Lightroom RGB Percentage vs Photoshop RGB numbers

Trying to get my Lightroom refined images as close as possible to Photoshop optimized versions, I discovered that the Lightroom RGB percentages do not match Photoshop RGB numbers.

Lately I have been finishing my underwater images in Photoshop, as Lightroom does not offer the amount of color correction control I waned.

However, reimporting my corrected images into Lightroom, the black point RGB numbers were not  consistent with my Photoshop RGB numbers.

My normal workflow is:-

  1. Import my RAW underwater images into Lightroom and optimize them as far as possible.
  2. Open the image into Photoshop with the Lightroom adjustments.
  3. Do a final colour correction in Photoshop using a Curves Adjustment layer and  RGB numbers. Using “Color Correction by the numbers” tends to give the image more punch, with blacks set to 12:12:12 (5%  black) and whites to 243:243:243 (5% white). (This technique is explained in detail in Photoshop CS4 – Color Correction by Taz Telly on Lynda.com.)
  4. Save the Photoshop modified image with layer modifications in TIF format.
  5. Import the modified TIF file back into Lightroom.
  6. Knowing the final RGB numbers in the modified TIF file, do a final adjustment to the original RAW file in Lightroom, to get the RAW and TIF images as close as possible.

When I set my blacks and whites to 5% in Photoshop and imported the images back into Lightroom, I noticed the blacks were not 5% black.

I was stumped on this for a while until I did a bit of experimenting to figure out what was going on.

RGB1998-test-patternFigure 1 – RGB1998 Test pattern.

Creating the test pattern in Figure 1 using a RGB1998 colour profile, the RGB 12:12:12 (5% black) in Photoshop measured 2.2% black in Lightroom.

Likewise the RGB 243:243:243 (5% white) in Photoshop measured 4.6% white in Lightroom.

What is Happening?

To fit in as many colors as possible, Lightroom uses the Melissa RGB color space (named after one of the Lightroom team members), which approximates the ProPhoto RGB profile, and is larger than the RGB1998 and sRGB profiles.

When my Lightroom image is exported to Photoshop, the image is converted to my RGB1998 working color space, which alters the black point.

This means:

  1. If I have an image in Lightroom that I want to adjust for 5% black in the working RGB1998 color space, I need to set the black points in lightroom to 2.2%.
  2. If I have an image in Lightroom that I want to adjust for 5% white in the working RGB1998 color space, I can use the Lightroom setting as 95.4% is close enough to what I want.

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