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Author Topic: Sensor & Sensibility II  (Read 26464 times)

jani

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« Reply #20 on: August 26, 2006, 10:49:58 am »

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But once again, Bill, you don't alsways have the same need for the higher ISOs with a camera like the D2X. You can usually get the same results with a 1.5 stops bigger aperture and correspondingly lower ISO.
I think you must have typed something else than what you meant, since this seems to require that Nikon provide lenses with 1.5 stops more of headroom than Canon.
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bjanes

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« Reply #21 on: August 26, 2006, 12:38:08 pm »

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What you are fixating on is specifics of a particular argumentation and technical babble.

If anyone can back up the techno babble with some serious evidence then the arguments might be taken more seriously.
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Babble definition (dictionary.com):

6.   inarticulate or imperfect speech.
7.   foolish, meaningless, or incoherent speech; prattle.
8.   a murmuring sound or a confusion of sounds.

If you regard scientific analysis as babble, then I truly feel sorry for you. These sceintific  principles have been verified many times over. A camera sensor can defy the laws of phycics no better than a perpetual motion machine can defy the laws of mechanics. While you are tyring to perfect such a machine, I will be engaged in more productive work.
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32BT

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« Reply #22 on: August 26, 2006, 12:46:09 pm »

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I think it is very likely that a 400D would have narrowed this gap to irrelevancy at any enlargement, under these conditions of same DoF and shutter speed.

On the contrary.

This is exactly what makes it interesting. How do people judge image quality, and, more importantly, how does one judge the overal picture subjectively, especially in the wake of processing artifacts. The processing artifacts may not be clearly defined at certain sizes, but they may certainly impact the overal subjective picture "experience" if you will. These images are a good example:

The 5D shows clear signs of clipping or over-exposed areas, possibly because of reduced dynamic range due to higher iso.

The 20D shows clear blooming and aliasing artifacts. The latter especially will increase in number and become more pronounced in the 400D images if more processing is necessary to gain otherwise similar results. It is also these artifacts that IMO produce a less pleasing, subjective overall picture experience. From experience I know that, eventually, even the lay-man viewer can see this and experiences a kind of grainyness in the overal image that is unpleasant or even tiring.
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bjanes

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« Reply #23 on: August 26, 2006, 12:54:34 pm »

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What you are fixating on is specifics of a particular argumentation and technical babble.

If anyone can back up the techno babble with some serious evidence then the arguments might be taken more seriously.
[a href=\"index.php?act=findpost&pid=74537\"][{POST_SNAPBACK}][/a]

Babble definition (dictionary.com):

6.   inarticulate or imperfect speech.
7.   foolish, meaningless, or incoherent speech; prattle.
8.   a murmuring sound or a confusion of sounds.

If you regard scientific analysis as babble, then I truly feel sorry for you. These sceintific  principles have been verified many times over. A camera sensor can defy the laws of phycics no better than a perpetual motion machine can defy the laws of mechanics. While you are tyring to perfect such a machine, I will be engaged in more productive work.
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DiaAzul

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« Reply #24 on: August 26, 2006, 05:25:09 pm »

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These sceintific  principles have been verified many times over.
[a href=\"index.php?act=findpost&pid=74551\"][{POST_SNAPBACK}][/a]

You mean scientific principles such as the earth is flat...

I don't mind a good qualified, well justified and rational discussion. But a lot of what is being regurgitated here is just a bunch of sheep recounting what they have read elsewhere on the internet - it is about as far away from rigorous scientific analyis as you can get.

The key point I continue to try and make is that technology will advance, image quality will improve and customer requirements will continue to move forward to capitalise on new equipment and what it can do for them. As far as I understand that is what Oscar was trying to postulate at the start and to try and avoid a rehashed technical discussion that is marginally relevant to most people who are interested in actually taking pictures rather than slaving over technical nuances that may, or may not, actually matter at the end of the day.

People who obsess about the size of their pixels are just a bunch of boring internet nerds with no real relevance to actual photography. Do we really have to judge a person by the size of their pixel? Is it important that you have a high dynamic range? Or is that a 1DsIII in you pocket or are you just pleased to see her?

As Cuba Gooding Jr once said to Tom Cruise - Show me the image. If you can talk the talk, the please (for heavens sake) show us that all this technology actually translates into better pictures.
« Last Edit: August 26, 2006, 05:33:01 pm by DiaAzul »
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Ray

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« Reply #25 on: August 26, 2006, 10:37:00 pm »

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The 5D shows clear signs of clipping or over-exposed areas, possibly because of reduced dynamic range due to higher iso.

