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Author Topic: Lightroom 2012 Exposure control different from PS adjustment layer  (Read 5958 times)
Jim Kasson
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« Reply #60 on: April 24, 2013, 06:27:40 PM »
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A while back in this thread, before Eric Chan pointed out that there were two image processing pipelines in Lightroom and that all my integer TIFF testing wasn't really relevant to raw processing, some of you asked about different error measures than CIELab Delta-E, specifically something related to hue errors. These color difference measures can get quite complicated. Here's an example. I can, if there's sufficient interest, implement some of these more complex, and presumably, accurate, measures, but I'll present here just the basics. In the precious post, I presented the Delta-E curves.

Here's a set of Delta-H curves, the basic CIEL*a*b* difference metric that measures hue error:

 

Like Delta-E, Delta-H can't go negative.  

Here are the Delta-C curves, which measures differences in what's called "metric chroma", the radial distance from the grey axis:

 

Delta-C is positive if the test color is more chromatic than the reference, and negative if the test color is less chromatic than the reference. The fact that there's a tendency towards positive Delta-C indicates that making positive LR exposure adjustments tends to make the colors more chromatic than they should be. You can see that from the scatter plots as well.

If you look at the numbers in the Delta-H and Delta-C plots, you can see that most of the chromaticity error comes from too much chroma, not from hue shift.

And, although it's not a CIELab standard, I like to look at hue angle errors. The big potential problem with looking at hue angle alone is that errors near the grey axis, where they are inconsequential, can have the same value as errors in highly chromatic colors, where they are significant. Still, it gives indications of any possible hue shift bias. Here is the hue angle data:

 

Pretty symmetrical.

Jim
« Last Edit: April 24, 2013, 06:30:13 PM by Jim Kasson » Logged

John Cothron
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« Reply #61 on: April 24, 2013, 06:59:14 PM »
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That's interesting Jim.  In most of the tests I ran, granted far more simplistic than what you have put together here, I saw the chroma decrease as I pushed the exposure from under-exposed to normal exposure.  Example being the Bright Yellow, which went bluer as a result of pushing the exposure, or the bright purple... for example.  Your data covers 121 different patches however, so the sample size may be more indicative.
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Jim Kasson
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« Reply #62 on: April 24, 2013, 07:13:42 PM »
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I just can't stop coding, or, in this case, downloading Matlab code put up by these people.

Here are the results using the The CIEDE2000 Color-Difference Formula:



The errors seem much smaller. I have no experience with this formula, so I don't know quite what to make of the results.

Jim
« Last Edit: April 24, 2013, 07:31:46 PM by Jim Kasson » Logged

John Cothron
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« Reply #63 on: April 24, 2013, 07:18:02 PM »
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lol@coding binge
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Jim Kasson
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« Reply #64 on: April 24, 2013, 07:19:18 PM »
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I saw the chroma decrease as I pushed the exposure from under-exposed to normal exposure.  Example being the Bright Yellow, which went bluer as a result of pushing the exposure, or the bright purple... for example. 

John, it's possible that you are describing hue shift, not a change in chroma. It's hard for me to tell because of the example you chose. Do you mean the the bright yellow moved towards the grey axis?  That means it got less chromatic. However, if the yellow acquired a color tinge, that's a hue shift.

Jim
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« Reply #65 on: April 24, 2013, 07:24:39 PM »
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John, it's possible that you are describing hue shift, not a change in chroma. It's hard for me to tell because of the example you chose. Do you mean the the bright yellow moved towards the grey axis?  That means it got less chromatic. However, if the yellow acquired a color tinge, that's a hue shift.

Jim

I'm referring to chroma.. as in the case of the yellow which measures significantly "bluer" with the pushed exposure.  The hue shift (red/green) was very small.  The b value dropped from 114 to 109 or so.  

Sample #16 in the chart I posted.
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Jim Kasson
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« Reply #66 on: April 24, 2013, 07:50:01 PM »
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I'm referring to chroma.. as in the case of the yellow which measures significantly "bluer" with the pushed exposure.  The hue shift (red/green) was very small.  The b value dropped from 114 to 109 or so.  

Sample #16 in the chart I posted.

Gotcha. You're absolutely right. I wouldn't have said it that way, because it makes my head hurt to think about a more bluish yellow or a more greenish red.

Jim
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John Cothron
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« Reply #67 on: April 24, 2013, 08:01:19 PM »
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lol.. I understand.  I'm just basing my phrasing on the Lab coordinates.
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