Qimage - Color Management Information

Qimage now offers color management for your monitor and printer through standard ICC/ICM profiles.

Why do we need ICC/ICM profiles?

If you are not familiar with ICC/ICM profiles and "color spaces", you might think that specifying a red, green and blue value is enough information to specify the hue, saturation and brightness of any color. Sounds simple enough doesn't it? The 24 bit images from your digicam can specify an amount (brightness) of red, green and blue for every pixel, so why do you need more than that? You may have learned in school about the fact that almost any color in the spectrum can be produced by mixing a certain amount of red, green and blue light. Most likely, nobody told you that how much red, green and blue you need to represent a color depends on how you define red, green and blue, i.e. what frequency you consider to be pure red, pure green and pure blue. The truth is, you can never quite cover the entire spectrum using only three primaries. You can always get close, but the range of coverage is never perfect.

Monitors and printers are designed with the above in mind. Monitor manufacturers, for example, will tweak the performance of a monitor by changing the characteristics of the phosphor (red, green and blue elements) in the tube. They do this to give you the greatest coverage of the color spectrum within the limits of the device. A cheaper monitor with less range will generally use slightly difference frequencies for red, green and blue than a more expensive model. Printers have an analogous problem with ink colors and the yellow, magenta and cyan primary colors. Herein lies the problem. To get truly accurate color on devices that define their color differently, you need ICC/ICM profiles that describe the characteristics of how an image or device reproduces color using primaries. You can think of an ICC/ICM profile as a way of describing exactly how the primary colors map to device independent color, i.e. a method for describing exactly what "color" you get when mixing the primaries.

How big is the problem?

Fortunately, there is a standard color space in use today that serves as a profile for the "standard" desktop monitor. This color space, called sRGB, is the color space used for all consumer/prosumer digicams and most "non-professional" workstation monitors, and represents most of what you see on the web. Most newer model monitors will reproduce accurate color right out of the box if you simply display an sRGB image on the device without worrying about color space. This is probably why most who read this article might be wondering why they need something new because they have never noticed any problem with their images. If you have a relatively new monitor and printer and always view and print images that are stored in their (default) sRGB color space, the advantage of using ICC/ICM profiles may be small and the associated improvement to your images subtle in some cases. In others, however, the difference can be quite noticable even when using the latest technology. It all depends on the manufacturer and how well they think they need to match color to sell you a product, but more on that later.

Is profiling worth the effort?

For 80% to 90% of the consumers reading this article, the obvious question might be: why bother? Aren't the results we get without using profiles good enough? That's what the manufacturers of your camera, monitor and printer are betting on. The methods that manufacturers use for producing just about any device include a cost/benefit analysis that maximizes profit based on the minimum requirements needed to meet the majority of consumer's needs. However, as digicam image quality and resolution continue to increase, consumers are developing a more discerning eye for image and color quality. Judging by the response to some of our Qimage plugins, more people may appreciate the ability to reproduce truly accurate color than some manufacturers realize.

Monitors are usually better than printers, in that they can usually deliver close-to-accurate color right out of the box, at least if you "stick to" the sRGB color space. In addition, many monitor manufacturers are now supplying accurate profiles in the "Downloads" area of the "Support" section on their web site. Printers are a bit more difficult because a different profile is needed for different types of ink and different types of media (paper). It would be an additional cost to manufacturers (and therefore the consumer) to supply ICC/ICM profiles for every ink/paper combination in distribution. To make things worse, printers have a much greater variation in performance than your average monitor.

How to get ICC/ICM profiles

Monitors: If you didn't get a profile on an installation or driver disk that came with your monitor, you may need to go to the manufacturer's web site to download one. You can check in your c:\windows\system\color folder for a file (they all have extension "icm") that has your monitor name/model. If one does not exist in that folder already, you can check the manufacturer's web site. If they have no specific link for ICC/ICM profiles, it might be worth downloading and installing any drivers designed for your monitor. Sometimes a manufacturer includes ICC/ICM profiles with a driver installation and does not tell you that this includes the profile(s) as well. If you simply cannot locate a monitor profile, all you can do is disable monitor color management and hope that the manufacturer designed the monitor to conform to sRGB space. You could also make your own monitor profile using a program like Profile Prism, WiziWYG (see below) or Adobe Gamma that comes with PhotoShop. The demo version of WiziWYG allows monitor calibration without purchasing the full version. This type of profile is normally more limited than a "full blown ICC/ICM profile", but in some cases, can result in a noticable inmprovement in image quality.

Printers: There are some places to look for "ready made" profiles for your printer. Check the links below to see if a profile is available for your printer. Note that it is extremely important to follow any instructions that come with the printer profiles since proper operation depends on exact printer properties settings (such as DPI, high speed mode, etc.). For Epson printers, most (if not all) profiles require selection of "no color adjustment" as well.

Make your own profiles

Many imaging hobbyists and experts are using profiling tools like Profile Prism to create custom profiles for their devices. To profile a printer, a scanner is required to scan an included target along with output from your printer. The process takes only minutes to perform and the output is an "icm" file that you can use with Qimage or another ICC/ICM compliant application.

I have a profile for my monitor or printer. Now what?

For specific information regarding how to use ICC profiles on your system, check out our new section on color management.

How do these ICC/ICM profiles relate to Qimage?

You can think of the "Color Management" support in Qimage as a way to translate data from the "language" used by your camera to that used by your monitor/printer. If your camera was supplied with an ICC profile that describes the color used in it's JPEG/TIFF images or you purchased an ICC profile from the Qimage Plugins Center, and you have a profile for your monitor and printer, you can ensure accurate color on screen and in print. Color profiling is like using a road map. To describe how to get from one place to another, you must first specify the start and end location on the map. Software can then tell you how to get to your destination. Similarly, you need a start and end point to convert from one color space to another. In terms of ICC profiles, the start and end points would be an input profile (for your camera) and an output/device profile (for your monitor/printer). The following is an illustration of the flow of data using ICC profiles in Qimage (and many other software programs that are ICC aware). For specific examples of using ICC profiles in Qimage, see the "Help", "Contents", "Learn by Example" in Qimage's help file.

Note that Qimage uses the "Input Table" in the diagram above in lieu of embedded profiles. The input table is simply a way of "tagging" certain types of images with a certain ICC profile. If Qimage finds an ICC profile embedded inside your JPEG/TIFF images, it will use that embedded profile instead of looking for an associated match in the input table. These are simply two different methods that Qimage uses to associate ICC profiles with images: by association or specifically (by embedding).

Still Confused?

Don't feel bad if the above information doesn't "sink in" right away. Color management is something that can take up volumes and entire lifetimes to really understand it. Fortunately, Qimage gives you a simple interface to check out color management and test the results right away. Sometimes, the best way to get to know something is just to try it. Try to remember that profiles are only a type of "filter" that you can use to improve the color accuracy of your images. When in doubt, try it out! Print a small 3x2 version of an image to your printer using Qimage without printer color management. Then turn color management on and select the appropriate profile for your printer, make sure the settings are correct, and print another 3x2 right next to it to see how they compare. This is simple to do with Qimage: on the second "run", just add the "Template" at the bottom of the thumbnails to the queue first and that blank template will cover where the first image printed. Then add the image to the queue and print it on the same piece of paper. The new "test" image will be right next to the first.

How to Apply Color Management Concepts in a Workflow

The above outlines the basics of what color management and ICC profiles are. To learn more about how to apply these concepts in the "real world", check out our new section on color management and it's application to different workflows.