More likely because of a lack of a completely rigorous methodology. The illumination for this scene was daylight through the lounge window, which during the course of stuffing around, changing cameras and lenses, trying to get focussing accurate etc etc, would have changed slightly during the period of the testing process. I took a series of shots at 1/3rd stop intervals at various ISO settings on both cameras and then tried to match same exposure shots that were fully exposed to the right. I converted in ACR with shadows and contrast settings at zero and did my best to get the histograms looking the same, with appropriate amounts of negative EC. But the amounts are not identical in these comparisons. There's was a limit to the amount of time I was prepared to spend to get every aspect completely accurate, especially when the tests were flawed from the beginning by using a 75mm focal length with the 5D instead of 80mm. (Both cameras were used on the same tripod from the same position).

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The 20D shows clear blooming and aliasing artifacts.

On a 20x30" print? I think I know what you are referring to. Below is a pair of 400% crops showing an enlarged specral highlight at the bottom fringed by a more pronounced, jagged edge in the 20D crop. Is this the sort of thing you mean?

This 400% crop is 5 1/2 inches wide on my screen and, by my calculation, represents a print size of 10ftx15ft. The image is in vertical orientation.

If I were to make a print this size, for any unimaginable reason, I'd be uprezzing with Genuine Fractals and no doubt introducing a lot more artifacts. I think we're into serious pixel peeping here, Oscar   .

[attachment=923:attachment]
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Ray

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« Reply #26 on: August 26, 2006, 11:00:07 pm »

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I think you must have typed something else than what you meant, since this seems to require that Nikon provide lenses with 1.5 stops more of headroom than Canon.
[a href=\"index.php?act=findpost&pid=74547\"][{POST_SNAPBACK}][/a]

Jani,
I should have emphasised the word always. If both the Nikon D2X user and 5D user have an f2 lens of equivalent focal lengths so they can get the same shot from the same distance, the 5D user gets the opportunity to take a shot which is less noisy but which also has less DoF. If the shallowest DoF possible is your goal, the 5D user has a clear advantage of both a less noisy image and one with shallower DoF. As far as I know, there is no 10mm or 11mm f2.8 lens for the cropped format, equivalent to the Canon 16-35/2.8, which is another disadvantage for D2X users. Is that right?
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John Sheehy

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« Reply #27 on: August 26, 2006, 11:14:00 pm »

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The 20D shows clear blooming and aliasing artifacts.[a href=\"index.php?act=findpost&pid=74555\"][{POST_SNAPBACK}][/a]

Can you link to a 20D image that has blooming?

I've never heard of blooming in Canon CMOS sensors.

The purple halos you get around extremely bright edges are infrared light out of focus, IMO.
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John Sheehy

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« Reply #28 on: August 26, 2006, 11:25:48 pm »

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Have you been on a special course to teach how to write bollocks dressed as techno-babble? As per your earlier comment on dynamic range which bjanes saved me the effort of commenting on, this is a complete load of drivel put in such a way as to sound intelligent.

The only thing being stained here is credibility.
[a href=\"index.php?act=findpost&pid=74531\"][{POST_SNAPBACK}][/a]

I've always been intrigued by the fact that moderated forums always have more rude people than usenet, where satan himself can post and say anything he wants.

... and what I said made perfect sense.  A sensor with a coarser pixel pitch doesn't require the MTF performance of one with a finer pixel pitch.  Is that so difficult to comprehend?
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Ray

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« Reply #29 on: August 27, 2006, 12:01:03 am »

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If you're running Windows, there's been a calculator included with the system since version 1.0 in 1985.
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Sometimes the obvious escapes me   . So, having done a few precise sqrt calculations, instead of moving backwards 1.6x the distance to the target with the 20D (to get same FoV as the 5D with same lens), I should move back just 1.265x the distance, to get an equal number of pixels in equal FOV crops. Is that right?
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32BT

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« Reply #30 on: August 27, 2006, 02:09:30 am »

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More likely because of a lack of a completely rigorous methodology. The illumination for this scene was daylight through the lounge window,

way to go Ray. F**k up the primary, most fundamental step in the Photographic process. Read the sarcasm. This test wasn't flawed because of the lens issue...
Bad dog Ray, bad bad dog...


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This 400% crop is 5 1/2 inches wide on my screen and, by my calculation, represents a print size of 10ftx15ft. The image is in vertical orientation.

If I were to make a print this size, for any unimaginable reason, I'd be uprezzing with Genuine Fractals and no doubt introducing a lot more artifacts. I think we're into serious pixel peeping here, Oscar   .

Nope, it doesn't work that way, and you seem to miss my point.

