Camera's histogram reliable to the RAW data

[John Sheehy]

You certainly would not get the same, because the colors of a single tri-color pixel would have to undergo "only" a color space transformation, while the de-mosaicing has to work with several neighbouring pixels, where the distance between them is relevant too (and the result undergoes the color space conversion).

That's still not relevant.  That's only a spatial issue (resolution), not a color issue.

Nevertheless, there is no saturated color on raw level.

Sure there is.  Have you ever shot red or blue LEDs?  You can have one color channel almost clipping, while another is down near the noise floor; the green response is weak but significant.  I have seen shadows cast from an LED in the "right" color on bulbs, viewed in the "wrong" RAW channel.  Looks like they aren't even on at all, and you have to take a shot with just that one bulb on to see it in the "wrong" channel, buried down in the noise.  But no one claimed 100% saturation.

You can not find any wavelength, which would be totally filtered by two channels. Theoretically, one wavelength per filter would be acceptable, but this irrelevant, and anyway there are no such filters.

Who said two channels?  Only one has to mostly miss it for it to be considered saturated.  How do you record a yellow or violet or cyan laser?  How do you display it?  You sometimes must depend on two colors for recording and displaying saturation (not ideal, of course).  Saturation is emulated by dropping the weaker channel more than it is really recorded in RAW, while applying a push into the ceiling" curve to the other two colors.

I have a deep blue 77mm filter that drops everything on the red side of green down into the noise.  I have a "pad" of gel samples, some of which, when looking at a spectrum through a diffraction grating, look black in certain ranges.

So, you can have many different color compositions from different saturated colors (single wavelengths),  which have to be transformed in different RGBs; only one of them may be transformed in a fully saturated color.
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Could you rephrase that, and make your point clearer.

[bernie west]

Panopeeper Posted Today, 05:08 AM
I stated, that DoF depends on the lens, but not on the cropping; this is a fact. It is not useful to mix up concepts.

True, but that is not all it depends on.  Any comparison discussion about DOF between formats must be concerned with equivalent FOV, or else it's pointless.  The question should be - can I essentially capture the same image on two different formats.  In the case of extremes of DOF range, the answer is often no.

[Guillermo Luijk]

I stated, that DoF depends on the lens, but not on the cropping; this is a fact. It is not useful to mix up concepts.

Sensor format and lens have to be mixed to find out which sensor can provide more bokeh for a given lens.
In more understandable terms: given a lens with a maximum aperture (e.g. a 85mm f1. and shooting over the same subject, a 5D will achieve a narrower DoF (i.e. more bokeh) than a 40D, because the 5D will allow us to get closer to the subject to obtain the same FoV over the subject, then reducing DoF.
This is what I meant.

The same story applies in wide angle lenses: wide angles lenses do not distort perspective since perspective does not depend on the lens but on the distance to the subject. But wide angle lenses allow us to get closer to the subject, and it is then when perspective changes.

[Panopeeper]

Sensor format and lens have to be mixed to find out which sensor can provide more bokeh for a given lens.

The ability to abstract details is essential for the understanding of issues.

[Panopeeper]

That's still not relevant.  That's only a spatial issue (resolution), not a color issue

The spatial distribution is not "only" when evaluating the color, but irrelevant in the current context.

Have you ever shot red or blue LEDs?  You can have one color channel almost clipping, while another is down near the noise floor; the green response is weak but significant

I shot red laser light. The blue was very low, but the green was considerable, about 25% of the red. Of course, this depends on the wavelength.

Who said two channels?  Only one has to mostly miss it for it to be considered saturated

1. In the RGB model the yellow is a composite color. There is no important difference between yellow and any other color.

2. *All colors* appear in *at least two kinds of pixels* to a meaningful degree. This fact makes it possible to differentiate between colors of the same "range", for example between red colors; otherwise the Bayer sensor would not work with multicolor.

[John Sheehy]

The spatial distribution is not "only" when evaluating the color, but irrelevant in the current context.
I shot red laser light. The blue was very low, but the green was considerable, about 25% of the red. Of course, this depends on the wavelength.
1. In the RGB model the yellow is a composite color. There is no important difference between yellow and any other color.

