What do the Numbers Mean in Post Processing


Tree in rocks image

know the numbers and you will know your image

Ever ask yourself what do the numbers mean when post Processing in, Adobe Camera Raw, Photoshop or Lightroom? If you haven’t you should as they are very helpful at letting you know how your final image will reproduce or look to the viewer. There are a few important things the numbers tell us among them are the white and black points where detail is lost and how neutral or color balanced your image is. Just to complicate things a little Lightroom uses a scale of 0 to 100 while the RGB space in Adobe Camera Raw and Photoshop use 0 to 255. If you are going to print the numbers in the CYMK color space uses 0 to 255 but do to the print inks not being equal the color balance, white and black points are totally different than any other space. I will write at a later date more complete information on color balance in the CYMK space.

I have done post processing under some terribly poor conditions doing prepress work. Bad lighting, bad monitor and no way to proof my work but all was fine in the end because the numbers never lied. One time I had a dark, and I mean dark green chair that printed neutral black. Well it turned out the printer thought that I let the yellow go a little two high so he color corrected the image. Yellow might get you confused if you don’t know the CYMK color space but when yellow a very strong color goes up the blacks go green.

The endpoints of an image are the points where detail is lost in the blacks and the whites. Most indicators in our programs show the limits of the color space which is way past where detail is lost.

Below is a chart showing the 95%, 50%, 10% and 5% points and a 100% and 0% reference bar. The 95% point is where detail is lost in any higher value. The 50% point is for your reference and the 5% point is the point of last detail any darker you will have no detail. Next the 10% point will look lighter on a screen as it is backlit and in real life if the image is printed this is a better selection as your black point. The misunderstanding of this fact is one of the reasons prints seem to be darker than on your screen. Your printer works from the numbers and the numbers don’t lie. If your print is too dark increase the contrast in the dark area and raise the values.

What the numbers mean

What the numbers mean

This chart was put together in Photoshop using the Pro Photo profile and converted to sRGB for screen display. The numbers in the sRGB file are slightly different as Pro Photo profile is much larger and so things a squeezed a little to fit into the smaller sRGB space. How this chance occurs is controlled by the rendering intent of your color setup. I use relative colorimetric which is best for prepress and works very good in other situations. The Perceptual rendering intent is also workable and I do softproof using both but most the time choose Relative Colorimetric. The numbers in lightroom will differ and the numbering scale is not linear. So after completing the above file I measured the Lightroom numbers to be the same as the file converted to sRGB even though my Lightroom is set up for Pro Photo.

Lightroom is very visual in the way it works and it seems to display things as they will appear on a screen in sRGB so it is important to know the numbers. The end point for White is 96.2 and 5% Black is 5.9 with printable detail 10% black is13%. Middle grey is 57.4 percent. These numbers are the same for sRGB files and should be the numbers used in Lightroom even though you work in another color space inside lightroom. This is not bad because most screens are built to cover the sRGB space so you are working with the numbers that work for a vast amount of people.

I am hoping this blog works well for you and welcome any feedback or questions. Do not forget to subscribe so you wont miss the next blog. Until next time “Keep on Shooting”.

About John Aydelotte

I aspire to pass on some of the 40 years of imaging knowledge I have acquired. I have a true passion for imaging and wish to enjoy my retirement from Commercial Photography by creating images from my heart. I am still taking a few Freelance jobs but would love to teach and lead others on their amazing photography journey. I have two grown children and 7 grandchildren. I am focusing on photography, education and retirement.


What do the Numbers Mean in Post Processing — 3 Comments

  1. John,

    I think you need to add a little information to this.

    The RGB you mentioned in Photoshop is 8-bit RGB. This one has 256 levels of grey. But eg. when TV went to 10-bit, we had to recalculate, as 10-bit gives us 1024 levels of grey. And in Photoshop, you can work in 16-bit as well. This gives you 65,536 levels of grey.

    Lightroom, on the other hand, works in 32-bit float. This gives you a virtually unlimited number of grey levels. And you can not change the bitlevel in Lightroom. But you can convert (export) to whatever format and bitlevel you want. As far as I know, going to TIFF, 16-bit and ProPhoto RGB color space. As far as I have been able to determine, this gives the best possible chance to keep the original quality. My idea is to keep the high quality as far as possible, and not reduce anything until you really have to.

    So comparing 8-bit RGB numbers in Photoshop to 32-bit float in Lightroom will at best be academic. I have not been able to determine what the 0-100 scale in Lightroom represent – maybe percent? It is, however, interesting to know the relationship between what we see on the screen and what comes out on a print. You seem to have a firm grasp on this, and I would love to know more! As my background is screen based (TV, film and computer), I need to read up more on CMYK, printing and inkjets. I want to make prints of my images 🙂

      • Svein Thanks for your comment. I do work in 16 bit in photoshop but you find it interesting that photoshop is really only 15 bit and the extra bit is used by photoshop. The numbers displayed in photoshop are 8 bit numbers representing the chosen RGB profile when you go from Prophoto to sRGB the numbers will change to fit the space you are working in. Lightroom as you said works in 32 bit but the numbers it displays are percent but the interesting thing is the numbers are the same as a prophoto file converted to sRGB. I would suspect that lightroom displays a sRGB color space as a lot of monitors will only cover the sRGB gamut. I did the process a few times and alway got the same answer. This is a good way to work as it show you only what you can see. The last white in Lightroom 96.2%, middle grey 57.4%, 10% black for printing with detail 13% and 5% for detail on the screen 5.9.