Pages: 1 ... 11 12 [13] 14 15 ... 17   Go Down

Author Topic: DSLR testing sites like DXOmark and Imaging Resource use HMI and LEDs for color  (Read 55953 times)

WayneLarmon

  • Full Member
  • ***
  • Offline Offline
  • Posts: 162

> Membership seems to be required to access the papers.
http://www.cipa.jp/std/documents/e/DC-004_EN.pdf page 19.

Thank you.  For simulating daylight they list using Hoya LB-120 (in front of 3200k tungsten) which isn't available at B&H.  I have some Rosco #3202 CTB



Is that close enough?  (I have a Variac for adjusting a tungsten bulb.  And, of course, ColorMeter for reading CCT.)  I don't have a spot luminance meter so I need to get one. 

I'm not sure where to get an IEC 1146-1 Test chart No. 1 or an ITE Grayscale Chart II.

With said, I'm not sure exactly what is being measured.

Quote
> the existing metrics of evaluating light

... are not for photography. Sensor measures light differently from how we perceive it. Sensor / Film metameric error is not accounted for in those metrics.

Yes, this has been covered extensively earlier in this thread.  I'm aware of the issues.

Quote
> light that renders color well for human eyes also renders light better for cameras.

Hm... Some cameras, like Nikon D3..D5 series, are optimized for artificial light common at sports venues. It's a complex process, that optimization, causing a rather significant deviation from L-I condition to present not the colours that we see under that artificial light but rather the colours we would see if the light would be closer to daylight.

Which is why I asked whether Anders Torgers' DCamProf and/or Lumariver Profile Designer would be helpful.  Both seemed to be received well on LuLa forums.

Quote
> while I've been researching during the course of this thread

I think systematic study starts with textbooks on colour science.

I've already posted that I've reread

Color Management for Photographers: Hands on Techniques for Photoshop Users

Real World Color Management

Billmeyer and Saltzman's Principles of Color Technology 2nd edition

Color Science: Concepts and Methods, Quantitative Data and Formulae 2nd Edition (selectively.)

during the course of this thread, along with spidering external references (such as Jim's blog posts) that were posted.   Alexey recommended Measuring Colour but I've been hoping to find a used copy for less than ~$90.

Anders extensively tested light sources for camera profiling and found even the best LEDs (including Yuji) might not be an improvement over CFLs. (He recommended using Solux bulbs carefully)  But Alexey is working on a Yuji COB for Spectron.  Are there different criteria for camera profiling and for what Spectron is designed to measure?
Logged

Iliah

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 770

> For simulating daylight they list using Hoya LB-120 (in front of 3200k tungsten) which isn't available at B&H.  I have some Rosco #3202 CTB Is that close enough?

No, and Rosco filters are not manufactured to the tolerances needed.

> Anders extensively tested light sources for camera profiling and found even the best LEDs (including Yuji) might not be an improvement over CFLs. But Alexey is working on a Yuji COB for Spectron

Our profiling with Spectron is spectrum-based, using a monochromator. LEDs are not used to illuminate the target is such setups, there is no target present at all. All that is needed is a constant spectrum power distribution (something that you can't achieve with SoLux) and a good coverage of all wavelengths. There is a reason why light sources for monochromators are so expensive. We are making a much cheaper and better suited for photographical purposes one. Shooting targets is a very unreliable profiling method, prone to all kinds of problems with flare, uneven illumination, uneven "white balance", etc. No serious setup should use target shooting (yes, it is much better than nothing, but a guaranteed setup needs very stable set of four high-grade studio flash units and a lot of additional equipment, making the whole thing economically inefficient), and in fact in many cases target shooting is already replaced with spectral profiling. Transition started 15+ years ago.
Logged

Alexey.Danilchenko

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 257
    • Spectron


Anders extensively tested light sources for camera profiling

To be honest nothing on that link suggests Anders actually tested all of the lights. He also explicitly states he has not used them all and simply considered their respective SPD and decided to stay with filtered tungsten halogen. It also quite specifically indicated he had not considered LEDs (due to their "bumpy spectrum"), not even Yuji. So in reality no practical testing has been done to draw any conclusions.
« Last Edit: June 19, 2018, 07:16:32 am by Alexey.Danilchenko »
Logged

WayneLarmon

  • Full Member
  • ***
  • Offline Offline
  • Posts: 162

We are making a much cheaper and better suited for photographical purposes one.

