05-24-2011, 03:32 PM
(This post was last modified: 05-24-2011, 09:04 PM by Brightcolours.)
You seem to have rewritten your old post totally, Russel.
And a lot of misconceptions too, in that new post.
You seem to not be aware that, besides chromatic information, each pixel also contains luminance information. And it is only this luminance information which delivers detail.
So, of course you are right in saying that only 25% of pixels actually record red light, And that only 25% of the pixels record blue light. And that 50% of the pixels record green light.
But ALL pixels record luminance, and after good de-mosaicking and interpolating, you get much more detail than you are suggesting.
The difference between Bayer CFA and Foveon/Sigma is very low, a bit more than 6% of resolution.
Of course, with only pure red (so no gradations of lighter red) with black patterns, or pure blue with black patterns, resolution can be less, But that is not really a significant aspect, just a theoretical one.
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.
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.
About high ISO noise, Foveon has its very own noise problem: Its sensor does not record all of the light. Where with bayer CFA, at all pixels all of the light of either the red, the green or the blue part of the spectrum get recorded,
Foveon sensors actually do not record red, green and blue. It is more like blue, yellow and red.
Of the blue, all blue gets recorded. However.... also part of the yellow and red gets recorded.
This means two things:
- The sensel is filled up not just with blue, but also probably with some yellow and some red, depending on the actual subject. It reaches filled status sooner than if it were only to record blue light.
- It also means that one has to do interpolation to determine how much of the recorded energy actually stems from the blue light spectrum.
Below the "blue" layer lays the yellow layer. This layer not only records yellow light, but also some of the red spectrum.
This means 4 things:
- The yellow light reaching the yellow layer is about 1/2 of the yellow light reaching the sensor, the other half has been captured in the blue layer.
- One has to use interpolation to determine how much of the recorded energy stems from actual yellow, and what is from the red spectrum.
- One has to interpolate to figure out what actually has been "green", as the recorded spectrum of light is yellow.
- What has been recorded in the yellow layer is still being polluted with red, meaning the sensel can fill up sooner than if it only would be recording yellow.
Below the yellow layer lays the red layer.
- The red layer only receives about 1/3rd of the red light that reached the sensor. The rest of the red is polluting the blue and yellow layer.
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. This is then also still polluted with red.
To get green values, one does not only have to interpolate the red away. but also interpolate against the blue channel, to determine green.
With red, only a small amount of the red light gets captured. Because this means a very noisy red channel, the red channel actually gets blurred as noise reduction measurement.
All in all, Foveon sensors have their very own noise problems, stemming from the loss of light through the different layers of silicon. And Foveon sensors have their own areas of "colour blindness".
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.
However, this is quite hard to "measure", as Foveon/Sigma do not supply AA-filters with the sensors.
Without AA-filters, the results always will look more detailed (even though, most of the detail is false detail from pixels just having edges.. and so, making edges. But AA-filters have little to do with CFA's.... they are about trying to not record the false detail.
So.. if one really wants to visually compare the sensors, one either has to test a SIgma/Foveon next to a Bayer-CFA sensor without AA-filter, or one needs to put an AA-filter suiting the sensor's pixel pitch in front of the Foveon sensor, so its false detail does not pollute the results.
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.
That the foveon sensor can still have an advantage in unusual situations (like a black pattern on a pure primary colour) is obvious, and that it has its own disadvantages in certain situations is also known.
I have nothing against a foveon sensor, in fact, I would not mind at all if my camera had one (that would behave in higher ISO shooting too). As long as it would have a suitable AA-filter, as I am not impressed by false detail, aliasing, moire and that "oversharpened" look.
And a lot of misconceptions too, in that new post.
You seem to not be aware that, besides chromatic information, each pixel also contains luminance information. And it is only this luminance information which delivers detail.
So, of course you are right in saying that only 25% of pixels actually record red light, And that only 25% of the pixels record blue light. And that 50% of the pixels record green light.
But ALL pixels record luminance, and after good de-mosaicking and interpolating, you get much more detail than you are suggesting.
The difference between Bayer CFA and Foveon/Sigma is very low, a bit more than 6% of resolution.
Of course, with only pure red (so no gradations of lighter red) with black patterns, or pure blue with black patterns, resolution can be less, But that is not really a significant aspect, just a theoretical one.
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.
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.
About high ISO noise, Foveon has its very own noise problem: Its sensor does not record all of the light. Where with bayer CFA, at all pixels all of the light of either the red, the green or the blue part of the spectrum get recorded,
Foveon sensors actually do not record red, green and blue. It is more like blue, yellow and red.
Of the blue, all blue gets recorded. However.... also part of the yellow and red gets recorded.
This means two things:
- The sensel is filled up not just with blue, but also probably with some yellow and some red, depending on the actual subject. It reaches filled status sooner than if it were only to record blue light.
- It also means that one has to do interpolation to determine how much of the recorded energy actually stems from the blue light spectrum.
Below the "blue" layer lays the yellow layer. This layer not only records yellow light, but also some of the red spectrum.
This means 4 things:
- The yellow light reaching the yellow layer is about 1/2 of the yellow light reaching the sensor, the other half has been captured in the blue layer.
- One has to use interpolation to determine how much of the recorded energy stems from actual yellow, and what is from the red spectrum.
- One has to interpolate to figure out what actually has been "green", as the recorded spectrum of light is yellow.
- What has been recorded in the yellow layer is still being polluted with red, meaning the sensel can fill up sooner than if it only would be recording yellow.
Below the yellow layer lays the red layer.
- The red layer only receives about 1/3rd of the red light that reached the sensor. The rest of the red is polluting the blue and yellow layer.
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. This is then also still polluted with red.
To get green values, one does not only have to interpolate the red away. but also interpolate against the blue channel, to determine green.
With red, only a small amount of the red light gets captured. Because this means a very noisy red channel, the red channel actually gets blurred as noise reduction measurement.
All in all, Foveon sensors have their very own noise problems, stemming from the loss of light through the different layers of silicon. And Foveon sensors have their own areas of "colour blindness".
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.
However, this is quite hard to "measure", as Foveon/Sigma do not supply AA-filters with the sensors.
Without AA-filters, the results always will look more detailed (even though, most of the detail is false detail from pixels just having edges.. and so, making edges. But AA-filters have little to do with CFA's.... they are about trying to not record the false detail.
So.. if one really wants to visually compare the sensors, one either has to test a SIgma/Foveon next to a Bayer-CFA sensor without AA-filter, or one needs to put an AA-filter suiting the sensor's pixel pitch in front of the Foveon sensor, so its false detail does not pollute the results.
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.
That the foveon sensor can still have an advantage in unusual situations (like a black pattern on a pure primary colour) is obvious, and that it has its own disadvantages in certain situations is also known.
I have nothing against a foveon sensor, in fact, I would not mind at all if my camera had one (that would behave in higher ISO shooting too). As long as it would have a suitable AA-filter, as I am not impressed by false detail, aliasing, moire and that "oversharpened" look.