05-25-2011, 06:23 AM
BC: You seem to have rewritten your old post totally, Russel. And a lot of misconceptions too, in that new post.
Sure Brightcolours, what do I know? After all, my only experience is writing Bayer filter array demosaicer software from scratch.
BC: You seem to not be aware that, besides chromatic information, each pixel also contains luminance information.
You figure I somehow missed that as I was writing the software? Yeah, each pixel also contains luminance information. The relative contributions of red, green and blue to luminance is about red 30%, green 59%, and blue 11%. Perhaps that's why I mentioned in my post that noise goes up a lot when you don't have much info from the relatively sweet green pixels. The contribution to luminance of, for example, blue information, isn't much.
BC: And it is only this luminance information which delivers detail.
Not sure what you're getting at, if there's alternating patches of hue that all have the same luminance, there'd be *no* detail?
BC:...But ALL pixels record luminance
Not a heck of a lot of perceived luminance information in the blue pixels, you seem to be glossing over "details" such as the fact that though, say, blue pixels contribute *something* to luminance, it's not a lot.
BC: ...Do take note that the moment the red, green or blue subject has gradations lighter than pure red/green/blue, the other colored sites will start to supply luminance information, even if the subject still looks red.
Have already covered this topic in my post, pointing out that as subjects *tend* towards missing more and more colors, performance *tends* downward. I.e. sure, Bayer sensors are better with some subjects. Heck they're great with gray subjects.
BC: Your assumption that colour temperature of light has any influence in what we are discussing is strange. 6500K light is NOT red, NOT blue and NOT green. So, all sensels will all deliver luminance information, same as with "white" light.
Your assumption that colour temperature of light has no influence on what we are discussing is strange to someone who's written demosaicing software. If the nonetheless bright ambient light is missing, especially, lots of blue, you have to amplify the noise-prone blue pixels lots more to get your final color-balanced image.
By the way, don't have to be a software author to observe this. Haven't you noticed the greater noise in incandescent-lit photos than greenish-fluorescent-lit or daylight-lit photos at same exposure value? I have.
BC: About high ISO noise...Where bayer sensors actually record 100% of the green part of the spectrum at the green sensels, with Foveon only about 50% of yellow gets recorded in the "green" layer...All in all, Foveon sensors have their very own noise problems, stemming from the loss of light through the different layers of silicon.
Nobody has said that any given Foveon sensor must have lower noise than any given Bayer sensor. What we can say is that while both Foveon and Bayer sensors probably change noise level with subject color, Foveon sensors don't ALSO change resolution with subject color. Which Bayer sensors do. And the Foveon edge is way more than 6% *in the* highly colored areas.
BC: As I have noted before, the difference between Bayer CFA sensors and Sigma/Foveon sensors in resolution recording is small, about 6-7% for normal scenes, if we only look at the CFA.
Foveon sensors are way better than 6% better in maintaining resolution in colored parts of scenes. I suppose you can add up how many parts of normal scenes are highly colored, and get the resolution edge down to 6% for the whole image, but you are glossing over the cases where the highly colored parts of the image might be of above average visual interest.
BC: However, this is quite hard to "measure", as Foveon/Sigma do not supply AA-filters with the sensors.
Since they have *less* need of one for most pictures, this is not cheating, it's a Foveon advantage.
BC: Without AA-filters, the results always will look more detailed
We agree.
BC: So.. if one really wants to visually compare the sensors, one...
Really what one should do is refrain from criticizing the SD1 sensor until one of us has had a chance to compare images of colored objects side-by-side with a 15 megapixel Bayer sensor of the same sensor size, and see which one if any looks better. If the Bayer camera has an AA filter it should be left in place as any normal user would do. My own impression of sample photos thus far is that the SD1 sensor output quality is superb, you seem to be talking an awful lot of theory and not talking much about sample photos.
BC: What I was putting forward is that the perceived difference in detail has much more to do with the missing AA-filter, than with the way the colours are recorded. And that is actually just a fact.
Saying it's a fact that a Bayer camera can get practically the same detail appearance/resolution from its blue pixels than from its possibly-missing-in-action green ones, doesn't make it so. Will point out for example the relative raggedness of the reddish sample photo shown a few posts back.
BC: [would like Foveon]...As long as it would have a suitable AA-filter, as I am not impressed by false detail, aliasing, moire and that "oversharpened" look.
If on the average, Foveon images look better to 51% or more of viewers than Bayer sensors of the same resolution and post-processing, they're just better. Whether you like the reasons for people's preferences or not. There is no law making camera manufacturers put on AA filters. If AA filters are needed for the Foveon, or are not needed for Bayer cameras, all will come out in image samples. IF AA-filterless Foveon cameras only "seem better" to most people for whatever reasons you may not like, then they're better.
BC it's just pretty outrageous for you to write theoretical SD1 criticisms before you or anyone on the Forum's had a chance to thoroughly check out side-by-side images at same ISO and sensor size. Save all your stuff until after you've looked at comparisons and seen with your own eyes that the Foveon's only "6% better".