Bearing in mind that the standard for "photographical purposes" on this thread is being able to buy it at B&H, it looks like you have a ways to go. :)

That aside, I'd like to see your project succeed.  If, as you say, that evaluating light spectrums and profiling cameras is mostly futile.  I think that I can manage building one.   There are a lot of pieces in the project.  I was planning on starting by experimenting with a Particle Photon to calibrate myself on managing this particular microcontroller.

I'm guessing that a lot of the rest of the project is in flux while Alexey finishes the COB project, correct?

« Last Edit: June 23, 2018, 12:56:04 pm by WayneLarmon »
Logged

Iliah

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 770

Bearing in mind that the standard for "photographical purposes" on this thread is being able to buy it at B&H, it looks like you have a ways to go. :)

That aside, I'd like to see your project succeed.  If, as you say, that evaluating light spectrums and profiling cameras is mostly futile.  I think that I can manage building one.   There are a lot of pieces in the project.  I was planning on starting by experimenting with a Particle Photon to calibrate myself on managing this particular microcontroller.

I'm guessing that a lot of the rest of the project is in flux while Alexey finishes the COB project, correct?

The idea is to share what we know and thoroughly tested, to provide some help and reliable reference (schematics, PCB design, etc) to those who may need it; and of course to make it reasonably easy for DIY and not overly expensive (comparable or cheaper than the regular profiling setup). The method by itself is not a unique and a very logical one, it became a relative commonplace in 2009. Far from being the first, in 2006 I used off-the-shelf equipment (monochromator, integrating sphere, spectrometer, and light source) for this (because I can afford the expense). Resulting colour transforms were incorporated in RPP about the same time.

LEDs are the best solution that we found (for multiple reasons, including being DIY-friendly), but halogen lamps and xenon flashlamps in strobe mode were also tested to work well. As to COBs, we don't expect any surprises with the recent designs we tried, so it is mostly a matter of testing reliability now, and it takes time. One can come up with his own design, so I don't see how what we are doing in terms of light source design is holding things off for those who are comfortable with EE ;)

B&H: they sell some of our software, I don't see why they wouldn't be interested in selling hardware for spectral profiling in some future. It may be based on this project, or on some other, including by a different team. If one needs to profile lens+camera combos, creating multiple profiles, he may be interested to have it available. But mostly it is about renting and service.
Logged

WayneLarmon

  • Full Member
  • ***
  • Offline Offline
  • Posts: 162

... is holding things off for those who are comfortable with EE ;)

"comfortable with EE" will probably considerably reduce the pool of photographers that would benefit.   I'd like to increase the pool size.  To at least include me.

The Particle Photon part is probably the easiest part of the project (to implement, not to design!)  I looked at the PP code and I'm impressed with the clarity and professionalism.  (Much better than any of my own code.)  The Particle Photon documentation indicates that flashing the firmware should be easy.  After getting the build environment set up and doing the "Hello world" thing, it looks like all the user needs to do with the code is transcribe the calibration data for his/her own Hamamatsu sensor for the "#define CALIBRATION_15F00163" statement.

Based on my reading several issues of Make magazine, probably getting the PCBs made will be even easier (similar to having photo prints made by a printing service.)

Sourcing components isn't difficult--just tedious.  But soldering surface mount components is difficult.  I've never done it myself but I think I can persuade somebody I know to show me how.   Ditto with fabricating COB mounting plates and heatsinks.

