Adobe Photoshop CS5 for Photographers - Martin Evening [269]
Go into any TV showroom and you will probably see rows of televisions all tuned to the same broadcast source, but each displaying the picture quite differently (Figure 12.2). This is a known problem that affects all digital imaging devices, be they digital cameras, scanners, monitors or printers. Each digital imaging device has its own unique characteristics, and unless you are able to quantify what those individual device characteristics are, you won't be able to communicate effectively with other device components and programs in your own computer setup, let alone anyone working outside your own system color loop.
Figure 12.2 While some digital devices may look identical on the outside, they'll all have individual output characteristics. For example, in a TV showroom you may notice how each television screen displays a slightly different colored image.
Some computer displays have manual controls that allow you to adjust the brightness and contrast (and in some cases the RGB color as well) and the printer driver will also allow you to make color balance adjustments, but is this really enough? Plus, if you are able to get the display and your printer to match, will the colors you see on your display appear the same on another person's display?
Color vision trickery
They say that seeing is believing, but nothing could be further from the truth, since there are many interesting quirks and surprises in the way we humans perceive vision. There is an interesting book on this subject titled Why We See What We Do, by Dale Purves and R. Beau Lotto (Sinauer Associates, Inc). There is also a website at www.purveslab.net where you can have a lot of fun playing with the interactive visual tests, to discover how easily our eyes can be deceived. What you learn from studies like this is that color can never be properly described in absolute mathematical terms. How we perceive a color can also be greatly influenced by the other colors that surround it. This is a factor that designers use when designing a product or a page layout. You also do this every time you evaluate a photograph, often without even being aware of it.
The versatility of RGB
A major advantage of working in RGB is that you can access all the bells and whistles of Photoshop which would otherwise be hidden or grayed out in CMYK mode, and if you use Adobe RGB or ProPhoto RGB, you will have a larger color gamut to work with. These days there is also no telling how a final image may end up being reproduced. A photograph may get used in a variety of ways, with multiple CMYK separations made to suit several types of publications, each requiring a slightly different CMYK conversion (because CMYK is not a ‘one size fits all’ color space). For example, high-end retouching for advertising usage is usually done in, RGB mode and the CMYK conversions and film separations are produced working directly from the digital files to suit the various media usages.
Photographers are mainly involved in the RGB capture end of the business. The proliferation of Photoshop, plus the advent of high quality desktop scanners and digital cameras, means that more images than ever before are starting out in, and staying in, RGB color. This is an important factor that makes color management so necessary and also one of the reasons why I devote so much attention to the management of RGB color, here and elsewhere in the book. So, if professional photographers are more likely to supply a digital file at the end of a job, how will this fit in with existing repro press workflows that are based on the use of CMYK color? Although digital capture has clearly taken off, the RGB to CMYK issue still has to be resolved. If the work you create is intended for print, the conversion of RGB to CMYK must be addressed at some point, and so for this important reason, we shall also be looking at CMYK color conversions in detail later on in this chapter.
Beyond CMYK
There are other types of output to consider, not just CMYK. Hexachrome is a sixcolor ink printing process