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Author Topic: Lightroom 2012 Exposure control different from PS adjustment layer  (Read 9820 times)
Jim Kasson
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« Reply #20 on: April 18, 2013, 02:12:32 PM »
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Your simulations are quite sophisticated and interesting. You might want to apply them to PV2010 as well.

Bill, I did a run with PV2010. The chromaticity errors associated with the 1 through 4 stop pushes on the middle luminance tones are roughly the same as with PV 2012;

The plots are here.

I'm thinking about computing the chromaticity delta-Es and summing them as a measure of overall accuracy in the chromaticity plane. In order to make it fair, I'll have to calibrate out the effects of my not getting the mean L* values back to exactly 50 in each of the pushes.

Jim
« Last Edit: April 18, 2013, 02:21:18 PM by Jim Kasson » Logged

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« Reply #21 on: April 18, 2013, 04:44:02 PM »
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I'm thinking about computing the chromaticity delta-Es and summing them as a measure of overall accuracy in the chromaticity plane. In order to make it fair, I'll have to calibrate out the effects of my not getting the mean L* values back to exactly 50 in each of the pushes.

I did that work this afternoon. Well, almost. I decided to compute the average total error over the 121 patches, not just the chromaticity error. Here's the result:



To get the curves, I corrected all the values in the sample images by dividing them by the ratio of the mean of the luminance values in the sample image and the mean of the luminance values in the test (exposed for a 0 EV push) image. That corrects for Exposure slider settings that aren't quite right.

Jim

« Last Edit: April 18, 2013, 04:56:07 PM by Jim Kasson » Logged

bjanes
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« Reply #22 on: April 20, 2013, 05:52:21 AM »
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Good idea, Bill. I'll do that.

I don't think LR uses a camera profile for the files I'm importing.

The image with no LR Exposure corrections looks like the image that I imported into LR ins the first place, which is what makes me think that there is no camera profile applied by LR. This also makes sense to me, since you wouldn't want LR to do something to a finished TIFF image that you imported into LR just to use it's cataloging ability.

Does that make sense to you?

Jim

Jim,

Yes, it does. When I brought the subject of camera profiles in the context of TIFFs, I wasn't thinking clearly. Rereading Eric's post confirms that they would not be used with TIFFs. Demosaicing and conversion of the camera primaries to the working space have already been performed at the TIFF stage.

Regards,

Bill
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FranciscoDisilvestro
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« Reply #23 on: April 20, 2013, 06:48:43 AM »
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As others have noted, PV 2003 or 2010 are much more linear (similar to Ps's Exposure) as you increase the Exposure control (a la in-camera ISO) but a side effect is that when individual color channels start to clip you get unsightly hue shifts (e.g., blue skies become cyan) and a sudden loss of color detail. 

The linear behavior of a digital sensor is a physical reality but not necessarily a desirable visual characteristic.

What about changing the baseline exposure in the DNG profile? Will it behave like a linear adjustment as in-camera ISO?
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« Reply #24 on: April 20, 2013, 07:57:55 AM »
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The issue with using ACR/LR to test with normal TIFF files created externally is that ACR/LR assumes they are output-referred (i.e., already tone mapped).  Thus it is true that the Exposure control may not be linear and have unintended side effects, because ACR/LR has to make a guess as to the scene-to-output referred mapping. 

If you want to use TIFFs for doing this type of testing I would suggest you use floating-point TIFFs (not 16-bit integer) or use linear DNG.
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madmanchan
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« Reply #25 on: April 20, 2013, 07:58:37 AM »
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Put another way:  the current ACR/LR testing path on your TIFF files is going thru a different image processing path than compared to processing raw files.
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bjanes
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« Reply #26 on: April 20, 2013, 07:59:22 AM »
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I did that work this afternoon. Well, almost. I decided to compute the average total error over the 121 patches, not just the chromaticity error. Here's the result:



To get the curves, I corrected all the values in the sample images by dividing them by the ratio of the mean of the luminance values in the sample image and the mean of the luminance values in the test (exposed for a 0 EV push) image. That corrects for Exposure slider settings that aren't quite right.


