opponent color (red/green and blue/yellow) results. We wouldn't have a red/green axis without the gamma cells.
BTW, with a lens that has lousy LoCA, it makes a lot of sense for the eye to put most of the luminance sensing in one part of the spectrum.
Jim
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Hi Jim,
Thanks for posting a good link!
For me, the separation of purplish colours is a bit of a mythical area, and I would guess the L (red) channel sensitivity that Jack mentions may play a role in that.
My guess is that spectral response has very little to do with Sony's spectral characteristics, which are probably the same as on the Phase One Q-250 or the Pentax 645Z, but very much depending on camera profiles. Still, I think that camera white balance plays the uttermost role. Number two suspect is camera DCP profile. There are plenty of those, all implementing a different look, and yes I would guess some are better than others. But, to say better, you need define good.
Best regards
Erik
Whenever someone quotes W&S, you know they're a force to be reckoned with. Well played, Jack.
I remember a meeting with a Kodak Research color scientist at Almaden Research Center. First thing he dds was pull a copy of W&S out of his briefcase and set it on the table. Then we talked.
A little background:
http://blog.kasson.com/?p=12462
The big reason that cameras don't use overlapping red and green filters like the rho and gamma cones is SNR. Takes a lot of subtraction to get from there to, say, Adobe RGB.
Jim
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All work and no play makes Jack a dull boy ;) Ok, so on the work side and for my edification: since we know that the a7RII has good - in fact class-leading - DR after the CFA at 'ISO push' compared to other current advanced DSCs, does it just boil down to the orthogonality of the CFA curves? How does one define orthogonality of the curves? Assuming their shapes are pretty typical would it be related to the position and distance of the three peaks, and their half power bandwidths? If so and since we are at it, how does the human visual system discriminate green so well with the apparent lack of orthogonality in B)? Any help by anyone would be appreciated.
Jack
Jack,
Everyone here is smarter than me these days, and any *scientifically*reasoned debate would require me doing at least one week of reading source material. Also, I don't think most of the issues here are about physiological color, assuming there actually exists one unique average individual. The issues arise because of the desire of using three-filter-Bayer which is a tech decision which will doubtless go the way of the 78rpm record in due course.
If you actually want to discuss Bayer camera color, then concerning DR, greenery will absorb most of the reds (chlorophyll) and if you are already standing under a forest canopy under a blue or white sky high CT sky as illumination there will simply not be a lot of red signal for discrimination. Instead of trying to show the world how dumb I am, why don't you use the spectral and camera data you have at your fingertips and a Raw image to see how much actual red light is left and what the data looks like before in-camera multipliers are applied? My guess is that most of the "real" red signal is lost in the noise, although camera "R" whose filter probably looks orange will register a decent reading.
Sony had a camera with decent landscape color, I think it was the A950 or something, it did badly commercially because the filters cut down the ISO too strongly, but may have been the best landscape SLR of recent times.
One can see this game being played in churches - go to a medieval european church and it will be dark and the stained glass will make you swoon - go to a modern church and a lot more light gets in the windows, which convey little emotion.
Edmund
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These curves would look quite different if weighted by the population of each type of cone.
Ah, is that built into the luminosity function? And would you simply multiply the curves above by V(lambda) before normalization in order to obtain what the human visual system measures?
The gamma cones contribute a lot to our perception of color. They are one axis of three. The beta cones contribute little to luminance, but a great deal to the opponent color (red/green and blue/yellow) results. We wouldn't have a red/green axis without the gamma cells.
BTW, with a lens that has lousy LoCA, it makes a lot of sense for the eye to put most of the luminance sensing in one part of the spectrum.
Jim
Makes sense, thanks Jim. So what's your take on the a7RII's color discrimination compared to others out there?
Jack
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Jack,
Everyone here is smarter than me these days, and any *scientifically*reasoned debate would require me doing at least one week of reading source material. Also, I don't think most of the issues here are about physiological color, assuming there actually exists one unique average individual. The issues arise because of the desire of using three-filter-Bayer which is a tech decision which will doubtless go the way of the 78rpm record in due course.