Let me try to give you a visual analogy. We all know the common wisdom from the printing industry that a good print requires about 2x the raster lpi. Which translates to about 300dpi resolution for a common print situation and which is now also used for inkjet printing.

But have you ever wondered what the resolution for text and line elements is supposed to be according to that same industry?

It ranges anywhere from 1200dpi to 2400dpi. Why is that?
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32BT

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« Reply #31 on: August 27, 2006, 03:29:58 am »

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Can you link to a 20D image that has blooming?

I've never heard of blooming in Canon CMOS sensors.

The purple halos you get around extremely bright edges are infrared light out of focus, IMO.

That may be true. I was referring to the metal piece. But especially the left side is intriguing. The 20D image shows relatively large blobs of discolorisation. The 5D image, which appearantly has more contrasty light shining at it, doesn't seem to suffer the same issues. Could be a better IR filter, or even the lens performance of course.



Point is that even though we (as imaging professionals) need pixel-peeping to explain what we see, the net effect on a simple 8x5 image appearantly is a sense of graininess that is tiring to the eyes. Jagged edges are a prime example. A beautifully anti-aliased edge vs a jagged edge (you know it when you see it) makes a world of difference in final image appearance. To explain the phenomenon requires pixel-peeping of the highest degree. But to appreciate anti-aliasing requires a normal print or viewing situation.
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DiaAzul

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« Reply #32 on: August 27, 2006, 07:35:19 am »

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That may be true. I was referring to the metal piece. But especially the left side is intriguing. The 20D image shows relatively large blobs of discolorisation. The 5D image, which appearantly has more contrasty light shining at it, doesn't seem to suffer the same issues. Could be a better IR filter, or even the lens performance of course.
[a href=\"index.php?act=findpost&pid=74619\"][{POST_SNAPBACK}][/a]

This has been a long standing issue around specular highlights and contrasty edges and (IMHO) is generated by a combination of clipping of the RAW data due to insufficient dynamic range in the sensor and the effect of interpolation of beyer data to generate the final image.

The clipping of the RAW data is before application of the tonal curve, so the in camera histogram is not particularly useful for assessing the impact of this problem at the time that the shot is taken and, as these are specular highlights, it is unlikely that you would see them in the histogram either - a classic case where exposing to far to the right has its draw backs.

I suspect that because the 5D has a greater dynamic range then the green channel is clipping much later than for the 20D and, therefore, it is possible during the interpolation process to recover the colour information. However, for the 20D (and areas where a colour shift is perceptible in the 5D image) the green channel looks as if it has blown out first whilst either the red and/or blue channels continue to increase in value. As the RAW converter doesn't know by how much the green channel has blown out then it has to guess at the colour for those pixels where this effect has taken place. Where there is a continuous tone then it is not unreasonable to extend the same colour information across the surface, however, at edges transitioning from one tone to another then it becomes very difficult to best guess the required colour information and the RAW convertor tends to get things wrong.

Two further points:
1/ You appear to be applying a high level of capture sharpening to your images. This will emphasise any 'jaggies' along the edges. Try easing back a bit on the sharpening if you are getting overly harsh and noisy pictures.

2/It is very unlikely that IR will affect the sensor, Canon (much to the disappointment of IR photographers) has a very tight IR and UV filter on the front of the sensor which blocks most IR radiation from ever getting near the sensor itself. However, the UV filter doesn't appear to be quite so tight which affects flower photographers who tend to get blown out details in the petals if an additional UV filter is applied or exposure compensation is used.
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Ray

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« Reply #33 on: August 27, 2006, 07:52:22 am »

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This test wasn't flawed because of the lens issue...

Good! A 75mm FL instead of 80mm gives a slight advantage to the 20D, but I think it's quite fair to give an advantage to the underdog, don't you?  

As I see you are a painstakingly thorough sort of guy, I'll repost the images without any sharpening, WB adjustment or tweaking of the histogram. It has now occurred to me that the exposure differences in the earlier examples could have been partly due to the discrepancy in FL equivalence. The 5D shot takes in a slightly greater expanse of lighter shades. The true ISO values might also vary to different degrees between the 2 cameras, although I get the impression they are roughly the same.

I've converted the following images in ACR, with zero shadows and contrast, no sharpening, no luminance smoothing, no post processing, no nothing except EC adjustment, cropping. conversion to srgb and maximum quality jpeg compression.

I've reselected the images, but to get the histograms looking the same, I'm comparing a 5D image with 1/5th sec exposure and minus 0.9 EC, with a 20D image with 1/4 sec exposure and minus 1 EC. (Is this called fudging the results?) I've included screen shots of the histograms.

