Your camera, your computer monitor, your projector, your printer, your friend’s monitor, even your eyes all see color slightly differently. The business of resolving these differences is called color management.
The process is simple in principle. A “standard” color space is defined, independent of all the devices. This color space is an internal abstract and is not observed directly, but is the internal representation in our computer of the image. Now, if we want to display the image on, say, our monitor screen, we must convert the color values from the internal representation to new values (corrected RGB values) that will appear correct when displayed on the monitor. To do this, the operating system color management software (or that in a color aware program such as Photoshop) uses the ICC Profile for the monitor, which you can think of as a mapping function, to adjust each pixel’s color before display. Each device has its own, unique ICC Profile, obtained from the manufacturer, or, better, created by you, using a device such as the X-Rite Eye One, or Datacolor Spyder. For a more detailed overview of color management, with illustrations, see this Overview of Color Management by Cambridge in Colour .
Since the “standard” color space is defined by the ICC, all device profiles are created relative to a single, universal standard. This means that if I have an image in my color managed computer and bring it to your house, where you also have a color managed computer with a profile for your monitor, the image should appear exactly as it did on my machine. It also means that if I have a “good” profile for my projector, the image that I meticulously color corrected should appear the same when projected for competition.
There is a caveat. Not all devices can reproduce the full range (gamut) of colors visible to the eye. So that beautiful, saturated, morning glory blossom that you saw on your (wide gamut) monitor may not print or project well. It’s simply beyond the ability of the end device to reproduce the necessary colors and/or brightnesses. That wonderful image may appear dull or washed out. (The really saturated blues and reds are most problematic. Printers often have trouble with yellows.)
When you’re printing, you may be able to slightly improve the appearance by choosing a different “rendering intent.” These tell the computer how to map those colors that are “out of gamut” back into the printable color space. If, for example, you choose perceptual intent, all of the blues in that morning glory are proportionally interpolated down in saturation until they fit within the printer’s gamut. This changes the overall color of the image, but the effect is usually quite subtle. For many devices, the rendering intent is not under user control, as it is fixed when the profile is created.
Back to projection- the projector also has smaller gamut than your fancy monitor. So there’s bound to be some disappointment if you like really bright, saturated images. While there’s no way to make the image project with the full, vibrant color that you see on your monitor, it is possible to know in advance what you’re going to get. The method relies on the “soft proof” technique available in Photoshop and other image editors. Here, you apply the profile of the projector to the image and view the result on your monitor- theoretically just what you’ll see from the projector. In Photoshop, you can actually edit the proofed image, so you can make contrast and color adjustments to optimize the final appearance on the projector. Soft proofing is also highly recommended when printing. The color profile for the Canon projector we use for club competitions can be downloaded here in a zip file format. While you can use this to “soft proof” your images, when you save a file ready for competition, just use the normal sRGB format for the JPEG. The competition software and the projector profile that we use will do its best to display it properly.
There is another factor that should be mentioned in any discussion of color management, and that is control of brightness/luminance. The same image, when viewed under widely differing brightness conditions, will appear different. The situation is especially pronounced when comparing prints (a reflective technology) to the monitor (an emissive technology). About the only way you can get your prints to appear the same as your screen is to use a “standard” luminance on the screen, and to carefully control the brightness of your print viewing light. Many profiling packages will allow you to adjust the monitor luminance. If so, you might try a setting of ~90 cd/m2 when you profile the monitor. For a deeper look into this subject, see http://www.metalvortex.com/chart/ . You can use some colorimeters or light meters to adjust the distance of the viewing light to give a similar brightness when viewing a white sheet. Pay attention also to the color of the viewing light- make it about a D50 (5000K). Don’t forget to work in a darkened room for good color and lightness. And remember that the image you’re trying to match is the soft proof, not the original.
Probably the best way to adjust the projector brightness is with step wedges and images especially prepared to test color and separation of tones. We do this, both before and after profiling, with the competition projector. What you’re looking for here is a uniform step wedge, with separation in the lightest tones, and the same in the darkest steps. The profiled color test images, especially the grays, should then appear “normal”.
It’s beyond the scope of this note to get into attaching profiles to images and why you might want to do so, or choosing a color space for Photoshop (Adobe RGB or Prophoto RGB are adequate). There are also potential complications if you are working from a Windows computer and using other than Photoshop, Elements, or Lightroom. Depending on your editing and/or display software, your monitor profile may not work, resulting in your computer NOT being color managed, even though you have made a profile. The references may be of assistance.
The test images, which you may download below, should be displayed from one of the above programs, or another that is known to be color managed.