If you actually want to discuss Bayer camera color, then concerning DR, greenery will absorb most of the reds (chlorophyll) and if you are already standing under a forest canopy under a blue or white sky high CT sky as illumination there will simply not be a lot of red signal for discrimination. Instead of trying to show the world how dumb I am, why don't you use the spectral and camera data you have at your fingertips and a Raw image to see how much actual red light is left and what the data looks like before in-camera multipliers are applied? My guess is that most of the "real" red signal is lost in the noise, although camera "R" whose filter probably looks orange will register a decent reading.
Sony had a camera with decent landscape color, I think it was the A950 or something, it did badly commercially because the filters cut down the ISO too strongly, but may have been the best landscape SLR of recent times.
One can see this game being played in churches - go to a medieval european church and it will be dark and the stained glass will make you swoon - go to a modern church and a lot more light gets in the windows, which convey little emotion.
Edmund
Edmund, I mean all this in jest, as a playful learning opportunity. I apologize in advance if my questioning style came across as trying to demonstrate anything other than I do not know how one goes about figuring out if a camera has good color discrimination or not. So when you mention that the A950's filters 'cut down the ISO too strongly' do you mean that the normalized individual channel curves have narrower bandwidths compared to newer designs? Here for instance are the cone sensitivity curves above (dashed lines) resized to the same height and shown on top of the CFA curves from the sensor in the paper linked by Brian, which is used in the M9 I understand (solid lines)
(http://i.imgur.com/iLWi5A5.png)
Is discrimination here all about slimming down and shifting left that big fat blue?
Jack
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True enough.
However, I got the same results with ASP"
http://blog.kasson.com/?p=12524
and C1 generic:
http://blog.kasson.com/?p=12573
Jim
you mean same results for greyscale patches when you set WB using one of them in both converters...
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you mean same results for greyscale patches when you set WB using one of them in both converters...
No, I meant no systematic cyan cast to the other patches after the image was WB'd to one of the neutral patches.
Jim
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With regard to the spectral response curves in the Sony links that I posted: I expect a manufacturer to post manufacturers specifications for the product and not some randomly chosen unit. Numbers given should be representative of production with published numbers for tolerances and variations. The spectral curves given should be for the average production sensor. Kodak, OnSemi, and other manufacturers that target the scientific and technical market tend to publish these numbers. Typical, minimum, and maximum values are in the spec sheet for a given product. Some samples are better than others, and cherry-picking the best of the best usually yields better performance. The KAF-18500 (sensor in the Leica M9) specs indicate a nominal 1.8% red/green and green/blue hue shift, and the note in the spec states that this parameter is measured for every sensor during production testing. The spec also states a Max shift of 12%- hopefully those go into the "engineering samples". If QE peaks really wandered around by as much as 20nm, each sensor would have to be carefully calibrated to yield consistent colors. I believe the spec is much tighter. I used to measure such things, a very long time ago. Multi-Spectral digital imagers, 1980s.
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With regard to the spectral response curves in the Sony links that I posted: I expect a manufacturer to post manufacturers specifications for the product and not some randomly chosen unit. Numbers given should be representative of production with published numbers for tolerances and variations. The spectral curves given should be for the average production sensor. Kodak, OnSemi, and other manufacturers that target the scientific and technical market tend to publish these numbers. Typical, minimum, and maximum values are in the spec sheet for a given product. Some samples are better than others, and cherry-picking the best of the best usually yields better performance. The KAF-18500 (sensor in the Leica M9) specs indicate a nominal 1.8% red/green and green/blue hue shift, and the note in the spec states that this parameter is measured for every sensor during production testing. The spec also states a Max shift of 12%- hopefully those go into the "engineering samples". If QE peaks really wandered around by as much as 20nm, each sensor would have to be carefully calibrated to yield consistent colors. I believe the spec is much tighter. I used to measure such things, a very long time ago. Multi-Spectral digital imagers, 1980s.
Brian,
Too many of us here are now dinosaurs, with knowledge of what went on before, but little knowledge of what is done now in the industry.
One of the differences between cheap and pricey camera product lines is how much calibration and testing goes into individual product samples. I believe it is usual to test in order to establish/confirm parameters for the whole production batch of a sensor.