Jim,

A delta E of 6 is significant. I'm no color expert, but the details of the calculation would be of interest since delta E includes luminance, chroma, and hue as briefly explained by Norman Koren in his Colorcheck documentation (that is about all I know about the subject). It is well documented that ACR does increase saturation as exposure is increased and this is by design, as it is preferred by many users. However, a shift in hue is unwelcome by most.

Regards,

Bill
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Jim Kasson
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« Reply #27 on: April 20, 2013, 09:47:44 AM »
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. I'm no color expert, but the details of the calculation would be of interest since delta E includes luminance, chroma, and hue...

Given two values in CIEL*a*b*, L1, a1, b1, and L2, a2, b2, the CIEL*a*b* Delta-E is:

sqrt((L1-L2)^2 + (a1-a2)^2 + (b1-b2)^2)

Stated in words, it is the distance in three-space between the two values plotted in Cartesian coordinates.


It is well documented that ACR does increase saturation as exposure is increased and this is by design, as it is preferred by many users. However, a shift in hue is unwelcome by most.

There is no measure of saturation in CIEL*a*b*. There are good technical reasons for this, which I won't go into unless requested to do so. There is one in CIEL*u*v*, but Photoshop doesn't support that system, and most photographers aren't familiar with it. Some have suggested that a saturation measure for Lab might look like this (dropping the stars):

PseudoSat = Sqrt(a^2 + b^2) / L
My tests indicated that Lightroom does not increase this quantity upon increasing exposure. It does -- and should -- increase chroma, defined as:

Chroma = Sqrt(a^2 + b^2)

If you imagine CIELab in cylindrical coordinates instead of Cartesian ones, luminance goes up and down, hue is the angle, and chroma is the radius.

If you look at the actual color plots, you can see that there is no general chroma or hue shift, just shifts that affect both.

Eric has put my testing methodology into question, and I'm going to have to fall back and regroup.

Jim
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bjanes
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« Reply #28 on: April 20, 2013, 10:08:32 AM »
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Given two values in CIEL*a*b*, L1, a1, b1, and L2, a2, b2, the CIEL*a*b* Delta-E is:

sqrt((L1-L2)^2 + (a1-a2)^2 + (b1-b2)^2)

Stated in words, it is the distance in three-space between the two values plotted in Cartesian coordinates.


There is no measure of saturation in CIEL*a*b*. There are good technical reasons for this, which I won't go into unless requested to do so. There is one in CIEL*u*v*, but Photoshop doesn't support that system, and most photographers aren't familiar with it. Some have suggested that a saturation measure for Lab might look like this (dropping the stars):

PseudoSat = Sqrt(a^2 + b^2) / L
My tests indicated that Lightroom does not increase this quantity upon increasing exposure. It does -- and should -- increase chroma, defined as:

Chroma = Sqrt(a^2 + b^2)

If you imagine CIELab in cylindrical coordinates instead of Cartesian ones, luminance goes up and down, hue is the angle, and chroma is the radius.

If you look at the actual color plots, you can see that there is no general chroma or hue shift, just shifts that affect both.

Eric has put my testing methodology into question, and I'm going to have to fall back and regroup.

Jim


Jim,

Did you look at Norman's writeup? He does separate total delta E into components. I will have to study the details.

Just for fun, I exposed a Colorchecker under Solux illumination at nominal exposure, and at -1, -2, -3, and -5 EV. I then used ACR 7.4 with PV2012 at default settings and the Adobe Standard profile and looked at the results with Imatest. I adjusted exposure so that the white patch was 236 in AdobeRGB (the nominal value according to Bruce Lindbloom's measurements). The -4 EV exposure on the camera LCD looked quite dark and the chart was hardly recognizable, but the resulting images after correction looked quite good and the color values were hardly different with increasing ACR correction. According to these tests, ACR works well for underexposed images, but the results do show relatively large constant color errors and I should probably use the DNG profile editor.