2. *All colors* appear in *at least two kinds of pixels* to a meaningful degree. This fact makes it possible to differentiate between colors of the same "range", for example between red colors; otherwise the Bayer sensor would not work with multicolor.
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Why are you telling me all this?

Most of what you seem to be saying here is what I have already said, yet you seem to be disagreeing with me.

I have serious difficulty following a conversation with you.

[Panopeeper]

Why are you telling me all this?

I have serious difficulty following a conversation with you.

Let's recapitulate it. I posted earlier:

I think you stretched the concept over the limit. We can practicall turn off white balancing, we can turn off contrast and saturation, but we can't turn off the de-mosaicing

and your opinion was, that this played no role in the phenomenon Jonathan observed:

I don't see how demosaicing would be relevant. You would get the same relatively saturated capture if R, G, and B were co-located

All this time I tried to explain you, that the de-mosaicing does change pure colors in composite ones, and thus it causes the contradiction between the raw and RGB histograms.

Another issue is, that even with tri-colored pixels a conversion would have to occur with like effect (i.e. converting pure colors in composite ones), but this does not really matter, for the sensor in the experiment is a Bayer one..

Anyway, I stand by my assertion, that the de-mosaicing is the cause of the phenomenon Jonathan observed with the LED lights.

[Jonathan Wienke]

All this time I tried to explain you, that the de-mosaicing does change pure colors in composite ones, and thus it causes the contradiction between the raw and RGB histograms.

De-mosaicing has nothing to do with it. A Foveon sensor would behave similarly, with a single-wavelength light source such as an LED or laser stimulating a response in more than one channel. Converting pure colors to composite colors is a product of the frequency response of the color filter array, pure and simple. You can observe this in the RAW data before demosaicing occurs:



This histogram is from one of my red LED test photos.

[John Sheehy]

Anyway, I stand by my assertion, that the de-mosaicing is the cause of the phenomenon Jonathan observed with the LED lights.
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Then you are out on a limb, IMO.  The only difference of a bayer CFA here is one of spatial resolution.  There is no color-related magic in co-location.  The only reason for demosaicing over straight, independent interpolation of each isolated color plane, is that you get to abstract per-pixel luminance.  If you wanted a 3MP conversion of a 12MP sensor, you wouldn't even need to demosaic; it would serve no purpose.  You would just interpolate each color plane (maintaining its offset), and then downsample or bin to 3 MP.

[Jonathan Wienke]

FWIW, I've posted my 1Ds and 1D-Mark II UniWB RAWS online at:

http://www.visual-vacations.com/images/2008/

[Panopeeper]

De-mosaicing has nothing to do with it. A Foveon sensor would behave similarly, with a single-wavelength light source such as an LED or laser stimulating a response in more than one channel

I stated just above, that this would occur with tri-colored pixels as well. However, creating composite colors from Bayer pixels is part of the de-mosaicing process.

[Panopeeper]

I normally do HDR (not the tone mapping, just getting the HDR data) from 2 shots: 0EV, +4EV. To obtain them I bracket -2,0,2, so that the -2 matches my desired 0EV (i.e. ETTR shot without blowing any highlight) and +2 give me the +4V sample. I use MLU and images match pixel by pixel even with my cheap tripod, it's very precise. Of course avoiding mirror flip could even be better but not necessary actually

Guillermo,

I uploaded two pairs of images, both 4 EV apart. They were shot with exposure bracketing, using a wired remote control, 2sec time delay; the tripod was on carpit. One pair shot with MLU, the other with MLU + live view.

http://www.panopeeper.com/Demo/MLU-2EV.CR2
http://www.panopeeper.com/Demo/MLU+2EV.CR2
http://www.panopeeper.com/Demo/LiveView-2EV.CR2
http://www.panopeeper.com/Demo/LiveView+2EV.CR2

The roof of the house can be taken for comparison, the leaves not, because of a slight breeze.

I wonder if you achieved better matching images with MLU than I did.

