sk66
Advertiser
- Messages
- 8,759
- Name
- Steven
- Edit My Images
- Yes
A while ago I started questioning "why" there is "extra headroom" in a raw file that is not displayed on the camera. I knew that *all* histograms are based on a 0-255 scale for the sake of simplicity/consistency, but that's irrelevant...it's just a scale within which to define things.
I knew that the camera preview/histograms are based upon the thumbnail which is sRGB and that will have some effect on the histograms as opposed to a wider color space. But that shouldn't significantly affect the ability to interpret/define 0-0-0 or 255-255-255.
So I ran a test. I used an image borrowed from Cambridge in Color designed to push histograms. (note that the article itself is outdated and "wrong" in relation to current cameras)
I took a picture of the test image in raw with the camera's jpeg settings set to most accurately represent the displayed image.
Here are the histograms as they appeared on the camera. (the stripes are due to photographing a screen with a low refresh rate)
And here they are as they appear in PS (no edits performed, sRGB color space, LR looks similar).
There are huge discrepancies between them. And the camera luminance histogram looks more like a stack-up of the RGB histograms than an actual luminance histogram.
Some conclusions I came to.
The thumbnail may actually be optimized for the cameras display and only have 256 colors.
That some "perceptual bias" is being applied to the RGB curves based upon their percentage of contribution to the "percieved exposure." (30/59/11, RGB)
And that the REI (recommended slight underexposure) may also be being applied.
What this amounts to is the camera histograms are not "true" at all. They are "an interpretation" of the data displayed in accordance with what the manufacturer recommends you should do.
This is not just a Nikon thing (although Nikon does give a "disclaimer" for it). Canon's have similar issues. In fact, Canon's may be worse because at least some will report a color/highlight clipped if any of the levels hit ~250 instead of 255.
(Here's a link to similar Canon Specific 5D tests. Item 9)
I'm not an ETTR guy or "histogram reviewer;" I seldom even review images on the camera except when first setting up. And then I just judge the image itself.
Maybe that's why I found this so alarming. If I were to push this right using the luminance or highlight warnings I would have severely blown the blue channel. Or if I had been using the R/G channels I might have pulled the exposure back unnecessarily.
Granted, this is a "test image" and you are unlikely to encounter all of these simultaneously in real life, but it is quite possible to encounter one or two.
If anyone has any other explanations or thoughts, I'd love to hear them.
I knew that the camera preview/histograms are based upon the thumbnail which is sRGB and that will have some effect on the histograms as opposed to a wider color space. But that shouldn't significantly affect the ability to interpret/define 0-0-0 or 255-255-255.
So I ran a test. I used an image borrowed from Cambridge in Color designed to push histograms. (note that the article itself is outdated and "wrong" in relation to current cameras)
I took a picture of the test image in raw with the camera's jpeg settings set to most accurately represent the displayed image.
Here are the histograms as they appeared on the camera. (the stripes are due to photographing a screen with a low refresh rate)
And here they are as they appear in PS (no edits performed, sRGB color space, LR looks similar).
There are huge discrepancies between them. And the camera luminance histogram looks more like a stack-up of the RGB histograms than an actual luminance histogram.
Some conclusions I came to.
The thumbnail may actually be optimized for the cameras display and only have 256 colors.
That some "perceptual bias" is being applied to the RGB curves based upon their percentage of contribution to the "percieved exposure." (30/59/11, RGB)
And that the REI (recommended slight underexposure) may also be being applied.
What this amounts to is the camera histograms are not "true" at all. They are "an interpretation" of the data displayed in accordance with what the manufacturer recommends you should do.
This is not just a Nikon thing (although Nikon does give a "disclaimer" for it). Canon's have similar issues. In fact, Canon's may be worse because at least some will report a color/highlight clipped if any of the levels hit ~250 instead of 255.
(Here's a link to similar Canon Specific 5D tests. Item 9)
I'm not an ETTR guy or "histogram reviewer;" I seldom even review images on the camera except when first setting up. And then I just judge the image itself.
Maybe that's why I found this so alarming. If I were to push this right using the luminance or highlight warnings I would have severely blown the blue channel. Or if I had been using the R/G channels I might have pulled the exposure back unnecessarily.
Granted, this is a "test image" and you are unlikely to encounter all of these simultaneously in real life, but it is quite possible to encounter one or two.
If anyone has any other explanations or thoughts, I'd love to hear them.