[attachment=927:attachment]  [attachment=928:attachment]  [attachment=929:attachment]  [attachment=930:attachment]

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Nope, it doesn't work that way, and you seem to miss my point.

Let me try to give you a visual analogy. We all know the common wisdom from the printing industry that a good print requires about 2x the raster lpi. Which translates to about 300dpi resolution for a common print situation and which is now also used for inkjet printing.

Oscar, I'm not suggesting I would print the 10ftx15ft image at the screen resolution of 96 dpi. Of course I wouldn't. I'd interpolate the image to 240 ppi with GF, as I mentioned. The file size would then be huge. The point I'm making, which you seem to have missed, is that the 5 1/2" wide 400% crop which I'm scrutinising on my monitor from the distance one might view an 8x10" print, is part of a 10ftx15ft image. In other words, if I wanted to see the whole image at this degree of detail and at this resolution of 96 dpi, my monitor would need to be 15ft high and 10ft wide.
« Last Edit: August 27, 2006, 07:55:56 am by Ray »
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32BT

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« Reply #34 on: August 27, 2006, 09:01:40 am »

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Good! A 75mm FL instead of 80mm gives a slight advantage to the 20D, but I think it's quite fair to give an advantage to the underdog, don't you? 

I'm all for the underdog. Speaking of which: could you repost DPP conversions of the same files? (or post the RAW).

It seems the 20D is outresolving the lens by a fair amount, any way we can change that?

What could be the source of the rather significant chromatic aberration in the 20D file?

Would it be interesting to change the 20D iso to its optimal value, and set the 5D to what you consider the equivalent?

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Oscar, I'm not suggesting I would print the 10ftx15ft image at the screen resolution of 96 dpi. Of course I wouldn't. I'd interpolate the image to 240 ppi with GF, as I mentioned.
I know, but that was not the question. The question is: why does the industry want 1200dpi to 2400dpi for text and line-art?
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32BT

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« Reply #35 on: August 27, 2006, 09:20:11 am »

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This has been a long standing issue around specular highlights and contrasty edges and (IMHO) is generated by a combination of clipping of the RAW data due to insufficient dynamic range in the sensor and the effect of interpolation of beyer data to generate the final image.

But this would thus result in a clear and obvious sample of better performance of larger-pixel-bin sensors vs smaller-pixel-bin. That is, at the current state of affairs. I completely agree with you that the performance of smaller-pixel-bins can and will increase.

As a matter of fact, eventually the larger-pixel-bin advantage may for example be countered by speed advantages of reading smaller-pixel-bins. I'm purely speculating here, but I recall research about taking multiple exposures in a single exposure. Eventually the read-out speed may make this viable for smaller-pixel-bins, but larger pixel-bins simply don't "fill up" quick enough, their "native" iso being to high?

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2/It is very unlikely that IR will affect the sensor, Canon (much to the disappointment of IR photographers) has a very tight IR and UV filter on the front of the sensor which blocks most IR radiation from ever getting near the sensor itself. However, the UV filter doesn't appear to be quite so tight which affects flower photographers who tend to get blown out details in the petals if an additional UV filter is applied or exposure compensation is used.

But Canon made a relatively big deal out of the newer filters applied in the 5D. So there may well be a difference between a 20D and 5D. It also begs the question: Are these newer filters applied in the new 400D?
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John Sheehy

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« Reply #36 on: August 27, 2006, 09:30:23 am »

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If you're running Windows, there's been a calculator included with the system since version 1.0 in 1985.
[a href=\"index.php?act=findpost&pid=74545\"][{POST_SNAPBACK}][/a]

It has no square root function, per se.  You have to use the x^y with 0.5 as the exponent.
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John Sheehy

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« Reply #37 on: August 27, 2006, 09:45:43 am »

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That may be true. I was referring to the metal piece. But especially the left side is intriguing. The 20D image shows relatively large blobs of discolorisation. The 5D image, which appearantly has more contrasty light shining at it, doesn't seem to suffer the same issues. Could be a better IR filter, or even the lens performance of course.


It can also be the 5D's coarser pixel pitch.  Imagine that the pixels were even bigger, and the fringes occured only in a very small percentage of any given pixel.  The effect will be almost invisible.  This is the fact that Diazul argued against and insulted me for; the 5D pixels gather more high contrast material, and less blurred edge effects, because optical edges are a smaller percentage of any given pixel's capture.

