COLOR MANAGEMENT FOR DIGITAL CAMERA USERS

by Hugh Stockton

This discussion is limited to managing color from camera capture through PhotoShop to Screen Display, Printer, and file. I make several assumptions:

1. You shoot RAW
2. You use PhotoShop
3. You want others to see what you see

Some background

1. Your camera captures a wider range of colors than you can see. The profile associated with the camera determines the colors available to be processed.
   
   
2. Your camera captures a wider range of colors than your monitor can display. The profile associated with the monitor determines what colors presented to it are actually displayed.
   
   
3. Your camera captures a wider range of colors than your printer can print. The profile associated with the printer determines which of the colors presented to it will be printed.
   
   

Some definitions

1. Standard Color Numbers - ICC Profile - a set of color values produced by the ICC (an international organization that does that sort of thing) generally accepted to be what is seen by persons of average vision in normal viewing conditions
   
   
2. Color Equivalent Numbers - the device specific values produced by input devices (cameras/scanners) in the capture process, or the device specific values required by output devices (monitors/printers) in order to produce visual color
   
   
3. Profile - a software/firmware translator that converts device specific color equivalent numbers to standard color numbers or standard color numbers to device specific color equivalent numbers.
   
   
4. Color Space - a specific set of standard color numbers such as:
   
   
   • ProColor RGB - a color space coming into use for managing printer workflow - contains more colors than Adobe RGB
   • Adobe RGB - the color space commonly used to manage printer workflow - contains more colors than sRGB
   • sRGB - a narrower color space - fewer colors - generally accepted as the limiting case for internet use and for applications that don't manage color, i.e. Internet Explorer
     
     
5. Gamut - the set of all colors/color numbers usable by a specific device
   
   
6. Intent - how a color managed application/device deals with out of gamut colors values
   
   
7. Conversion Engine - the software routines that actually do profile conversion and intent manipulation
   
   
8. Perception - the Intent that set the black points of two color spaces to the same value, then makes the result color space relative to the source color space - generally accepted as most often producing the best results
   
   
9. Relative Colorimetric - the Intent that sets out of gamut colors to the closest available in gamut ones - next most commonly used
   
   
10. Saturation and Absolute Colorimetric - other intents - not commonly used
    
    

How Your Camera Handles Color

The camera sensor does NOT capture color. It captures the intensity of the light passed through by the lens and focused on each pixel. There is a pattern of colored filters on the sensor such that a given pixel only sees light through a single colored filter: either red, or green, or blue. The RAW file produced by the camera contains a list of values of the amount of light 'seen' by each pixel. These are camera specific values. The RAW file translator, PhotoShop Browser, Capture 1, or whatever you use, reads one value at a time. By the position of the value in the file it knows which color filter was used. If the pixel being read was a "Red" pixel, that value is assigned to red. The software also knows which surrounding pixels captured green and blue information and uses them to assign a green and blue value to the current pixels being read. With these three values a color equivalent number can be calculated.

Each camera requires a 'profile' that can be used to translate the color equivalent numbers into 'standard' numbers that can be provided to and understood by other devices. The translated numbers exist in a working space. Each output device requires its own profile to translate from the working space to color equivalent numbers it can use.

So, color in the real world is captured as light intensity by the camera, made color values by the RAW translator, normalized by the camera profile then:

1. passed to the monitor, converted to monitor specific color equivalent values by the monitor profile, and used to drive the display
   
   
2. passed to the printer, converted to printer specific color equivalent values by the printer profile, and used to drive the printer
   
   
3. written to a file
   
   

How I Manage Color

What does that mean to you? I don't know, but I can tell you how I do it and hope that, and the previous discussion, allow you to decide what's best for you.

First, I set PS CS to ProPhoto so the maximum range of color information is available. Then I set the PS Working Space to sRGB for web processing, or ProPhoto for print processing. I've calibrated and produced profiles for my monitors using the Pantone Spyder.

After processing for the web and just before "Save For Web" I convert the image profile to sRGB. Note that if you use "Two Up" in Save For Web, and set the display to "Use Document Profile", you will see, on the left, how unmanaged applications will likely show your image.

For printing, I just select "Printer Color Management" and, in the printer set up, "Auto" and let the Epson 1280 do its thing. So far, I'm very pleased with the results. I've found that differences in paper seem to make more difference than profile management for printing. I'm sure many will disagree with that. Note that for larger prints and/or commercial work, I use a professional printer.