A good next step for the project would be to separate the easy-but-tedious portions from the difficult-no-matter-what portions.  With the goal of encapsulating and reducing the latter.  And (big gulp) make it understandable to non-EE photographers.

Any sufficiently advanced technology is indistinguishable from magic.
Clarke's third law

Please make it a bit less magical.
« Last Edit: June 23, 2018, 04:58:59 pm by WayneLarmon »
Logged

Iliah

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 770

"comfortable with EE" will probably considerably reduce the pool of photographers that would benefit.   I'd like to increase the pool size.  To at least include me.

The Particle Photon part is probably the easiest part of the project (to implement, not to design!)  I looked at the PP code and I'm impressed with the clarity and professionalism.  (Much better than any of my own code.)  The Particle Photon documentation indicates that flashing the firmware should be easy.  After getting the build environment set up and doing the "Hello world" thing, it looks like all the user needs to do with the code is transcribe the calibration data for his/her own Hamamatsu sensor for the "#define CALIBRATION_15F00163" statement.

Based on my reading several issues of Make magazine, probably getting the PCBs made will be even easier (similar to having photo prints made by a printing service.)

Sourcing components isn't difficult--just tedious.  But soldering surface mount components is difficult.  I've never done it myself but I think I can persuade somebody I know to show me how.   Ditto with fabricating COB mounting plates and heatsinks.

A good next step for the project would be to separate the easy-but-tedious portions from the difficult-no-matter-what portions.  With the goal of encapsulating and reducing the latter.  And (big gulp) make it understandable to non-EE photographers.

Any sufficiently advanced technology is indistinguishable from magic.
Clarke's third law

Please make it a bit less magical.

If you are going to use SMT components, an excellent video instruction is https://youtu.be/M0wI-5YZQm4 (other Marc's videos on his channel, too). He shows different tools and explains what each is used for, and how to operate it. Equipment varies, technique stays the same. The secret to good and reliable soldering is understanding and feeling the surface tension, it does all the job, even small component alignment. You may want to use some SMT training boards.

Some PCB  manufacturing services also offer the assembly.

Sourcing components is a matter of a shopping list.

Not sure I understand what exactly you mean by "easy-but-tedious portions" and "difficult-no-matter-what portions".
Logged

WayneLarmon

  • Full Member
  • ***
  • Offline Offline
  • Posts: 162

Not sure I understand what exactly you mean by "easy-but-tedious portions" and "difficult-no-matter-what portions".

"Easy-but-tedious" would be going through all the steps that are required for things like flashing the Particle Photons.  And figuring out where to buy all the components and having the PCBs made.  It is easy (but maybe tedious) to write a tutorial to walk people through doing this.  (People don't need to learn everything there is to know about Particle Protons to just flash the firmware with the software you have already written.  A tutorial makes the process easier.)

Easy-but-tedious can be explained with a digestible tutorial.

"Difficult-no-matter-what" is reading schematics and populating the PCBs with SMT components and fabricating aluminum parts for the COBs.  And EE.  These are more like ten-thousand-hour rule things.   

An example of difficult-no-matter-what is playing an advanced musical piece.  There is no way to write a digestible tutorial.  But an advanced musical piece can be encapsulated (with a recording.)

I believe that you have explained that evaluating the color rendering ability of light sources and shooting targets for profiling cameras are both very problematic and that spectral profiling is a much better approach for photographers that want to accurately capture color.  If my interpretation is correct, then I want make an effort to make spectral profiling be more accessible.  If possible.
Logged

Iliah

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 770

> "Difficult-no-matter-what" is reading schematics and populating the PCBs with SMT components

But as I said, the populating of PCBs can be outsourced.

> An example of difficult-no-matter-what is playing an advanced musical piece.

Populating PCBs for Spectron and light sources is nowhere near playing an advanced musical piece, those PCBs are intentionally designed to be cheap and simple to solder and use.

