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Author Topic: Before-after comparison: problem?  (Read 2446 times)

bns

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Before-after comparison: problem?
« on: June 03, 2018, 04:47:02 AM »

For some time I have a problem with the before-after comparison in the development module of Lightroom. My suspicion of something “funny” going on dates back quite some time, way before LR Classic I think.
Lately, working on images with a lot of dark tones, I got worried.
I use the before-after comparison – either the sequential comparison using the “\” key or the side by side “Y” key - a lot when making the last subtle adjustments to an image.
I turns out that using the before-after comparison between two identical development states, the comparison shows a difference. I have tried to make this visible with the attached figure.
Left is “before”, i.e. the original image, right is “after”, that is after pushing the development reset button. The dark tones in the before image are noticeably lighter than in the after image. The tones in the after image seem to be the same as in the original.
I suspect that something similar goes on in the softproof mode.

Has anyone seen this kind of effect? What is wrong with me or with my system? Any ideas?

Configuration: LR Classic 7.3.1., Windows 10, display Eizo CX271 calibrated with i1Display Pro, set at 5500K, 80 cd and white-black ratio 250:1.

Cheers,
Boudewijn Swanenburg
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Mark D Segal

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Re: Before-after comparison: problem?
« Reply #1 on: June 03, 2018, 08:22:45 AM »

To my eyes the right image is very, very slightly more saturated/darker than the left image, but one needs to look long and hard to perceive any meaningful difference, so the problem is unclear (to me from my well-profiled NEC PA271 monitor) from this presentation.
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Mark D Segal (formerly MarkDS)
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bns

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Re: Before-after comparison: problem?
« Reply #2 on: June 03, 2018, 11:32:42 AM »

Hi Mark, thanks for your reaction.

I have imported the screen shot displayed above again into Lightroom. Then I read the Lab values of the discrete greyscale steps at the bottom of the image.
The values below the block labled 24 (the brightest of the dark blocks) reads 14.7 0.0 0.0 in the left (before) image and about 11.8 0.0 0.0 in the right (after) image.
To me that is a significant difference, where zero difference is expected.

Boudewijn Swanenburg
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Mark D Segal

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Re: Before-after comparison: problem?
« Reply #3 on: June 03, 2018, 03:06:22 PM »

OK, the difference is there if you measured it. I can't explain it. When you push Reset does EVERYTHING go back to exactly the way it is portrayed in the "before" state? If it does, there should be no difference, but perhaps something that was adjusted doesn't reset?
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Mark D Segal (formerly MarkDS)
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bns

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Re: Before-after comparison: problem?
« Reply #4 on: June 03, 2018, 03:37:26 PM »

Yes, the two versions are absolutely identical. I verified that by measuring the pixel values of the before and after images in single view.
I would very much appreciate if you could try to duplicate my observation on your system with one of your images.
At low tonal values the effect is most pronounced.
If the effect is real, it looks like to be a Lightroom bug. If it cannot be reproduced, my system must have a problem.
By the way, I see the same effect on a non calibrated laptop.

thanks,
Boudewijn Swanenburg
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Mark D Segal

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Re: Before-after comparison: problem?
« Reply #5 on: June 03, 2018, 03:44:31 PM »

I'm using Lr 7.1 using Mac OSX 10.11.6, so I'm not sure anything I test would be determinative. Whatever I find leaves open various possibilities with the one exception being that if I can replicate the problem we can say it's an application issue. If I have anything in Lr that is useful for such a test I'll do it. Need to check.
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Mark D Segal (formerly MarkDS)
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Mark D Segal

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Re: Before-after comparison: problem?
« Reply #6 on: June 03, 2018, 04:03:16 PM »

