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different LAB values for same photo on different computer

New Here ,
Nov 12, 2021 Nov 12, 2021

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Hello,

 

i work in a photostudio and i just discovered that Lightroom (10.4) shows a different histogram for the same photo on different computers.

I just took a picture via thethering in Set A, i measured it at a certain point and it says in LAB that L 86. When i import this photo on another computer in Lightroom it says that L is 88. So the photo seems brighter on another computer. Does anybody know how this is possible? I really can't explain..

there were no settings activated while importing.

Would be super nice if anybody could help! 🙂

 

Thanks!

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Adobe Community Professional ,
Nov 12, 2021 Nov 12, 2021

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Is their different preset being used or a different camera profile being used on each computer?

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New Here ,
Nov 12, 2021 Nov 12, 2021

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No, unfortunately exactly the same settings.

quote

Is their different preset being used or a different camera profile being used on each computer?


By @Randy Hufford

 

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Adobe Community Professional ,
Nov 12, 2021 Nov 12, 2021

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We need to inpect the original, ideally a DNG with all edits saved to it, and the rendered image to compare the values. They should be identical. Of course, if one exports the image to anything but Melissa RGB (Histogram and Lab values), the Lab values can differ. 

Author “Color Management for Photographers" & "Photoshop CC Color Management"

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Adobe Community Professional ,
Nov 12, 2021 Nov 12, 2021

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Oh and keep in mind the zoom ratio and pixel averaging: LR/ACR always reads 5-by-5 screen pixels at zoom levels of 100% or less, so it may give different values at different zoom levels. If you fit the entire image into Camera Raws preview, you're sampling an average of a fairly large number of pixels - the exact number depends on both the camera's native resolution and the size you've chosen from the Size menu in the Workflow controls. At zoom levels greater than 100%, the sample size is always 5x5 image pixels.

Author “Color Management for Photographers" & "Photoshop CC Color Management"

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New Here ,
Nov 12, 2021 Nov 12, 2021

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Thanks for your reply! 

I took the photo in RAW, so CR2 + xmp and i didn't render it. I just imported the CR2 + xmp in Lightroom on another Computer and the LAB values were different. 

I measured it at a zoom ratio of 100 %. 

I know that it should be identical, that's why I'm so confused..

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Adobe Community Professional ,
Nov 12, 2021 Nov 12, 2021

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You have to render it to measure the Lab values rendered. 

Again, unlike Photoshop where you can place an exact sample with an exact set of sampling (5x5 or otherwise), it's very difficult to get an exact set of 25 pixel samplings in LR unless you try on a large and very solid color. 

Author “Color Management for Photographers" & "Photoshop CC Color Management"

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New Here ,
Nov 12, 2021 Nov 12, 2021

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But shouldn't the photo look identical on both computers even without rendering? I don't get it why it looks "good" on the computer i shoot on and too bright on another computer. I'm sorry, I know ist's difficult to identify the problem without the picture itself. Thanks for your help!

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Adobe Community Professional ,
Nov 12, 2021 Nov 12, 2021

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@EllKem wrote:

But shouldn't the photo look identical on both computers even without rendering? 


ONLY if both displays are identically calibrated and profiled for a match. 

Author “Color Management for Photographers" & "Photoshop CC Color Management"

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New Here ,
Nov 12, 2021 Nov 12, 2021

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Oh okay, i was wondering if it has to do something with the monitor but I thought it doesn't matter because the data of the file is measured and should be identical. Okay maybe this is the problem, i will have a look on monday. I really appreciate your help, thanks a lot! 🙂

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Adobe Community Professional ,
Nov 12, 2021 Nov 12, 2021

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You can see, in Photoshop and LR (two captures) how a few values change due to location of the cursor and how 25 pixels are averaged. What you report is to be expected even when the images are rendered into the same color space (Lab shouldn't care), but again, in LR, you are viewing 25 pixels for the average and it is shown differently (decimal points) from PS. It also doesn't truncate values like Photoshop does (+/- 127/8)

 

All done below at 100% zoom and 5x5 sampling in both hovering over blue label:

 

LR sampling 1LR sampling 1LR sampling 2 (slightly different)LR sampling 2 (slightly different)PhotoshopPhotoshop

Author “Color Management for Photographers" & "Photoshop CC Color Management"

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