Dietmar Wueller's Image Engineering make a gadget that spits out a spectral sensitivity curve from one camera click - and computes an ICC profile. The first version of this was based on a slide projector with a stabilised power supply and a bunch of narrowband filters, and needed several clicks. As you know one can also aim a monochromator at the camera and get the same result, this is done at universities routinely, and some do it at home. Jack Holm when he was at at HP had a patent on an active colorchecker thingy based on a collection of LEDs, I'm sure one could make one of those at home too.
I think we could have an effective and productive discussion of what is going on with current cameras, if we chose to get around the showoff factor, and made an effort to get some hard data. As I said before this means collecting real *experimental* spectral curve data, agreeing on some measure of how bad a given Luther-Ives failure is, and validating this metric with real world setting descriptions like "under forest canopy" or "2700K incandescent", and the spectral and S/N data of known cameras AND SCENES.
Any discussion without agreed observer functions, knowledge of how people evaluate scenes, scene measurements, and hard camera data is IMHO a waste of our times; in fact I am sure that if you ask a quadrichromat human she will laugh at your evaluations - but is she representative?
Edmund
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Brian,
Too many of us here are now dinosaurs, with knowledge of what went on before, but little knowledge of what is done now in the industry.
Edmund
I work in the scientific/technical field, manufacturers that cater to that market publish data sheets that are representative of actual sensor performance. It's different from consumer grade sensors. CCD's are still used, the last camera chosen was based on the increased response in the near IR- as per the spectral response curve given by the manufacturer.
https://www.hamamatsu.com/us/en/C3077-80.html
Compare the response with the monochrome Nikon microscope camera that uses the same sensor in the Df. The Nikon was rejected due to poor performance in the NIR.
http://www.nikon.com/products/instruments/lineup/bioscience/camera_microscopy/dsqi2/index.htm
The spectral response curve gives a very good indication as to the performance of a detector. Detector geometry and chemistry affect spectral response. BSI changes the geometry and more blue light will be absorbed at the photosensitive portion of the detector.
A monochrome BSI sensor aimed at the scientific/technical market should have some good spectral response data available, should make it easier to compare the new technology with FSI sensors. I suspect that BSI sensors will have increased response at the short end of the spectrum. It will have very poor IR response. Good for photography, not so good for NIR applications.
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I enjoy threads like this even if I don't follow all of the tech. I wanted to comment on the way FSI chips are made. I may be mistaken but I think there are assumptions that the light has to pass through some silicon on the way to the detector (which would mean absorption of blue more than green, then red. In fact the wiring layers above the sensor surface are suspended in silicon oxide. The oxide will most likely be fluorine or carbon doped to reduce the capacitance between metal lines that run close to each other. Of course there will still be some light absorption and scatter, but nothing like having to pass through silicon, and I don't know the spectral qualities of these oxides to know if blue is affected more. On top of the last oxide layer before the CFA there will be a silicon nitride passivation layer to seal the surface from moisture and although the RI is higher than oxide it will be relatively thin.
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I looked it up- a layer of silicon dioxide (SiO2) is used. Slightly better transmission at longer wavelengths.
I also found some papers on a hybrid CCD/CMOS sensor aimed at better Near Infrared response.
Some articles state that thinned sensors offer higher QE in the visible band at the expense of longer wavelengths. Thicker photo-sensitive sites are subject to recombination, loss of signal. QE peaks shift to shorter wavelengths as the photosensitive layer is thinned. IR response is reduced, which is considered an advantage for photography.
This company gave some numbers for absorption of light as it passes through silicon. I did not realize the difference in penetration depth varied to this degree. I worked with Midwave and Longwave IR, 3um~5um and 9um~12um for the most part, Visible+NIR CCD's.
http://www.aphesa.com/documents.php?class=wp
"Spectral Response of Silicon Sensors" available for download.
Two datasheets for devices from the same family- both CCD's with 100% fill-factor. The shift in QE towards shorter wavelengths (and reducing NIR) and some of the work that went into achieving the results is documented:
http://www.astrosurf.com/audine/pdf/kaf1600.pdf
http://www.onsemi.com/pub_link/Collateral/KAF-1603-D.PDF
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I think the FSI issues stem from the fact that the various orthogonal flow Al metal signal paths on top block light from reaching the gate which is below them. The sensel looks like a funnel. BSI has the added advantage that one can grab signals from the middle of the chip rather than the edges, allowing higher throughput.