Nominal


1 stop underexposed


2 stops underexposed


3 stops underexposed


4 stops underexposed


Tabular Results


Regards,

Bill
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Jim Kasson
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« Reply #29 on: April 20, 2013, 10:27:41 AM »
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Did you look at Norman's writeup? He does separate total delta E into components.

Yes, there are additional standard color differences. I thought about doing the chrominance delta E, or DeltaEab, and I'm glad that I didn't now, since Eric has said that my test methodology is flawed because I used TIFFs.

Just for fun, I exposed a Colorchecker under Solux illumination at nominal exposure, and at -1, -2, -3, and -5 EV. I then used ACR 7.4 with PV2012 at default settings and the Adobe Standard profile and looked at the results with Imatest. I adjusted exposure so that the white patch was 236 in AdobeRGB (the nominal value according to Bruce Lindbloom's measurements). The -4 EV exposure on the camera LCD looked quite dark and the chart was hardly recognizable, but the resulting images after correction looked quite good and the color values were hardly different with increasing ACR correction. According to these tests, ACR works well for underexposed images, but the results do show relatively large constant color errors and I should probably use the DNG profile editor.

Good work, Bill! I had been resisting using actual camera images because of the extra noise introduced, the difficulty in making the measurements, and the greater possibility of tester (that would be me) error. I think I'm going to have to bite the bullet and stop using the synthetic images. It would be different if I had a way to make DNG files (or, even better, NEF files) but I don't.  

I wouldn't worry about the color errors that are constant throughout the image set. We' re trying to find out how useful LR is for the pushes we're likely to see with Unity Gain ISO exposure techniques, not how accurate the camera is in general at capturing accurate color.

In order to see how the color errors vary with exposure without looking at the effects of the overall errors, is is possible for you to compare just the values of the patches in the various images without looking at how far away they are from the original?

Thanks for going to the trouble of doing this testing!

Jim
« Last Edit: April 20, 2013, 10:32:06 AM by Jim Kasson » Logged

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« Reply #30 on: April 20, 2013, 12:08:41 PM »
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The issue with using ACR/LR to test with normal TIFF files created externally is that ACR/LR assumes they are output-referred (i.e., already tone mapped).  Thus it is true that the Exposure control may not be linear and have unintended side effects, because ACR/LR has to make a guess as to the scene-to-output referred mapping.  

If you want to use TIFFs for doing this type of testing I would suggest you use floating-point TIFFs (not 16-bit integer) or use linear DNG.

Eric, although all my Matlab calculations are done with double precision floating point images, imwrite can't write a floating point TIFF file. I'm not sure that would solve the problem anyway, since they'd still be viewed by LR as output-referred. I don't have any tools that can write DNG files. I think I'm going to have to stop using synthetic images and suffer all the tribulations of using real camera images.

I can use a screen target or a printed target. I think the screen target would be more accurate, but I'd either have to defocus or do a lot of averaging. If I defocused, I couldn't vary the exposure by varying the f-stop, because the lens circle of confusion would change over the series. Actually, now that I think about it, I can't vary the exposure by changing the aperture, because that will change the light falloff away from the lens axis. Using exposures of faster than 1/30 on an LCD monitor is unsafe in terms of repeatability, but I could go from a second to 1/30, and that will give me five stops.

I could make an exposure at 1 second at the unity gain ISO, then decrease the exposure progressively: 1/2, 1/4, 1/8, 1/15, 1/30. As a control, I could do the same series increasing the ISO one stop for every change in shutter speed. Then I could bring the raw files into LR, develop them, and export them as TIFFs. Then I can read them into PS, convert them to Lab, and save them. Then I could bring them into Matlab, do filtering (probably with an nxn kernal where all the values are 1/n^2), resampling, correction for actual in-camera exposure errors, correction for Exposure adjustment setting errors (those two are the same correction), measurement, error computation, and statistics calculation.

