New article on color management

Started Apr 26, 2013 | Discussions thread
Great Bustard
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OK, this is good stuff.
In reply to Hugowolf, Apr 29, 2013

Hugowolf wrote:

gollywop wrote:

Great Bustard wrote:

What I'm asking, I guess, is if 16 bit sRGB will ever have any practical advantage over a larger 16 bit colorspace due to the finer gradations of the colors it does represent.

Well, I have certainly encountered significant posterization in large expanses of blue skies under aggressive tone mapping when PP-ing an 8-bit sRGB jpeg.  This is not an uncommon experience.

And, unfortunately, once an image starts life as an 8-bit image, you don't gain a heck of a lot just converting to 16 bits; all those gradations in between don't suddenly get created.  If you're going to use 16-bits with sRGB, you want to shoot raw and process with 16-bits from the outset.

As to just what color differences humans can see, and how fine practical gradations can be, we humans are apparently much more sensitive to small shifts in blues than reds, and more in reds than greens. So the whole notion of JND (just noticeable difference) in color is very wavelength related. Clearly going to 16-bits is a huge boost. It gives a 256 fold increase in the number of divisions over 8-bits, and none of the color spaces is anywhere nearly 256 times larger in linear dimension.

You can get an idea of all this from the MacAdam ellipses:

http://en.wikipedia.org/wiki/MacAdam_ellipse

but beware in assessing the diagram they give there that they have exaggerated the sizes of the ellipses ten fold.

Interesting as it may be (MacAdam et al) it doesn’t address metameristic differences: that colors may be indistinguishable within their range, but may produce visual differences when placed next to other colors.

That's fascinating.  You mean I can put two colors next to each other, not see a difference, but put those two colors next to a different color, and then notice a difference?  Trippy!

And on the use of either or both 16 bit and a large space like ProPhotoRGB, surely the concern is not with final reproduction (print, screen, projection) but with the ability to manipulate without clipping during editing – working space as opposed to output space. There are many operations which when performed under a space as restrictive as sRGB, could cause a push out of gamut during operations, which could (had they been in a more expansive space) subsequently landed them back in the expected output gamut.

OK, so if you have an sRGB monitor, can you *accurately* edit the photo in PPRGB or aRGB?  Or might there be problems when converting from PPRGB to sRGB as gollywop hinted at?

In other words, it seems like you're saying there's an advantage to work in a wider colorspace, like PPRGB or aRGB, even if your final colorspace is sRGB.

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