DPP Home Software Image Processing Color Space In Black-And-White

Tuesday, October 27, 2009

Color Space In Black-And-White

What is a color space, which options are best to use, and how can you make your own custom profiles to get the most out of your chosen color space?

Available Color Spaces
In general, you can choose from five working space profiles: Apple RGB, Adobe RGB, ColorMatch RGB, ProPhoto RGB or sRGB. There isn’t a universal “best” choice for all photographers, so you need to consider your particular workflow when deciding which to use as your standard working space.

To simplify your decision-making process, you can immediately eliminate Apple RGB and ColorMatch RGB from consideration. These color spaces were designed to encompass the range of colors that could be reproduced using what would now be considered ancient computer monitors. Just pretend like these color spaces don’t exist.

That leaves only three color spaces to choose from, and each of them represents a good choice for specific photographers based on their workflow.

sRGB. Of the three color spaces you’ll want to consider, sRGB has the smallest color gamut and is often cited as being inappropriate for photographers to use with their images. I’d certainly agree that sRGB is far from ideal for most photographers when it comes to choosing a working space, but for certain photographers, it may be the best choice. For example, many wedding photographers don’t produce their own prints, using a lab to generate that output. Printers such as the Fuji Frontier utilize an sRGB color space for printing, and the colors this printer can produce lie almost entirely within the sRGB color gamut. In such a case, there’s no real benefit to working in a color space with a wider gamut, making sRGB a good choice.

Adobe RGB. The Adobe RGB color space was originally created to encompass the range of colors that can be produced by the typical offset-press printing process and continues to serve as a workhorse color space for photographers. While the Adobe RGB color space certainly has some shortcomings for the photographic workflow, those shortcomings aren’t particularly significant for most photographers. For many (if not most) photo inkjet printer and paper combinations, Adobe RGB will encompass the color gamut of the printer fully, meaning Adobe RGB contains all colors (or nearly all colors) you can produce in print. As a result, it continues to be an excellent choice as a color space for a photographic workflow.

ProPhoto RGB. The ProPhoto RGB color space recently has become popular, and for good reason. ProPhoto RGB is an especially large-gamut color space that’s so large it includes many colors that don’t exist in the visible spectrum. This is a bad thing, in some ways, because it means color values within ProPhoto RGB are wasted on colors you can’t reproduce and, in fact, it’s possible that you could apply adjustments to your images that would result in colors that can’t be displayed or printed by any device. That said, if you want to ensure you’re taking full advantage of any device you might use now or in the future to generate output from your images, ProPhoto RGB is your best choice. The only serious caveat with ProPhoto RGB is that you should work in this color space only with 16-bit-per-channel images. If you use ProPhoto RGB with 8-bit-per-channel images, the risk of posterization is quite high due to the relatively large steps between colors in such a wide-gamut color space.

Building Custom Profiles

To help ensure you’re getting the best output from the images you’ve optimized in your chosen color space, you’ll need accurate custom profiles for the devices to be used to present your images.

The first step is to calibrate and profile your monitor display to ensure what you see on that display is an accurate reflection of the color information in your images. Without taking this step, you can’t be confident that the adjustments you make to the images will be accurately reflected in the actual image data. A variety of tools are available for monitor calibration and profiling, and the process is a simple matter of following the on-screen instructions and positioning the colorimeter (a device that measures the color output of your monitor) against the display so measurements can be taken and a custom display profile created.

Producing an accurate print of the highest quality requires a custom printer profile specific to the printer, ink and paper combination you’ll use for a given print. The process involves printing a series of color swatches and measuring the results with a device called a spectrophotometer. While you can get excellent results creating such printer profiles yourself, the tools are relatively expensive. You can save considerable money (on the assumption you only need a handful
of profiles) by using a service that builds a profile for your specific printer.

Among the variety of services available are those from Cathy’s Profiles (www.cathysprofiles.com) and color-management guru Andrew Rodney (www.digitaldot.net).


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