Logged

WayneLarmon

  • Full Member
  • ***
  • Offline Offline
  • Posts: 162

Populating PCBs for Spectron and light sources is nowhere near playing an advanced musical piece, those PCBs are intentionally designed to be cheap and simple to solder and use.

OK, I'll have to wait until I have everything in front of me.

My copy of Hunt and Pointer's Measuring Color just arrived.  Quickly skimming through it, what you have been talking about makes a lot more sense.  None of the other color science books I described earlier covered any of this (what is covered starting in chapter nine of Measuring Color.)  The applied science portions of the older books were more about training chemists how to choose pigments so that plastic buttons matched sweater fabrics.   It was difficult to extrapolate that into spectral profiling of cameras.

Sometimes it is difficult to reduce unknown unknowns to known unknowns.
« Last Edit: June 24, 2018, 09:29:02 am by WayneLarmon »
Logged

Alexey.Danilchenko

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 257
    • Spectron

The Particle Photon documentation indicates that flashing the firmware should be easy.  After getting the build environment set up and doing the "Hello world" thing, it looks like all the user needs to do with the code is transcribe the calibration data for his/her own Hamamatsu sensor for the "#define CALIBRATION_15F00163" statement.

Flashing is easy and can be done from any build environment, including Particle's online web IDE.

The calibration data is stored in an array internally but because it needs to be passed to controlling software as well, initialisation is done as a string from a single sysdef which you can override with your data. The future versions will include a changeable calibration data to allow updating it fro outside (following a spectrometer calibration externally).

But soldering surface mount components is difficult.  I've never done it myself but I think I can persuade somebody I know to show me how.   Ditto with fabricating COB mounting plates and heatsinks.
This is what this project is all about to come up with fairly easy to repeat alternative. After I tried a few variations, I came up with the fairly easy one - 4 x LED COBs mounted on commonly available fanned heatsink (this one from Amazon) by means of Arctic Thermal Epoxy. A bit of soldering to connect LED COBs in pairs and the board on top and all is done. Takes a day (for epoxy to dry) to get the fully operational solution.

As for the light sources - I am about to submit all of that (having tested all the LEDs to death now and finishing Xenon pulsed light source testing) but it will take me a few days to finish write ups. Hopefully will be on GitHub by the end of upcoming week.
Logged

Alexey.Danilchenko

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 257
    • Spectron


My copy of Hunt and Pointer's Measuring Color just arrived.  Quickly skimming through it, what you have been talking about makes a lot more sense.  None of the other color science books I described earlier covered any of this (what is covered starting in chapter nine of Measuring Color.) 

This book is essential if you want to venture into colour measurements. It was not leaving my desk pretty much for the last two years when Iliah and I started working on Spectron. The light sources section there is very interesting. Also the chapter about Precision and Accuracy of the measurements if of particular interest to me.
Logged

Iliah

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 770

OK, I'll have to wait until I have everything in front of me.

My copy of Hunt and Pointer's Measuring Color just arrived.  Quickly skimming through it, what you have been talking about makes a lot more sense.  None of the other color science books I described earlier covered any of this (what is covered starting in chapter nine of Measuring Color.)  The applied science portions of the older books were more about training chemists how to choose pigments so that plastic buttons matched sweater fabrics.   It was difficult to extrapolate that into spectral profiling of cameras.

Sometimes it is difficult to reduce unknown unknowns to known unknowns.

Measuring Color is the first step. Preferred reproduction of colour to follow. For a studio scene under halogen lights, in double blind test, participants consistently select a reproduction that resulted from a colour transform with mean dE 5.5, max dE 11 over the one resulting from colour transform with mean dE 3, max dE 5
Logged

WayneLarmon

  • Full Member
  • ***
  • Offline Offline
  • Posts: 162

Measuring Color is the first step. Preferred reproduction of colour to follow.