Does that methodology make sense to you?

Jim
« Last Edit: April 20, 2013, 12:11:12 PM by Jim Kasson » Logged

bjanes
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« Reply #31 on: April 20, 2013, 02:00:23 PM »
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Yes, there are additional standard color differences. I thought about doing the chrominance delta E, or DeltaEab, and I'm glad that I didn't now, since Eric has said that my test methodology is flawed because I used TIFFs.

Good work, Bill! I had been resisting using actual camera images because of the extra noise introduced, the difficulty in making the measurements, and the greater possibility of tester (that would be me) error. I think I'm going to have to bite the bullet and stop using the synthetic images. It would be different if I had a way to make DNG files (or, even better, NEF files) but I don't.  

I wouldn't worry about the color errors that are constant throughout the image set. We' re trying to find out how useful LR is for the pushes we're likely to see with Unity Gain ISO exposure techniques, not how accurate the camera is in general at capturing accurate color.

In order to see how the color errors vary with exposure without looking at the effects of the overall errors, is is possible for you to compare just the values of the patches in the various images without looking at how far away they are from the original?

Thanks for going to the trouble of doing this testing!

Jim

Jim,

I repeated the tests with PV2010 using a linear tone curve and a profile created with Xrite Passport. In previous testing, I have found that PV2010 with a linear profile gives the most accurate results.

The graphical results show values for each patch of the Colorchecker. Differences lying radially from the white point indicate chroma differences, whereas hue shifts show a skew from the radial direction. The results are also shown in tabular form, using CIEDE2000 terms. The Delta E ab includes luminance. The Delta C omits luminance and the Delta C (corr) includes correction for chroma boost. The 4 stop push does not affect the colors that much. Is this the information you wanted?

Regards,

Bill

PV2010 Passport Profile, Nominal Exposure


PV2010 Passport Profile, 4 Stop Push


Tabular Results
« Last Edit: April 20, 2013, 03:03:13 PM by bjanes » Logged
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« Reply #32 on: April 20, 2013, 02:10:04 PM »
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If you're wanting to look at Hue differences, Lch equations would be much more useful (Luminance, chromaticity, hue).  Delta E for Lab coordinates are useful, but you have to look at the specific coordinates to determine where the shift is taking place, as the axix for Lab is always expressed as L(lightness,darkness), a(red,green), and b(yellow,blue).  Lch on the other hand, is just what it says.  Chroma in a blue results in the c expressing yellow/blue, whereas in a red the c will be expressing red/green shift.  If you want a 1 number equation that works pretty well at giving you a number that correlates with human "satisfaction" of of color difference, take a look at the CMC equation, preferably weighted with a 2:1 ration on the chroma and hue, meaning the hue "matters" twice as much as the chroma of a color where humans detecting color difference is concerned.  In general, a CMC color difference of 1.0 unit or so is very close visually whereas 1.0 DE Cielab can be objectionable dependent on which axis is showing the majority of the difference.

I believe this is the topic you guys are discussing regarding how the exposure slider is working in Lr PV2012.

***I understand part of this is how Lr behaves in comparison to Ps, which is something I didn't do.
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« Reply #33 on: April 20, 2013, 03:09:05 PM »
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If you're wanting to look at Hue differences, Lch equations would be much more useful (Luminance, chromaticity, hue).  Delta E for Lab coordinates are useful, but you have to look at the specific coordinates to determine where the shift is taking place, as the axix for Lab is always expressed as L(lightness,darkness), a(red,green), and b(yellow,blue).

John, when I redo the tests with a real camera instead of a simulated one, I'll present the results several different ways, since there is apparently interest in that. I've always found that these measures are best supplemented by looking at the actual 2D and 3D shifts. I presented both 2D and 3D plots earlier, as well as links to more. I think that I'll at least continue to present the links. I'm conscious of the fact that presenting a slew of graphs on this forum may be way more than most people want to see.

