A client of mine is a professional photographer. Among other items, she sells gorgeous, full-color photo notecards of a myriad of multicolored flower species.
Quality is paramount with this client—understandably.
She recently received digital (inkjet) proofs of eight of her cards from a commercial printer with a small-format 4-color press. The contract proofer had been “fingerprinted” to the vendor’s press, so the digital output my client saw would very closely resemble the final offset custom printing of her cards.
She was unhappy with six of the eight prints. “Too dark,” she said.
Fortunately, this client is a consummate professional. She had submitted 8-bit TIFF images in CMYK color space, which I had placed in InDesign files and then distilled into “press-quality” PDFs. My client took responsibility for the error and requested second proofs prior to printing. She looked closely into the process to determine exactly what had happened, prior to adjusting the files and resubmitting them to the custom printing vendor.
Possible Causes of the Problem
First of all, the highlights and mid-tones were acceptable. Only the shadows of the photos concerned my client.
My client works in her basement, so she can control the ambient light in the room (i.e., the room light does not change as the sun rises and sets). She also calibrates her monitor regularly to ensure color fidelity. Both of these steps are essential, but most people (I would venture to guess) do not do either with the necessary frequency and precision.
As an additional consideration, LCD monitors, which most designers possess, “run hot.” This term, provided by a commercial printer with whom I used to work, means that colors on an LCD monitor appear lighter and brighter than they will appear in an actual custom printing job. It is all too easy to forget that an image on a computer monitor created with red, green, and blue light will not exactly match the image printed with ink—or even toner—on paper. However, knowing that images on an LCD monitor will print darker than they appear will help you avoid mistakes.
Using her knowledge of color and light, my client determined that the problem had occurred in the conversion from the RGB color space to the CMYK color space prior to her sending me the photos. For whatever reason, the color shift appeared most intensely in the shadows during the translation from RGB to CMYK. It is good to keep in mind that scanners usually capture images within a Red/Green/Blue (light-based rather than ink-based) color space. This is not as large a color space (does not include as many distinct colors) as “all visible color,” but is is larger than the Cyan/Magenta/Yellow/Black color space. It has a larger color gamut (number of reproducible colors).
For the most part, designers and photographers work within the RGB color space up until the last possible moment, and then convert the image to CMYK just prior to sending the job to the commercial printer. Colors that exist within the RGB color space and the CMYK color space transition without a problem. Colors that exist within the RGB color space but not within the CMYK color space shift to the nearest color match. This often causes a visible color shift.
Color Corrections and Final Proofs
My client determined that the problem had occurred during the color conversion. Therefore, she lightened the shadows in the RGB color space, converted the images to CMYK, and re-checked them to make sure the final CMYK output would be acceptable (accounting for the tendency of the monitor to lighten colors, and having confirmed the accuracy of the calibration of the monitor).
I received the amended 8-bit TIFF CMYK photo files and repositioned them within the InDesign art files for the photo notecards. The difference was dramatic. The images were lighter—but only in the shadows.
When the second set of proofs arrived, my client was happy. She approved them and released the job to the custom printing vendor for final production.
What We Can Learn from This
- Always color calibrate your monitor. Do this regularly.
- Control the ambient light in your computer room. The surrounding light will alter your perception of the color on the monitor.
- Assume that the final image will print darker than the image on the monitor. Ask your prepress provider at your commercial printer how to compensate for this using Photoshop’s “levels” and “curves” commands.
- Make your own inkjet proofs. Then, if these are ok, have your commercial printer make proofs. Adjust your files as necessary. It’s better to make—and pay for–multiple proofs than print the job too dark, too light, or with a color cast.
This entry was posted
on Monday, December 5th, 2011 at 12:17 am and is filed under Offset Printing, Postcard Printing, Prepress, Printing, Proofing.
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