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4 Messages

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102 Points

Wed, Jan 3, 2018 10:04 PM

Photoshop/Lightroom: Is there a way to match Color Sampler Tool behavior between applications?

I have a few questions on the Color Sampler Tool in Photoshop and in Lightroom.
In Photoshop we can measure the lab values of a single pixel up to an area 101x101px. When we measure an area, what is the algorithm of the averaging of the lab values of the pixels included?
Also, in Lightroom the measurement is always in area 5x5 pixels of the screen monitor if I'm not mistaken. Is there a way to use Color Sampler Tool exactly the same way as in Photoshop?

I've measured differenced in measurements in 8 and 16bit Tiff files from the same raw file. Is that expected?

Responses

5 Messages

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200 Points

3 years ago

Color samplers used a zoom-independent sampling such you can zoom in and out and the values should not change. But WB is zoom level dependent. So if you want to average over a larger area, zoom out. 

4 Messages

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102 Points

3 years ago

Andrew thank you for your time to answer!
Since the color sample can measure an area that contains more than 1 pixel, the the different lab values get averaged out to an overall measurement. I'm looking for the averaging algorithm for start..

Champion

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1.4K Messages

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24.5K Points

3 years ago

Just a guess but I am betting that Adobe won't share the algorithm used.  

4 Messages

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102 Points

3 years ago

Hello Rikk, i've contacted Adobe Help-Desk and they ask me to contact the Color Sampler developer team here, but i'm not sure if they'll notice my post. The algorithm is just a part of what i'm looking for. Actually, having the same tool in Lightroom and Photoshop would matter more.

Champion

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2.2K Messages

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37.4K Points

3 years ago

Since the color sample can measure an area that contains more than 1 pixel, the the different lab values get averaged out to an overall measurement. I'm looking for the averaging algorithm for start..
My guess is that the pixel RGB values are added, divided by the number of pixels sampled, and then converted to Lab values.

But WB is zoom level dependent. So if you want to average over a larger area, zoom out.
The Lightroom WB Eyedropper uses a sample area of 5x5 to 17x17 pixels as set by the 'Scale' slider. This is independent of the Zoom View setting and always samples a fixed area of 5x5 to 17x17. However there are some caveats.  The Eyedropper tool panel displays the average RGB value of the sample area pixels, but only as percentage value (0-100%). The Histogram also displays the average values in RGB percentage, but can also be set to display Lab values (right-click in Histogram). Unfortunately with the current implementation the sample area used for the Histogram readings is "fixed" at 5x5 pixels regardless of the Scale setting used. See this post for more information:

https://console.getsatisfaction.com/photoshop_family/conversations/lightroom-white-balance-eyedroppe...

4 Messages

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102 Points

Todd thank you very much for your reply
What you describe about the 5x5 pixels is one of the major issues i have with the Color Sampler in Lightroom. Although i still consider it a superior option to the Color Sampler Tool in MacOSX.


Thank you for your time.

ps: I'm having trouble opening the link for some reason