I think a color discussion that went somewhere would be useful, because we could turn it into sensor validation code.
Edmund
I enjoy threads like this even if I don't follow all of the tech. I wanted to comment on the way FSI chips are made. I may be mistaken but I think there are assumptions that the light has to pass through some silicon on the way to the detector (which would mean absorption of blue more than green, then red. In fact the wiring layers above the sensor surface are suspended in silicon oxide. The oxide will most likely be fluorine or carbon doped to reduce the capacitance between metal lines that run close to each other. Of course there will still be some light absorption and scatter, but nothing like having to pass through silicon, and I don't know the spectral qualities of these oxides to know if blue is affected more. On top of the last oxide layer before the CFA there will be a silicon nitride passivation layer to seal the surface from moisture and although the RI is higher than oxide it will be relatively thin.
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Agreed that the biggest gain in BSI vs FSI is the angle of acceptance, being able to use large aperture lenses and mounts with short registers. I'm waiting for Leica to put one into the M-Mount camera.
The original question was in regard to a color bias. I used a set of Nikon color filters ranging from Blue through to deep Red arranged on a backlit Slide Sorter to compare the M Monochrom with the DCS200 (KAF-1600). Nikon publishes the response curves for the filters, but that is not as important for detecting a difference between two cameras. I like the slide sorter as the light source is behind the filters. Such an arrangement should be useful for comparing two cameras and testing if the new camera has a bias towards Blue. Look at Raw RGB values from cropped areas within the color filters, compare histograms between the two cameras. Color filters are dirt cheap these days, as are slide sorters. It would also be interesting to put a graduated grey scale card up on a copy stand to test differences between two cameras. Again- easy DIY projects to do at home, cheap.
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Imaging Resource test (http://www.imaging-resource.com/PRODS/sony-a7r-ii/sony-a7r-iiA5.HTM) shows that
Like many cameras, the Sony A7R II shifts cyan toward blue, red toward orange, orange toward yellow and yellow toward green, but shifts are relatively minor. (The cyan to blue shift is actually fairly minor and very common among the digital cameras we test; we think it's a deliberate choice by camera engineers to produce better-looking sky colors. The yellow to green shift combined with its desaturation is however unfortunate, as it can produce somewhat dingy-looking yellows.) With an average "delta-C" color error of 5.45 after correction for saturation at base ISO, overall hue accuracy is about average, with accuracy only varying slightly at higher ISOs.
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Like many cameras, the Sony A7R II shifts cyan toward blue, red toward orange, orange toward yellow and yellow toward green, but shifts are relatively minor. (The cyan to blue shift is actually fairly minor and very common among the digital cameras we test; we think it's a deliberate choice by camera engineers to produce better-looking sky colors. The yellow to green shift combined with its desaturation is however unfortunate, as it can produce somewhat dingy-looking yellows.) With an average "delta-C" color error of 5.45 after correction for saturation at base ISO, overall hue accuracy is about average, with accuracy only varying slightly at higher ISOs.
again this just reflects a specific raw conversion with specific profile... change that and you will get different results... average delta-c = "5.45" ?
http://1.bp.blogspot.com/-H3-8D5Sdd5k/VoLFnxGMtJI/AAAAAAAAKf4/xV6N5zJbc6A/s1600/ACR20151229-01.jpg (http://1.bp.blogspot.com/-H3-8D5Sdd5k/VoLFnxGMtJI/AAAAAAAAKf4/xV6N5zJbc6A/s1600/ACR20151229-01.jpg)
(http://1.bp.blogspot.com/-H3-8D5Sdd5k/VoLFnxGMtJI/AAAAAAAAKf4/xV6N5zJbc6A/s1600/ACR20151229-01.jpg)
little modded Adobe Standard and adding some red primary saturation (+20) in ACR with raw file from I-R and CC24 Classic measurements (30 samples from BabelCOlor)... process 2010 naturally
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Hi,
I am not sure that manufacturers tweak CFA-s a lot to improve high ISO, it can happen from time, but the only way to know is to see the actual curves.