There is a problem with presenting 2D and 3D scattergrams with the real camera results. If not calibrated out, the grid for the "no push" or reference image will not be regular. I'm thinking that the way to handle that is to calculate the shifts from the reference image, apply those shifts to the canonical image which created the target (and has a regular grid in CIEL*a*b*), and plot that. Does anyone have a comment of that approach?

Jim
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« Reply #34 on: April 20, 2013, 03:33:42 PM »
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John, when I redo the tests with a real camera instead of a simulated one, I'll present the results several different ways, since there is apparently interest in that. I've always found that these measures are best supplemented by looking at the actual 2D and 3D shifts. I presented both 2D and 3D plots earlier, as well as links to more. I think that I'll at least continue to present the links. I'm conscious of the fact that presenting a slew of graphs on this forum may be way more than most people want to see.

There is a problem with presenting 2D and 3D scattergrams with the real camera results. If not calibrated out, the grid for the "no push" or reference image will not be regular. I'm thinking that the way to handle that is to calculate the shifts from the reference image, apply those shifts to the canonical image which created the target (and has a regular grid in CIEL*a*b*), and plot that. Does anyone have a comment of that approach?

Jim

Jim,

First I'll say I haven't fully digested what you have already done, which on the surface appear to be a lot of work, and accurate work.  I only wanted to throw my .02 out there in reference to the color equations.  I'm not even sure what options for color equations you have in some of the software you are using (I haven't used those personally).  I think however, if the point of this exercise is to establish how the exposure sliding is operating with respect to rolling off highlights and/or the color shifts that result, that you will be well served to (in addition to the charts) present the data with actual Lab coordinates.  I realize you can't do that for everypoint or color in an image, but you could probably choose 2 o3 three primary colors, and perhaps 2 or 3 spots with the same colors but lower chromaticity.   I could be way off base here I'm just sort of speculating based on how some other things work but...

I suspect where you will see the largest shift is in the higher chroma areas that are approaching the edge of the color space and are on the verge of clipping?  Is the shift related to the rolling off to prevent that?  I think the lower chroma colors will perhaps behave in a more linear fashion, at least until such time as they start to approach the clipping point as well.  If you actually put the Lab data for a few points in a tabular format, it will be relatively easy to see whether the shift is chroma and or the more objectionable hue shift.  Again, that will depend on the color chosen and that has to be taken into account if the data being reviewed is Lab.  Things like saturation/chroma cannot be fully expressed with the Lab equation to the extent of looking at one piece of the measurement, so seeing the three data points would be necessary to accurately interpret the results.  

If you guys would let me know what software you're using I would be happy to assist.  I'll say up front you guys probably know far more about electronic imaging than I do.  I do know color and the various methods of measuring it very well however, so I might be able to assist in that area.  Now I need to go take a closer look at the latest charts you posted, since they came in while I was typing my previous post Smiley

**I should be more clear, when I said a table of the measurements I meant the absolute Lab values as opposed to calculated differences.
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Jim Kasson
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« Reply #35 on: April 20, 2013, 04:29:36 PM »
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I'm not even sure what options for color equations you have in some of the software you are using (I haven't used those personally).  

Matlab is a programming language optimized for manipulating matrices. You can view a color image as a nxmx3 matrix. The good news is: I can implement any color measure I want. The bad news is: I have to program it all myself.


I suspect where you will see the largest shift is in the higher chroma areas that are approaching the edge of the color space and are on the verge of clipping?  Is the shift related to the rolling off to prevent that?  

No, it is not. I deliberately picked not-very-chromatic colors. The grid is L* = 50, a* and b* from -50 to +40 in steps of 9, for an 11x11 grid, or 121 points. That everything is well within the PP RGB gamut is indicated by the Exposure adjustment layer in PS working so well in that color space.

I think the lower chroma colors will perhaps behave in a more linear fashion, at least until such time as they start to approach the clipping point as well.  

