[FRIAM] Kinks in perceptual space

Steve Smith sasmyth at swcp.com
Sun Mar 5 18:28:36 EST 2023 

Ed -

Great contribution.   Despite having lived in and around all of this 
from transmissive to reflective to emmissive CG hardware as well as 
cameras I have felt that some of the issues brought up in the paper were 
things that have long been swept under the carpet. I noticed the 
business you mentioned about having evaluated only luminance and 
*implying* that this might/could/should apply across chromaticity 
<https://en.wikipedia.org/wiki/Chromaticity>variations as well is 
tantamount to pulling many of the issues out from under the carpet then 
deliberately sweeping many of them right back under it?

I'm not sure how this new work isn't something like a re-affirmation or 
reformulation of the MacAdams work 
<https://en.wikipedia.org/wiki/MacAdam_ellipse> you reference, although 
the Just Noticeable Difference ellipses really just reference the 
local-metric of the CIE space they are registered on?

I haven't followed up on Anil's '82 JOSA paper but would like to...

My deepest dive into this space, especially related to 
color-compression, was the Faber-White-Saltzman work 
<https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/5130701> 
on color quantization in the early 90s?  My application was related to 
trying to exploit frame-to-frame quantization to (better) extend the 
limited NTSC color gamuts implied by video recording of the era (vs the 
64M color space we were getting on our 16mm film recorders of the time).



On 3/5/23 11:21 AM, Angel Edward wrote:
> Steve,
>
> Thanks for the post. I haven’t been following the research in color 
> for a long time although it remains one of the areas I love to talk 
> about in my books and lectures.
>
> The paper is really interesting although I’m not sure how the result 
> could be used in areas such as compression since both small and large 
> differences in color are important. Maybe on the user side but not on 
> the transmission or storage side. The Fast Company article shows a 
> superficial understanding of color spaces at times and thus 
> exaggerates the potential results of the research.
>
> I have a couple of potential issues with the paper that I thought 
> would have been brought up by reviewers. Early the paper, there is 
> statement that seems to say that RGB is what the cones in our eyes 
> sense. Perhaps it's just a poorly stated sentence but the there types 
> of cones do not measure r, G and B in a 1 to 1 way. The three types 
> have peaks in the Green, between Green and Yellow, and in the Blue. In 
> addition, we less than 10% of cones are blue sensitive (and these tend 
> to be on the periphery of the retina). The standard NTSC RGB system 
> was based on the available  technology and not on perception. 
>  Luminance (L in Lab, Y in XYZ) is mostly Green and Yellow. What makes 
> things more complex is that we are more sensitive to  small changes in 
> color (MacAdams ellipsoids of Just Noticeable Differences) in the blue 
> and least sensitive in the Green.
>
> I would have not pointed out the above except that I was worried that 
> the experiment was done totally on luminance, changing L* with 
> a*=b*=0. I would have found the paper more convincing if the measure 
> was applied to changes in chromaticity in the experiment.
>
> We used to worry about these issues way back in the 70’s when I was 
> working with my friend Anil Jain at the USC Image Processing 
> Institute. One problem then finding color maps for compressing a color 
> image form 3 bytes/pixel to 1 byte/pixel and for pseudo coloring 
> grayscale images. The problem was to find a map that in which each 
> step was perceptually equal. Anil did a paper that appeared in the 
> JOSA in 82 using geodesics in a perceptual color space. The problem 
> with the result was that the colors he got were really ugly compared 
> to the usual thermal map using cool colors (blues and greens) going to 
> hot colors (yellows and reds).
>
> Ed
> __________
>
> Ed Angel
>
> Founding Director, Art, Research, Technology and Science Laboratory 
> (ARTS Lab)
> Professor Emeritus of Computer Science, University of New Mexico
>
> 1017 Sierra Pinon
> Santa Fe, NM 87501
> 505-984-0136 (home)edward.angel at gmail.com
> 505-453-4944 (cell) http://www.cs.unm.edu/~angel
>
>> On Mar 4, 2023, at 4:22 PM, Steve Smith <sasmyth at swcp.com> wrote:
>>
>> This may or may not relate to the current threads about mind v body, 
>> perceptual nature of reality, etc that we have been flogging, but it 
>> is a topic I lived in and around for most of my career and found it 
>> both familiar/compelling and a little disturbing:
>>
>> The general topic is the non-Reimannian nature of perceptual color 
>> spaces.
>>
>> The broadly accepted non-Euclidean color spaces described by the CIE 
>> formulations (1931 and 1976) has been widely accepted while the 
>> RGB/CMYK/HSV Euclidean approximations are what most folks use for 
>> pretty good practical reasons (particular the conveniences of 
>> tristimulus/process color specification and synthesis).
>>
>> This recent (1 year old) publication work by some LANL folks was 
>> shoved in my face/space recently (as a correlate to the problems we 
>> have been working with on trying to understand the underlying space 
>> of abstract high dimensional (very non-linear) problems such as 
>> ensemble steering/exploration in the World3 model.   Our favored 
>> method (of the moment) is a variant of tSNE 
>> <https://en.wikipedia.org/wiki/T-distributed_stochastic_neighbor_embedding><https://en.wikipedia.org/wiki/T-distributed_stochastic_neighbor_embedding>which 
>> prefers a locally accurate metric over a global one.
>>
>> The LANL work on this non-Reimannian color space:
>>
>>     https://www.pnas.org/doi/full/10.1073/pnas.2119753119
>>
>> A popular article about that work:
>>
>>     https://www.fastcompany.com/90780869/it-could-take-20-more-years-for-scientists-to-truly-understand-color
>>     <https://www.fastcompany.com/90780869/it-could-take-20-more-years-for-scientists-to-truly-understand-color>
>>
>> I'm guessing this (at least) crossed Ed Angel's awareness, perhaps 
>> there are a few others here who care about this level of 
>> detail/abstraction on color/perceptual spaces?  Frank is probably a 
>> lot more up on the nuances of (non) Reimannian manifolds than I ever 
>> will be...  I don't know if this represents an interesting example of 
>> the utility of such?
>>
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