Sure Brightcolours, what do I know? After all, my only experience is writing Bayer filter array demosaicer software from scratch.
BC: You seem to not be aware that, besides chromatic information, each pixel also contains luminance information.
You figure I somehow missed that as I was writing the software? Yeah, each pixel also contains luminance information. The relative contributions of red, green and blue to luminance is about red 30%, green 59%, and blue 11%. Perhaps that's why I mentioned in my post that noise goes up a lot when you don't have much info from the relatively sweet green pixels. The contribution to luminance of, for example, blue information, isn't much.
BC: And it is only this luminance information which delivers detail.
Not sure what you're getting at, if there's alternating patches of hue that all have the same luminance, there'd be *no* detail?
BC:...But ALL pixels record luminance
Not a heck of a lot of perceived luminance information in the blue pixels, you seem to be glossing over "details" such as the fact that though, say, blue pixels contribute *something* to luminance, it's not a lot.
BC: ...Do take note that the moment the red, green or blue subject has gradations lighter than pure red/green/blue, the other colored sites will start to supply luminance information, even if the subject still looks red.
Have already covered this topic in my post, pointing out that as subjects *tend* towards missing more and more colors, performance *tends* downward. I.e. sure, Bayer sensors are better with some subjects. Heck they're great with gray subjects.
BC: Your assumption that colour temperature of light has any influence in what we are discussing is strange. 6500K light is NOT red, NOT blue and NOT green. So, all sensels will all deliver luminance information, same as with "white" light.
Your assumption that colour temperature of light has no influence on what we are discussing is strange to someone who's written demosaicing software. If the nonetheless bright ambient light is missing, especially, lots of blue, you have to amplify the noise-prone blue pixels lots more to get your final color-balanced image.
By the way, don't have to be a software author to observe this. Haven't you noticed the greater noise in incandescent-lit photos than greenish-fluorescent-lit or daylight-lit photos at same exposure value? I have.
BC: About high ISO noise...Where bayer sensors actually record 100% of the green part of the spectrum at the green sensels, with Foveon only about 50% of yellow gets recorded in the "green" layer...All in all, Foveon sensors have their very own noise problems, stemming from the loss of light through the different layers of silicon.
Nobody has said that any given Foveon sensor must have lower noise than any given Bayer sensor. What we can say is that while both Foveon and Bayer sensors probably change noise level with subject color, Foveon sensors don't ALSO change resolution with subject color. Which Bayer sensors do. And the Foveon edge is way more than 6% *in the* highly colored areas.
BC: As I have noted before, the difference between Bayer CFA sensors and Sigma/Foveon sensors in resolution recording is small, about 6-7% for normal scenes, if we only look at the CFA.
Foveon sensors are way better than 6% better in maintaining resolution in colored parts of scenes. I suppose you can add up how many parts of normal scenes are highly colored, and get the resolution edge down to 6% for the whole image, but you are glossing over the cases where the highly colored parts of the image might be of above average visual interest.
BC: However, this is quite hard to "measure", as Foveon/Sigma do not supply AA-filters with the sensors.
Since they have *less* need of one for most pictures, this is not cheating, it's a Foveon advantage.
BC: Without AA-filters, the results always will look more detailed
We agree.
BC: So.. if one really wants to visually compare the sensors, one...
Really what one should do is refrain from criticizing the SD1 sensor until one of us has had a chance to compare images of colored objects side-by-side with a 15 megapixel Bayer sensor of the same sensor size, and see which one if any looks better. If the Bayer camera has an AA filter it should be left in place as any normal user would do. My own impression of sample photos thus far is that the SD1 sensor output quality is superb, you seem to be talking an awful lot of theory and not talking much about sample photos.
BC: What I was putting forward is that the perceived difference in detail has much more to do with the missing AA-filter, than with the way the colours are recorded. And that is actually just a fact.
Saying it's a fact that a Bayer camera can get practically the same detail appearance/resolution from its blue pixels than from its possibly-missing-in-action green ones, doesn't make it so. Will point out for example the relative raggedness of the reddish sample photo shown a few posts back.
BC: [would like Foveon]...As long as it would have a suitable AA-filter, as I am not impressed by false detail, aliasing, moire and that "oversharpened" look.
If on the average, Foveon images look better to 51% or more of viewers than Bayer sensors of the same resolution and post-processing, they're just better. Whether you like the reasons for people's preferences or not. There is no law making camera manufacturers put on AA filters. If AA filters are needed for the Foveon, or are not needed for Bayer cameras, all will come out in image samples. IF AA-filterless Foveon cameras only "seem better" to most people for whatever reasons you may not like, then they're better.
BC it's just pretty outrageous for you to write theoretical SD1 criticisms before you or anyone on the Forum's had a chance to thoroughly check out side-by-side images at same ISO and sensor size. Save all your stuff until after you've looked at comparisons and seen with your own eyes that the Foveon's only "6% better".