[Ray]

A final remark: the dynamic range and lesser noise of the 5D is a myth, compared to the 40D. There was a thread about this question. The 5D outputs about 3570 levels; in the nineth stop there are only seven levels.
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But the 5D has over 20% more pixels than the 40D. 3570x12.8/10.1=4524.

It's not clear to me what role the extra 2 bits of the 40D plays, but I recall John Sheehy mentioning that they don't appear to be producing any more real levels than 12 bits would produce.

[Panopeeper]

It's not clear to me what role the extra 2 bits of the 40D plays, but I recall John Sheehy mentioning that they don't appear to be producing any more real levels than 12 bits would produce.

It is not reasonable to reduce this question to the number of bits; it's not so simple.

The 5D creates about ~3570 levels. The 20D creates ~3970 levels. The 40D creates ~12800 levels at ISO 100, and ~15200 levels at higher, full stop ISOs.

This is about 3.5 times more at ISO 100 than that of the 5D. It is open to debate, how many of the 12800 levels of the 40D are really informative, but IMO it is clear, that the 5D is far underequipped with the 3570 levels.

On the practical side: I have no problem with carrying around lots of uninformative levels, they don't disturb me the least; however, the lack of levels in the shadows is an impediment. I would not exchange my 40D for a 5D based on image quality (based on other considerations even less).

Though it would be interesting to see a detailed, pixel-peeping comparison between the 40D and 5D, with the very same lens(es).

[Guillermo Luijk]

I wonder if you achieved better matching images with MLU than I did.

Probably no better, and no worse hehe. I will check that anyway.
When I have compared shots put in PS layers, the location of scene's elements was indistinguishable pixel by pixel.

[Guillermo Luijk]

It is not reasonable to reduce this question to the number of bits; it's not so simple.

The 5D creates about ~3570 levels. The 20D creates ~3970 levels. The 40D creates ~12800 levels at ISO 100, and ~15200 levels at higher, full stop ISOs.

This is about 3.5 times more at ISO 100 than that of the 5D. It is open to debate, how many of the 12800 levels of the 40D are really informative, but IMO it is clear, that the 5D is far underequipped with the 3570 levels.

On the practical side: I have no problem with carrying around lots of uninformative levels, they don't disturb me the least; however, the lack of levels in the shadows is an impediment. I would not exchange my 40D for a 5D based on image quality (based on other considerations even less).

Pano, you are talking about captured levels, but don't forget that interpolated levels are 16-bit on both machines, and photographs are made both from captured and interpolated levels.

Of course, if 40D levels are more precise than 5D's levels (4 times more precise to simplify), 40D's interpolated levels will also be more precise, so we could with no doubt say that 40D's images are more exact in defining the right level values.
But regarding tonal richness, after developing what you will have is:
- 40D: pixels with 1 channel taking 14 bit values, and 2 channels taking 16 bit values.
- 5D: pixels with 1 channel taking 12 bit values, and 2 channels taking 16 bit values.

Tonal precision in 40D is higher, but tonal richness (number of total different levels achieved) can be considered the same on both machines, and thus danger of posterization or banding due to lack of levels.
Moreover in the areas where the increased tonal precision could be really enjoyed (lowest f-stops) noise makes the image unusable so 40D cannot really take advantage of its increased no. of encoding bits.

In fact Leica's M8 RAW files are 8-bit. Yes, they are very cleverly distributed in a non-linear way, but they are 8 bit after all and even in the shadows are les precise (there is more gap between each pair of captured encoded levels) than 12-bit linear. Would you say Leica's M8 enconding produces noticeably lower quality images than any 12-bit linear camera?

I would exchange a 40D for a 5D if my priorities were strong bokeh and wide angle for example. In other words, FF.

[Panopeeper]

When I have compared shots put in PS layers, the location of scene's elements was indistinguishable pixel by pixel

Do you mind posting a pair of such shots?

My aim is to achieve raw pixel by pixel coverage; what you see are de-mosaiced pixels.