This?  The Reproduction of Colour 6th Edition

Or this?  Colour Reproduction in Electronic Imaging Systems: Photography, Television, Cinematography 1st Edition

Or something different?

Quote
For a studio scene under halogen lights, in double blind test, participants consistently select a reproduction that resulted from a colour transform with mean dE 5.5, max dE 11 over the one resulting from colour transform with mean dE 3, max dE 5

Meaning two different color transforms?  The first one provides more pleasing results even though it has a higher dE?
« Last Edit: June 24, 2018, 07:24:12 pm by WayneLarmon »
Logged

Iliah

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 770

Hunt's The Reproduction of Colour is IMHO very worth having.

> Meaning two different color transforms?  The first one provides more pleasing results even though it has a higher dE?

Exactly.
Logged

Tim Lookingbill

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2436

Quote
This? For a studio scene under halogen lights, in double blind test, participants consistently select a reproduction that resulted from a colour transform with mean dE 5.5, max dE 11 over the one resulting from colour transform with mean dE 3, max dE 5

Or something different?
Meaning two different color transforms?  The first one provides more pleasing results even though it has a higher dE?

Good grief! You might as well have a forger reproduce the paintings considering how many folks have lost millions thinking they had the real thing.

Those crappy Delta E numbers as the accepted color match pretty much makes this thread a waste of time.
Logged

Doug Gray

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2197

Or something different?
Meaning two different color transforms?  The first one provides more pleasing results even though it has a higher dE?


Good grief! You might as well have a forger reproduce the paintings considering how many folks have lost millions thinking they had the real thing.

Those crappy Delta E numbers as the accepted color match pretty much makes this thread a waste of time.

Reproducing an artwork to make a copy that looks the same side by side, is not the same thing as picking a reproduction on it's own that has the most appealing appearance. Nothing at all surprising about that. Quite a different issue than forgery.

There's a study out there using tunable, bumpy, illuminants which has the effect of generally increasing saturation over a Planckian locus or D source at the same CCT. It shows people finding the illuminated objects generally more appealing.
« Last Edit: June 25, 2018, 12:18:38 am by Doug Gray »
Logged

Tim Lookingbill

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2436

Reproducing an artwork to make a copy that looks the same side by side, is not the same thing as picking a reproduction on it's own that has the most appealing appearance. Nothing at all surprising about that. Quite a different issue than forgery.

There's a study out there using tunable, bumpy, illuminants which has the effect of generally increasing saturation over a Planckian locus or D source at the same CCT. It shows people finding the illuminated objects generally more appealing.

Doug, a "Pleasing Appearance" was not what I got out of this entire discussion going by the ton of technical minutiae generated in this thread on getting precise color match from paintings viewed and photographed under a given light spectra quality. This was what Wayne was going for, the ultimate light that would give a color match. So a halogen will suffice for getting pleasing color but not a color match according to Delta E numbers.

If pleasing color was the goal in this thread, could you point me to the posts that indicated this was the main objective? 
« Last Edit: June 25, 2018, 12:41:10 am by Tim Lookingbill »
Logged

Tim Lookingbill

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2436

Something else I just noticed about this thread on light spectra for photographic reproduction of paintings...

No one mentioned the camera profile as a factor affecting Delta E numbers.
Logged

Doug Gray

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2197

Doug, a "Pleasing Appearance" was not what I got out of this entire discussion going by the ton of technical minutiae generated in this thread on getting precise color match from paintings viewed and photographed under a given light spectra quality. This was what Wayne was going for, the ultimate light that would give a color match. So a halogen will suffice for getting pleasing color but not a color match according to Delta E numbers.

If pleasing color was the goal in this thread, could you point me to the posts that indicated this was the main objective?

It wasn't and no one here is saying it was. It's just an interesting side note.  I was responding to the comment reply #254.
Logged
Pages: 1 ... 11 12 [13] 14 15 ... 17   Go Up