different LAB values for same photo on different computer

Forum|Forum|4 years ago
November 12, 2021
3 replies
556 views

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!

macOS

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TheDigitalDog

Inspiring

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:

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

TheDigitalDog

Inspiring

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/pluralsight"

TheDigitalDog

Inspiring

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/pluralsight"