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Point is that even though we (as imaging professionals) need pixel-peeping to explain what we see, the net effect on a simple 8x5 image appearantly is a sense of graininess that is tiring to the eyes. Jagged edges are a prime example. A beautifully anti-aliased edge vs a jagged edge (you know it when you see it) makes a world of difference in final image appearance. To explain the phenomenon requires pixel-peeping of the highest degree. But to appreciate anti-aliasing requires a normal print or viewing situation.
[a href=\"index.php?act=findpost&pid=74619\"][{POST_SNAPBACK}][/a]

For that I thank Canon for not falling into the trap of creating false detail sharpness with very weak or absent AA filters, like some other MFRs have done.  I also appreciate that they give you fairly raw RAW files, complete with "negative" values (less than black).  Even though Canon itself doesn't seem to use this data in its converters for anything, I find it invaluable for subtracting line noise in extremely underexposed images.  I hope these things remain for future cameras.
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John Sheehy

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« Reply #38 on: August 27, 2006, 10:22:42 am »

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This has been a long standing issue around specular highlights and contrasty edges and (IMHO) is generated by a combination of clipping of the RAW data due to insufficient dynamic range in the sensor and the effect of interpolation of beyer data to generate the final image.

That certainly acounts for flat clipped areas, without the necessary intelligence to recognize clipping in the converter.

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I suspect that because the 5D has a greater dynamic range then the green channel is clipping much later than for the 20D

That's not true at all ISOs. 100 has greater DR by about a half-stop (part of the reason is that 0.25 stops is missing in the 20D), and the highest ISOs have greater on the 5D, but at 200 and 400, they are roughly the same.

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and, therefore, it is possible during the interpolation process to recover the colour information. However, for the 20D (and areas where a colour shift is perceptible in the 5D image) the green channel looks as if it has blown out first whilst either the red and/or blue channels continue to increase in value. As the RAW converter doesn't know by how much the green channel has blown out then it has to guess at the colour for those pixels where this effect has taken place. Where there is a continuous tone then it is not unreasonable to extend the same colour information across the surface, however, at edges transitioning from one tone to another then it becomes very difficult to best guess the required colour information and the RAW convertor tends to get things wrong.

I certainly hope that interpreting this as color never becomes a converter default.  

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2/It is very unlikely that IR will affect the sensor, Canon (much to the disappointment of IR photographers) has a very tight IR and UV filter on the front of the sensor which blocks most IR radiation from ever getting near the sensor itself.

It is only a relative effect that the IR-cut filter has.  It cuts a percentage; it is not 100% effective.  When you get specular highlights that concentrate light on the sensor that is several stops stronger than 100% matte reflectance, and you are metering for 12-18%, the IR content is also much stronger than usual in that highlight.  If the lens focuses IR much differently than it does visible light, then you get bokeh where the IR should be focused, creating a halo.  This *has* to be happening at some level, even if you discard the idea as the main reason.

I have looked at other people's test results, and the purple fringing effect does not vary with exposure, and it varies quite a bit with lenses.  That is one reason that I conclude that it is OOF IR.  If you shoot IR with a 93 filter, the results are purple.

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However, the UV filter doesn't appear to be quite so tight which affects flower photographers who tend to get blown out details in the petals if an additional UV filter is applied or exposure compensation is used.
[a href=\"index.php?act=findpost&pid=74629\"][{POST_SNAPBACK}][/a]

What kind of petals are you talking about?  The typical blown-out red petal is not blown out or even close to blowing out in the RAW data.  It is an artifact of converters trying to get a saturation in the color space that approaches the petal in human perception.  The blue channel is very dark in red petals, the red is strongest but green is fairly strong because of the overall higher sensitivity in the green channel.
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DiaAzul

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« Reply #39 on: August 27, 2006, 11:47:22 am »

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It cuts a percentage; it is not 100% effective.  When you get specular highlights that concentrate light on the sensor that is several stops stronger than 100% matte reflectance, and you are metering for 12-18%, the IR content is also much stronger than usual in that highlight.  If the lens focuses IR much differently than it does visible light, then you get bokeh where the IR should be focused, creating a halo.  This *has* to be happening at some level, even if you discard the idea as the main reason.

[a href=\"index.php?act=findpost&pid=74646\"][{POST_SNAPBACK}][/a]

That's a fair comment. Though the cutoff on the filters is quite steep and out of focus areas are going to be spread out and difuse disipating the incident energy over multiple pixels. The purple halos are very intense and it would take a large amount of incident light to achieve the effect which is visible in the images.

For specular highlights I would tend to agree with what you have described, however, this is only so where the source of light is particularly strong. Where the sensor is only just clipped then other effects which are the result of interplay between clipping, bayer sensors and interpolation in the RAW convertor are probably more likely.
« Last Edit: August 27, 2006, 12:09:53 pm by DiaAzul »
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