The colors that experience the greatest chromatic shift are not the most chromatic, but the ones near a* = 0, b* = -50.


 If you actually put the Lab data for a few points in a tabular format, it will be relatively easy to see whether the shift is chroma and or the more objectionable hue shift.  

Go look at the scatter plots. I think you can get this information from them.

Things like saturation/chroma cannot be fully expressed with the Lab equation to the extent of looking at one piece of the measurement, so seeing the three data points would be necessary to accurately interpret the results.  

Yep, that's the reason for the 3D scatterplots.

I do know color and the various methods of measuring it very well however, so I might be able to assist in that area.  

If you're professionally involved in color science, we may have some mutual friends, although I've been out of the field since 1995. I worked on device-independent color, color management, and color image processing research at the IBM Almaden Research Center for six years, and worked with folks from Kodak, Adobe, Xerox PARC, Apple, and hp.

Jim
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« Reply #36 on: April 20, 2013, 04:35:48 PM »
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Eric, I'm just getting started on this and already I can see that you're right about the Exposure control working differently for raw file and for TIFFs. The amount of Exposure adjustment needed in LR PV2012 for the raw files is the same as the amount of underexposure of those files. With the TIFFs, that much Exposure adjustment results in too-bright images.

Jim
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« Reply #37 on: April 20, 2013, 04:55:07 PM »
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Jim,

We may indeed, although I actually work in plastics (color for plastics) so color science is a large part of what we do from a product design standpoint.  We work with pigments and dyes however, to achieve specific colors in various polymers.  I use to know quite a few people at Datacolor, as well as Macbeth.  I'm sort of beyond the hands on stuff these days however so my contacts are pretty old.


I may be entirely missing the point here, but...  I just ran a quick test I THINK along the same lines of what you guys are doing above.  I took 4 shots of a Colorchecker chart, one exposed correctly, then 3 more underexposed shots (in 1 unit increments).  I imported these into Lr5 Beta since I can see actual Lab coordinates there, and measured all 18 color swatches, as well as the 1 white.  I used the correctly exposed image as a control, then pushed the 3 stop underexposed image by 3 stops (which came out exactly where it should btw).  While I do see some color difference between the two, indicating that Lr is doing a little in the pushing process, they are not nearly as dramatic as what I believe I see in the charts above.  Most of the total DE's are in the ~1.50 range, except for the bright yellow swatch which is ~5 units.  

**I understand part of this is comparing the behavior between Lr and Ps, which is something I didn't do.

This is interesting.

John
« Last Edit: April 20, 2013, 04:57:38 PM by John Cothron » Logged

Jim Kasson
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« Reply #38 on: April 20, 2013, 05:03:56 PM »
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 I just ran a quick test I THINK along the same lines of what you guys are doing above.  I took 4 shots of a Colorchecker chart, one exposed correctly, then 3 more underexposed shots (in 1 unit increments).  I imported these into Lr5 Beta since I can see actual Lab coordinates there, and measured all 18 color swatches, as well as the 1 white.  I used the correctly exposed image as a control, then pushed the 3 stop underexposed image by 3 stops (which came out exactly where it should btw).  While I do see some color difference between the two, indicating that Lr is doing a little in the pushing process, they are not nearly as dramatic as what I believe I see in the charts above.  Most of the total DE's are in the ~1.50 range, except for the bright yellow swatch which is ~5 units.

Sounds like what I'm doing without all the programming. I'm a bit behind you here. I have all the images in Lab in PS, and I'm about to align them.

Jim
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« Reply #39 on: April 20, 2013, 05:05:51 PM »
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We may indeed, although I actually work in plastics (color for plastics) so color science is a large part of what we do from a product design standpoint.  We work with pigments and dyes however, to achieve specific colors in various polymers.  I use to know quite a few people at Datacolor, as well as Macbeth.

I still have my copy of Wyszecki and Styles, although it doesn't get much use these days...

Jim
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