OK, I have the same Outback printer test photo in my Lr catalog so I pulled it up, made a huge Exposure adjustment, then clicked Reset, then pressed Y for the Before and After view and measured all the dark patches from 2 to 24 in the grayscale ramp containing the two ends of the scale (very dark and very bright patches) in the Black surround. In both the Before Image and the After image all readings are identical for the same patch. The Before state = the After state in each image and the same patch # has the same value in both the Before and After image versions. So I see nothing wrong with Lr 7.1 in OSX 10.11.6.
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Mark D Segal (formerly MarkDS)
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bns

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Re: Before-after comparison: problem?
« Reply #7 on: June 03, 2018, 04:09:39 PM »

Yes, in the individual images the values are identical. But if you viually compare the before and after image ("\" key works best) don't you see a difference? The before patches beeing lighter?
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Mark D Segal

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Re: Before-after comparison: problem?
« Reply #8 on: June 03, 2018, 04:23:38 PM »

I did that - I compared the Before and After images with both on the display so I could readily pass the eyedropper back and forth between the one and the other, and as I said, for the same patch the value is identical for the two states. I think this is conclusive that at least here there is no issue to report.
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Mark D Segal (formerly MarkDS)
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bns

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Re: Before-after comparison: problem?
« Reply #9 on: June 03, 2018, 04:32:16 PM »

Hi Mark, thanks for your effort.
At my side I get the same result with the Eyedropper. But vsually I see a difference.
Could you possibly make a screenshot of the before-after comparison with the "Y" key, and measure the pixel valus form that?
That is where I got the difference.

Boudewijn Swanenburg
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Mark D Segal

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Re: Before-after comparison: problem?
« Reply #10 on: June 03, 2018, 04:44:28 PM »

You are welcome.

I don't consider it reliable to take measurements from screen shots which have been manipulated from the original state of the images themselves. Reading directly off the Lr representation of the raw file is the only scientific way to do this and if the numbers are the same the visual impression should be the same; I don't understand why in your case you see a difference. Is it possible that your monitor illumination is uneven? Anyhow, here is a screen-grab of what I see. 
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Mark D Segal (formerly MarkDS)
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Wayne Fox

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Re: Before-after comparison: problem?
« Reply #11 on: June 03, 2018, 06:25:06 PM »

Just thought I would mention that you don't actually "know" the current "before" state that is used unless you explicitly set that state, or remember when it was set.  The before state can be any step in the history, and LR does seem to have an unusual behavior on what it does to the default before when you do things like reset the image.  To make sure the before state is what you believe it is is to right click on it and set that step to the before.

This may not be relevant, rushing to an appt so sry I don't have time to read the OP in detail right now to understand the full problem in that post, but on the off chance it might be pertinent I thought I would throw this out there (and also sry if this was mentioned in a follow up post).
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bns

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Re: Before-after comparison: problem?
« Reply #12 on: June 04, 2018, 05:07:48 AM »

Hi Wayne,
Thanks for coming into the discussion. Yes indeed, you have to define  the before state by right clicking on it. That is one of the nice things about the comparison feature. One can compare the current state, with any of the previous states
What I did, was comparing the state after Reset, with the state after Reset again i.e. two absolutely identical images.

@ Mark
Thanks a lot for presenting your screenshot. I downloaded it, imported in LR and used the eyedropper to investigate the pixel values. I agree that pixel values from screenshots may not be the most accurate in absolute terms, but for a relative measurement it may be OK.

The L values I get from your image are:
Block 8: left 12.3 and right 14.0
Block 16: left 5.7 and right 9.2
Block 24: left 3.0 and right 5.1

I am almost sure that if you would toggle between the before and after image with the “\” key, you will visually confirm that there is a difference between the two.

I repeated my previous analysis on a cropped version of the same image. The result is attached. "Before" is up, "After" is bottom.
This makes the difference more easily visible.

While fine-tuning the appearance of (deep) shadows in an image, I find this effect very disturbing and I would very much like to pinpoint the cause.

