Color Management Overview
This page provides an overview of color management for digital photography. Color management is the method for specifying and preserving color in a digital image.
Color management basics
Color profiles help preserve color at every step
How does the profile get there?
What do I do if there's no profile?
How do I know what profile is attached to the image?
What profile is my raw file?
How do I set up Photoshop so the profile is used properly?
What is bit depth?
Which color space should I use?
Creating a monitor profile
Creating a printer profile
Creating a camera profile
Color management and CMYK printing
A conventional digital color photo uses a mix of red, green and blue to create the colors in an image. But the RGB values for a pixel don’t define an exact color unless they are accompanied by a color profile. This color profile lets the computer know how to decode the color properly. If you don’t tag an image with profile information, then Photoshop (or any other program) will not know how to interpret the color, and will just have to guess what the RGB numbers mean. Given the number of different color profiles in existence, it’s likely that the program will guess wrong. Figure 1 shows how the same RGB numbers produce different colors depending on which profile interprets the values.
Figure 1 When is a color not just one color? When it does not have a color profile. This is an illustration of how RGB numbers describe different colors depending on the color space that’s used. Each of these colors has the same RGB value, but each color space represents that RGB value as a different color, because it uses a different method to describe color.
Figure 2 How do you preserve a color? When a file has an embedded profile, it is easy to preserve its color by converting to the new color space using the color numbers of the embedded profile. This is an illustration of how the RGB numbers need to change to describe the same color in a new color space.
In order to get the color right on the computer, there has to be a color information “chain of custody” that goes something like this:
- The file must have an indication of what color space was used when it was created or last edited—a color profile that is embedded in the file.
- A program that opens the file needs to know how to use the color profile to properly interpret the colors for each pixel.
- When an image is sent to a monitor or a printer, the computer uses a specific color profile to help compensate for the color signature of the device. So, for example, if your monitor or printer makes shadows too blue, this profile can take some blue out of the darks.
Profiles are created and attached to files in a number of ways:
- When a JPEG file is created in a digital camera, a profile is usually attached to it. Many cameras give you a choice between sRGB and Adobe RGB.
- When a raw file is created in a digital camera, it has no inherent profile. The profile gets applied to the raw file as it is opened by a raw converter into a rendered filetype, such as TIFF, JPEG or PSD.
- Scanners have the option of attaching a profile when the image is scanned. Do so.
- If you create a brand new file in Photoshop, it will be created in the working space that is specified in the Photoshop Color Settings, shown below. Make sure the Embed Profile checkbox is selected in the Save dialog.
- When a file with no embedded profile is opened in Photoshop, you should determine the "best" profile to use then embed that profile when you close the file.
|Figure 3 When you save a file in Photoshop, you should always embed the profile so the next time a program opens it, the color can be rendered correctly.|
If an image has no profile, and you have Photoshop set up correctly, you should get a warning that looks like that in Figure 4.
Figure 4 If an image does not have a profile, you should assign one when it gets opened in Photoshop. Open the file, with a profile – sRGB is a good guess. If it does not look right, then try other profiles until you find the best match.
- You can assign various profiles, and see the effect on the image.
- You should NOT choose "Don't Color Manage". That command should really be named "Color Manage Incorrectly".
- Make sure you embed the profile when you save this file so that it will be color managed in the future.
An easy way to determine the profile of an image is to open it in Photoshop and view the information at the bottom left of the Photoshop window as shown in Figure 5. If an image doesn’t have an embedded profile, this will report that the image is untagged.
Figure 5 The readout at the bottom of the Photoshop window shows you several kinds of information, including the color profile. If it's not showing, click the triangle flyout menu then choose Show>Document Profile.
Trick question! Camera raw files don't have a profile in the conventional sense. While the sensor in a digital camera has a color "signature", it does not have a conventional color profile. Raw files contain scene-referred color information (described in Karl Lang's excellent white paper), which is fundamentally different to that of a rendered file such as a TIFF, JPEG or PSD file. A raw file only gets a profile once it's been opened and exported as a rendered file. The color space setting on the back of your camera (usually a choice between Adobe RGB or sRGB) is used to create JPEGs made by the camera.
Read more about assigning profiles to raw files in this section
Figure 6 shows a screenshot of the color settings in Photoshop that we suggest.
Figure 6 Here's a screenshot of the short version of color settings in Photoshop. The most critical parts of this dialog are the checkboxes that prompt you to take some action when profiles are missing or mismatched.
Bit depth is the number of steps between white and black in a color channel.
- In a grayscale file, this is used to describe the brightness of a pixel. An 8-bit file has 256 steps between color and black and white. A 16-bit file has 65,536 steps between white and black.
- In a color file, each color channel – red, green and blue, for an RGB file – has 256 steps between brightest and darkest tones for 8-bit and 65,536 for a 16-bit file.
- A 32-bit file has 4,294,967,295 steps between brightest and darkest tones. These are generally referred to as high-dynamic-range (HDR) images.
Choosing a color space depends on what you’re doing. Photoshop gives you several choices to use as a working space. In general, you should be working in one of the wider gamut spaces, such as Adobe RGB (1998) or ProPhoto RGB, if you are creating masterfiles. You will likely need to convert to a smaller color space, or even to a CMYK color space, when creating delivery files or output files.
This page has an in-depth discussion of how to evaluate and use the appropriate working space. For those of you who don't like to read, here's the executive summary.
- If you are editing in Photoshop, both Adobe RGB or ProPhoto RGB are good choices. ProPhoto RGB should only be used for 16-bit images.
- If you output to the web, send to minilab for printing, or are sending files to someone who does not implement color management, you should use sRGB on output.
- If you are sending files for reproduction, use the profile that is specified by the recipient. If none is specified, sRGB is probably the safest choice.
- If you are sending CMYK files out for reproduction, you should use a color space specified by your printer, or, if no space is specified, send in GRACoL for sheetfed presses, or SWOP for grade 3 (brighter white) or grade 5 (less white) papers for web presses.
The only way to know that your monitor is reproducing the image to the best of its ability is to calibrate and profile it. You need to use a hardware calibration device to measure the color of the monitor and create a profile that works for that particular unit. Lots more information here:
Read more about Monitor Calibration and Profiling in this section
Your desktop printer comes with some profiles that may be very accurate. If you want the most accurate printing your machine is capable of, you need to create a custom profile for that particular printer. We show you how here:
Read More about Desktop Printer Profiling in this section
It's even possible to create a profile for your particular digital camera that gets applied to the images when they are converted from raw to rendered. Here's how:
Read more about Camera Profiling in this section
If you are sending images off for printing, you may be asked to create the CMYK conversion. Since the color model for CMYK is so different to RGB, you need to add a few options into the process. We take a look at that workflow here:
Read more about Commercial Printing in this section