Monday, June 18, 2007
The Futility Of CMYK
Myth: A big color space with 16-bit color guarantees visibly better results on a printed page
I wish that were true. The printed page can be a frustrating place for a photographer. Sometimes images look better there, sometimes worse. Like many photographers, I once thought a publication simply took an image, “translated it” into printing plates of some sort, then worked to match the photo to the page. With that line of thinking, it's easy to then believe that a photo should perfectly match its printed version; if it doesn't, someone screwed up.
Truthfully, those who put together any publication are generally pros who want the best for it. Art directors and designers want their work to look good. Pre-press technicians want their work to result in good-looking pages, or their customers don't come back. Printing press operators are generally old-school craftspeople who treat printing as an art.
So with all these professionals aiming to get the best from the printed page, a large color space and 16-bit color should result in the best of color. Right?
Two major roadblocks: CMYK and the nature of the printing press. CMYK is a very limited color space relegated to printing. It separates the colors cyan, magenta and yellow from black (K) to allow color photos on a page to be produced by a big printing press. I've had firsthand experience with thousands of images that have gone from any RGB space to CMYK, and let me tell you, it sometimes isn't pretty.
With this CMYK file, printing plates are created for the printing press. Most publications today are printed on a web press, a high-speed printing press that uses a revolving cylinder to apply ink to paper that rolls rapidly through the unit.
The ink has to be laid down in just the right amount onto these speeding rollers, then rolled off onto the paper and reapplied to the rollers for the next page, all at a very high speed (many thousands of impressions an hour). The press operator monitors and works these machines to ensure the pages are printing properly. A small tweak (either deliberate or due to machine error) can affect thousands of pages before it can be changed. The lowered precision that comes from the combination of CMYK and the operation of a printing press can make subtle image processing a futile exercise. Lower-quality printing papers, such as newsprint, exacerbate this problem.
We see this in magazines all the time. We try to show a great little effect in Photoshop or a nuance in a photographic technique, then when it goes to the printed page, the reader has trouble seeing it. I recently completed a book on Photoshop (Outdoor Photographer Landscape and Nature Photography with Photoshop CS2) and “showed” some wonderful effects, yet when the book came out, readers wondered about certain examples. CMYK, plus the paper used, mellowed many differences.
Having all the potential of 16-bit and large color spaces can therefore result in no readily discernible difference from a quality 8-bit sRGB file when both files go to press. That said, having 16-bit Adobe RGB capabilities can be extremely useful. They offer a range of correction and adjustment that can make it possible to do certain image processing not readily done with 8-bit sRGB (and that will show up on the page). Plus, when this happens, you may get a cleaner image for print because of the extended tonal and color range available.
However, for some purposes, that high-quality, 8-bit sRGB file can be more than enough and faster to process. Remember that a JPEG file is a camera-processed RAW file done quite smartly. This is why many photographers now shoot RAW+JPEG (sRGB). They can always get 16-bit Adobe RGB color from the RAW file, but they can also get a quality quick image (or fast batch processing of many photos) as needed.
The bottom line is the right tool for the job. I know a fine professional wildlife photographer who has been frustrated with digital because he felt he had to deal with RAW files. Yet his camera is capable of superb JPEG images that better fit his workflow. Because he does minimal in-computer processing, these JPEG files will print absolutely equal to anything he'd get from RAW, but with a workflow that is much more efficient for him.
CMYK and the printing press are great modifiers of the image—more than any simple difference that comes from RGB color spaces or 8-bit vs. 16-bit color. Simply using one color space and 16-bit doesn't guarantee a better printed image.