Boudewijn Swanenburg
« Last Edit: June 04, 2018, 05:13:17 AM by bns »
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Mark D Segal

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Re: Before-after comparison: problem?
« Reply #13 on: June 04, 2018, 09:16:20 AM »

You're right. Doing it by using the "\" key produces different values in the deep quarter tones. I can also confirm this happens whether or not one has edited and then reset the image. So there is something going on here between the two states ("Before" loaded/not loaded) that needs to be explained. It's either an application bug going back some time or there is some deep dark reason I, at least, am unaware of. Thanks for your persistence on this one! It should be reported to Adobe for follow-up.
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Mark D Segal (formerly MarkDS)
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bns

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Re: Before-after comparison: problem?
« Reply #14 on: June 04, 2018, 10:02:47 AM »

Thanks, Mark.

The "funny" thing is, that in the adjacent before-after display, using the eye dropper, one reads the same values, but the brightness is different. It looks like the before and after versions are using different lookup tables (or transformations) between data and display.

As I have no experience with contacting Adobe, could you possibly suggest a way to bring this problem to their attention?

cheers,
Boudewijn Swanenburg
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Mark D Segal

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Re: Before-after comparison: problem?
« Reply #15 on: June 04, 2018, 01:07:25 PM »

Hi Bouewijn,

Adobe has a Lightroom site for reporting problems, here: [type]=problem]Lightroom-Problems

That said, I have no idea how effective it is. But worth a try.
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Mark D Segal (formerly MarkDS)
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john beardsworth

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Re: Before-after comparison: problem?
« Reply #16 on: June 04, 2018, 01:17:39 PM »

I wonder if it relates to the previews generated either upon import or otherwise before going into Develop.

Tim Lookingbill

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Re: Before-after comparison: problem?
« Reply #17 on: June 04, 2018, 05:04:51 PM »

Thanks, Mark.

The "funny" thing is, that in the adjacent before-after display, using the eye dropper, one reads the same values, but the brightness is different. It looks like the before and after versions are using different lookup tables (or transformations) between data and display.

cheers,
Boudewijn Swanenburg

Just speculating but does this happen at 100% zoom views or smaller?

I know in Bridge CS5 the main preview and thumbnails render in sRGB (which is encoded in that non-standard oddly shaped gamma curve that resembles the behavior of that gray ramp). I can hunt these truncated previews in my OS's Bridge directory and get info indicates they're tagged in sRGB.

I don't do any Auto/Reset process to check if shadows are affected similar to your situation. I've never had this problem in LR4 except I have to have a matrix color space like ProPhotoRGB set in Soft Proof or else black and shadows look a bit milky in Develop module compared to how the same file looks in Photoshop where there is no milky shadows.

It may be that at certain zoom levels the sRGB preview takes over and doing anything Auto to it references it's non-standard gamma curve space.
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bns

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Re: Before-after comparison: problem?
« Reply #18 on: June 05, 2018, 03:57:56 AM »

@ John
Thanks for the suggestion.
I now compared two states with all kinds of edits in between. At one point I make a snapshot. Then I apply various edits. Recall the snapshot and compare. Exactly same effect, most noticeable in the dark tones.

@ Tim
Good suggestion. But no. I tried 100% view and may other zoom levels. Same effect.
Different rendering of separate previews could certainly be a cause of the effect. Don't know how to verify.

@Mark
Thanks. I'll try to wake up Adobe.
I also did send a PB to Jeff Schewe.
« Last Edit: June 05, 2018, 04:06:18 AM by bns »
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Wayne Fox

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Re: Before-after comparison: problem?
« Reply #19 on: June 06, 2018, 12:05:13 AM »

One thought, if you are comparing an image that has been reset, reset doesn't actually reset the image to how it was when it was imported, it resets the image as though you are importing it again.  So if anything has changed from the time you  first imported the image (such as the newer version of LR that might be using different profiles) there might be a difference.  An example I ran into recently, if you change a camera default to apply some modified settings (such as a different profile) , all you have to do to apply that new default to images already imported is to reset them.

Random thought.  I just imported a series of images, made some changes to a few, reset them, and then compared, and I'm seeing identical before afters. 
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