Re: On monochrome images and metamerism, or not.
Re: On monochrome images and metamerism, or not.
- Subject: Re: On monochrome images and metamerism, or not.
- From: Marco Ugolini <email@hidden>
- Date: Sun, 20 Jun 2010 22:49:33 -0400 (EDT)
Simon ONeill wrote:
>Hi Ernst,
>
>I have observed differences in a typical (good colour vision) observer's ability to distinguish between colour shifts near the neutral grey axis and between more saturated colours. I did some tests which showed people unable to distinguish easily between DeltaE(76) of 5.0 for saturated colours (near the gamut edge of an inkjet printer) whereas a DeltaEab of 0.5 is typically visible when near the neutral (grey) axis. This was a very small sample, but was intended to demonstrate (as it did) that the Lab space is not truly "perceptually uniform".
I think that it's more the case that the DeltaE 76 formula is not very good at indicating degrees of color difference as we (humans) actually see them. Use DeltaE 2000 instead (which is weighted for many factors that intervene in human vision), and you may notice that what is a 5 in DeltaE 76 actually can become much smaller, more closely reflecting the actual viewer's experience.
Personally, I think DeltaE 76 ought to be "retired". Its formula is very primitive, and handles the Lab space as if it were perfectly linear and uniform, which it is NOT, as you rightly remind us. DeltaE 2000 does a much better job of accounting for that non-uniformity, though it's still not "perfect". (The DeltaE 2000 formula is already fairly complex, but a "perfect" color difference formula would probably demand an ungodly degree of complexity.)
Marco Ugolini
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