Now, getting back to the Alpha 950, that camera did not even exist, but I am pretty sure that the A900 was meant. And yes, it was known to have good colour. And that was confirmed by some folks I am aware of, namely Tim Parkin, the publisher of On Landscape and Iliah Borg of LibRaw and RawDigger fame.
I have three interesting cameras in context, so I could make a decent test. Something along these lines:
- Build a daylight emulator and an A-illuminant simulator
- Make very good shots of a ColorChecker Passport, avoid surround light and glare with all three cameras
- Build DCP profiles for each
- Now find an adequate target and shoot carefully under constant and repeatable conditions - somewhat problematic for a guy like me who shoots landscapes mostly - include a white balance card or ColorChecker in all shots
- Develop all images with identical setting, using the DCP profiles we generated for each camera
- Do an objective evaluation of colour
[/list
The last point is a bit tricky, unless we shoot test charts.
A year ago I did a comparison between my P45+ and my Sony Alpha 99, in part related to a discussion between me and Tim Parkin. Tim deeply dislikes the colour rendition of the P45+ while he likes that of Sony Alpha 900. What I wanted to see was to what extent raw converter profiles affected colour rendition.
For this comparison a flower with bluish purple petals was chosen. The reason was Tim stated that reproduction of chlorophyll was yellowish on the P45+ and I have previously observed that purples were problematic to reproduce.
I also used my ColorMunki to sample both the bluish purples and the blade greens, so I have a good colour reference.
Here is a link to that comparison: http://echophoto.dnsalias.net/ekr/Articles/OLS_OnColor/SimpleCase/
My surprise was that my P45+ produced nice bluish purple with Lightroom - almost identical to the measured samples - while Capture turned the petals into blue. With the Sony Alpha 99 the situation was pretty similar - Capture One turned bluish purple into blue. This really strengthens my conviction that colour profiles play a greater role than camera CFA:s.
When looking at my measured patches I have noticed that both blade and petal had extremely high infrared content. The ColourChecker patches don't have excessive IR. I guess that IR filtering on the sensor may play a role, as IR affects the red channel. We know that nature greens reflect a lot of IR, light vegetation is one of the characteristics of IR images.
Profiles also twist hues, based on luminosity, here is an article describing it: http://chromasoft.blogspot.se/2009/02/visualizing-dng-camera-profiles-part-3.html
Sandy McGuffog, the author of the above article has a command line tool to modify the way the dcp-profiles handle these twists.
Just to say, I have checked my Adobe Standard Profiles for colour shifts with varying exposure, and they are there. Sandy's tools can sanitise that, but I have not seen any real issue in my work.
Best regards
Erik
Edmund, I mean all this in jest, as a playful learning opportunity. I apologize in advance if my questioning style came across as trying to demonstrate anything other than I do not know how one goes about figuring out if a camera has good color discrimination or not. So when you mention that the A950's filters 'cut down the ISO too strongly' do you mean that the normalized individual channel curves have narrower bandwidths compared to newer designs? Here for instance are the cone sensitivity curves above (dashed lines) resized to the same height and shown on top of the CFA curves from the sensor in the paper linked by Brian, which is used in the M9 I understand (solid lines)
(http://i.imgur.com/iLWi5A5.png)
Is discrimination here all about slimming down and shifting left that big fat blue?
Jack
[/list]
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That would be an interesting test, Erik. I would be interested to hear what Anders Torger thinks about all this...
Jack
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Hi Jack,
I am doing some preparation for this, like getting Solux bulbs and a regulated voltage power supply. Unfortunately I lost my ColorChecker Passport, so I need to order a new one.
I want to make a profile for my Sony A7rII, so looking into the other cameras is not a lot of work.
The cameras I have right now is the A900, a P45+ and the A7rII. For completeness I also have a Minolta Dimage 7D and Sony A99 and Sony A77, I plan to sell those.
Problem is the evaluation part. Technically it is easy, just shoot an IT-8 chart, but doing subjective evaluations is not easy.
Best regards
Erik
That would be an interesting test, Erik. I would be interested to hear what Anders Torger thinks about all this...
Jack
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I want to make a profile for my Sony A7rII
I modded the new from 9.0.2 version IQ3-100 flash - flat art repro profile (replaced the original input curves inside to boost shadows) from C1 distribution and it actually looks nice for A7RII raws