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funny codec named “None”
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[gary adcock] “humans do not have the visual acuity to see EVEN 1024 levels of gray at one time.”
Not so sure about that. I’ve read about people who are developing HDR monitors. While the human eye definitely can’t detect 0-1024 black to white simultaneously, I think within a limited range, like a low-light environment after your eyes adjust, you can see shadow detail beyond what 10-bit is capable of. I mean, until one can’t distinguish video from looking out a window…
Sean
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[Gary Adcock]: “YUV video is more analogous to the ICE-LAB colorspace than the RGB space, and if you did actually know these color spaces you would understand that RGB info is indicating how many colors as Chroma that can be recorded while YUV bit depth is determined by levels of Luma that can be captured.”
Sorry Gary, but I actually do know some color science, and RGB makes a hilariously distorted color space in the sense that distances in this space have hardly any relation to perceptual distances between colors. Thus the number of colors determined by the number of bits of R,G,B is no indication of the richness of the color gamut. On the other hand LAB and LUV spaces are attempts (by CIE in 1976) to model the perceptual color space. The number of bits of L,U,V does indicate the richness of the color gamut.
Do not confuse ‘chroma’ with color. Color space is 3-dimensional, whether the dimensions are R,G,B or L,U,V. If you doubt that luminance is a dimension of color then explain why a brown and a yellow can be different colors despite having identical chroma. -
Rafael, I beg to differ. Compressor converts (transforms) clips from one codec to another. I drop in DV coded material and Compressor spits out None coded material. The DV codec didn’t exist when the None codec was written, so Apple Compressor must be responsible for these results. And I’m sure there’s a flaw in the way Compressor makes None when “16 Colors” (4-bit depth) and quality less than 50 are selected. A grey scale in the original becomes a grey scale EXCEPT FOR one light brown stuck in the scale where you’d expect a dark grey. This is either a boner or a joke, and it makes me wonder about Apple’s competence or seriousness.
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[gary adcock]: “humans do not have the visual acuity to see EVEN 1024 levels of gray at one time.”
This remark overlooks the fundamental weakness of linear coded intensity levels. Yes, it is true that humans can’t discriminate 1024 levels of gray at one time. But the 1024 levels 0,1,2,… 1023 used in linear coded video do allow some discriminations.For example, while it is absolutely impossible to see the difference between the 1022 level and the 1023 level, or even between the 500 level and 501 level, it is easy to see the differences in the first 10 or 20 steps. (See how CIE Publication 15 defines Y* to understand this.) This is why linear coded intensity is wasteful of bandwidth. The linear steps are much too close at the high end and not close enough at the low end.
Fine tonal discrimination is even easier when one tone is moving over the other. It is because of motion that digital video requires closer tonal spacing than digital still images require.
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[Dennis Couzin] “Do not confuse ‘chroma’ with color. Color space is 3-dimensional, whether the dimensions are R,G,B or L,U,V. If you doubt that luminance is a dimension of color then explain why a brown and a yellow can be different colors despite having identical chroma.”
That’s clear. You may have to pixels with the same Cb’-Cr’ values but if the value of Y’ is different, you will get different RGB values in both pixels. So two different colors.
rafael(and here some clips for the friends: https://www.vimeo.com/2694745 )
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[Dennis Couzin] “Do not confuse ‘chroma’ with color. Color space is 3-dimensional, whether the dimensions are R,G,B or L,U,V.”
But that would not be true in YUV, where Luma info and Chroma were originally designed to operate as a separate but combined entity, and this is where I believe the confusion lies.
If you understand color as you say then you know that the space, monitoring and control in video is vastly different that in the Color spaces you are referring to.
I was accurate in my original comment that the YUV colorspace in video most closely mimics what is the working print space called LAB, I use LAB color regularly to show how the signal paths do not diverge until output by showing how minor changes (IE: a Gaussian blur) to the A /B channels in LAB have little effect on the overall image color or quality, yet a change to Luma channel has a drastic effect rather quickly.
The LUV and RGB color spaces you mention function under differing rules than does the SMPTE spec for YUV video.
In the Video Space Chroma is defined as the underlying color phase and amplitude and that signal was originally a completely separate signal than the B&W signal (as Luma Only) this is exemplified by the
YCbCr (as digital) color model defined as YPbPr (as analog) is converted from the base signal, is split into three base components, where
Y carries luma (brightness) information.
PB carries the difference between blue and luma (B − Y).
PR carries the difference between red and luma (R − Y).Since “color space” is a more specific term for a certain combination of a color model plus a color mapping function you can see that in video these signals are carried over wire in different form than what is done with other types of transmission.
gary adcock
Studio37
HD & Film Consultation
Post and Production WorkflowsInside look at the IoHD
https://library.creativecow.net/articles/adcock_gary/AJAIOHD.php -
[Dennis Couzin] “This remark overlooks the fundamental weakness of linear coded intensity levels. Yes, it is true that humans can’t discriminate 1024 levels of gray at one time.”
it overlooks nothing, you even agree that the statement is correct, I just chose not to going into minutiae without knowing whom I was talking to.
gary adcock
Studio37
HD & Film Consultation
Post and Production WorkflowsInside look at the IoHD
https://library.creativecow.net/articles/adcock_gary/AJAIOHD.php -
Gary Adcock, what you wrote was: “the limit for a “video” signal stands at what it is and I do not foresee it changing in my lifetime since humans do not have the visual acuity to see EVEN 1024 levels of gray at one time.” The logic of this statement presumes that since humans can’t distinguish 1024 grey levels they can’t distinguish ANY of the steps in the linear 1024 grey levels. They can. Linear vs. nonlinear scales is fundamental, not a minutia, for digital video.
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Rafael, that was exactly what I meant.
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[Gary Adcock]: “YUV video is more analogous to the ICE-LAB colorspace than the RGB space, and if you did actually know these color spaces you would understand that RGB info is indicating how many colors as Chroma that can be recorded while YUV bit depth is determined by levels of Luma that can be captured.”
It was in response to this erroneous statement that I wrote “Do not confuse ‘chroma’ with color.”
RGB does NOT indicate “how many colors AS CHROMA can be recorded”. Chroma is 2-dimensional, and RGB gives a 3-dimensional indication. Indeed RGB contains the (1-dimensional) luminance information as well as the (2-dimensional) chroma information. When there are 8 bits for each of R,G,B there are 2^24 COLORS represented. There are not 2^24 CHROMA represented. I can only repeat: do not confuse ‘chroma’ with color.
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