Tonal precision in 40D is higher, but tonal richness (number of total different levels achieved) can be considered the same on both machines, and thus danger of posterization or banding due to lack of levels

The number of tones in the resulting image is a non-issue. However, the de-mosaicing can create tones, but it can not create true details. If two pixels of the sensor can not differentiate between two slightly different tones of the subject, then that is lost, no matter how many tones you can fae by the de-mosaicing.

Moreover in the areas where the increased tonal precision could be really enjoyed (lowest f-stops) noise makes the image unusable so 40D cannot really take advantage of its increased no. of encoding bits

According to DCReview, the DR of the 40D is 9.1 stops in ISO 100 and ISO 200 (IMO this is incorrect, it is somewhat higher in ISO 200), and that of the 5D is 8.2 stops at ISO 100. The noise may be less with the 5D, but I doubt the correctness of those evaluations.

A higher dynamic range means, that the 40D does *need* more levels, and it can utilize them better.

Anyway, I would like to see a DR comparison with Jonathan's mehod, because the DPReview test regards only the noise, not the details.

Would you say Leica's M8 enconding produces noticeably lower quality images than any 12-bit linear camera?

Conditionally, yes. The M8 produces a crippled raw; it is good for nothing but change the white balance. When you need strong adjustments, the limits of the 8 bit will come forward.

Why do you think Leica's digital back has ***16*** bit depth? Is the digital back 256 times better than the M8?

exchange a 40D for a 5D if my priorities were strong bokeh and wide angle for example. In other words, FF.

Forget about the bokeh. No camera will make a lens suitable for good bokeh, no matter of the DoF. I don't know, what "strong" bokeh is, but if you like nice bokeh, you need a suitable lens, and that will not be an F4 lens.

[bjanes]

The number of tones in the resulting image is a non-issue. However, the de-mosaicing can create tones, but it can not create true details. If two pixels of the sensor can not differentiate between two slightly different tones of the subject, then that is lost, no matter how many tones you can fae by the de-mosaicing.

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The above statements are contradictory. Tones are a non-issue. Then by implication, an insufficient number of tones will limit rendering of detail. What did you mean to say?

Actually bit depth and resolution are not highly correlated. There is often little difference in resolution  between an 8 bit JPEG and a raw file rendered into 16 bits.

[Panopeeper]

The above statements are contradictory. Tones are a non-issue. Then by implication, an insufficient number of tones will limit rendering of detail. What did you mean to say?

Gullermo wrote:

regarding tonal richness, after developing what you will have is:
- 40D: pixels with 1 channel taking 14 bit values, and 2 channels taking 16 bit values.
- 5D: pixels with 1 channel taking 12 bit values, and 2 channels taking 16 bit values

We are talking about two kinds of levels: those sensed and those "created". Already the 256x256x256 tones are plenty in most cases, so the issue is not if the number of combinations from 3x12 bits are enough.

Any number of resulting levels does not help, when the levels of a channel are not enough to distinguish between details.

Actually bit depth and resolution are not highly correlated. There is often little difference in resolution  between an 8 bit JPEG and a raw file rendered into 16 bits.

I did not mention resolution. Different areas of an image may be indistinguishable because of lack of resolution OR because of lack of tonal levels.

An abstract example: half of the scenery consists of something of a constant color, the other half too, but slightly different color. If they are not different enough to be "seen as different" by the sensels, then the two halves appear identical - this has nothing to do with resolution.

[Ray]

An abstract example: half of the scenery consists of something of a constant color, the other half too, but slightly different color. If they are not different enough to be "seen as different" by the sensels, then the two halves appear identical - this has nothing to do with resolution.
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Interesting example. Would this be possible to demonstrate visually? I can appreciate that from a purely technical point of view, one could have the two halves of an image a very slightly different hue so that in order to technically (at the machine level) distinguish between them, you might need 14 bit or 16 bit capture instead of 12 bit, but would the eye be able to distinguish between such subtle differences that required this huge increase in the number of levels afforded by 14 or 16 bit processing?

We already know, for example, that the last stop of an ETTR exposure, in 12 bit, produces a far greater number of levels than the eye can detect, and maybe the penultimate stop too.