title: “A different image for a different paper” date: “2000-06-17 14:00:00” layout: post tags: [ historical, fonts, typography ] —
This post was originally published on TheMacMind.com
Scanning images into your computer is just the first step when preparing images for printing. Adjusting the image for appropriate printing conditions is essential to maintain top quality and correct colors.
How many of us have had beautiful color images on our screens and received muddy looking prints when the shiny wrapped packages return from the printer? Unless you have a good relationship with your printer and they call you mid-run, it’s actually quite common. With a little planning and know how all your images can and will never look muddy again. Here are a few tips to ensure your images will turn out crystal clear.
What to Do
- Convert your RGB images to CMYK.
- Determine the paper stocks and what process you will use.
- Modify files differently to suit every job.
Converting to CMYK
Most scanners produce images in RGB format. The RGB (Red, Green, Blue) file format is an additive color process where adding each of the calories together brings you closer to white. Mechanical printing process however, such as offset lithography, use a subtractive process where removing the colors gives you white.
When you first convert your images to CMYK (Cyan, Magenta, Yellow and Black) you may notice slight changes in the bright colors. The shift in the range of colors is known as a gamut shift. RGB and CMYK use slightly different color gamuts. If you notice a change, this means the modified color was outside the CMYK color gamut and could not have been printed using the regular CMYK process. The conversion software simply replaced the unprintable color with the closest match inside the CMYK gamut. For an example, take the following image of the colored dots and convert it to CMYK. You’ll notice some of the colors will change because they can’t be printed with CMYK.
Modifying your files
When printing an image on a lithographic press, there is always some amount of dot gain. The tiny dots in the image will increase slightly and thus make the image appear darker, with the most apparent increase in the midtone area. To compensate for this you need to adjust your original image accordingly. In general, the following dot percentages are required for printing images:
NOTE: These numbers are provided as a general guide. Consult with your printer to achieve the best results on their printing press.
To see how your images stack up, you can check using an application such as Adobe Photoshop. Once your images are in CMYK, set the info pallet to display CMYK pixel information and then explore the different areas of your image. The Highlight is the lightest area of the image that contains some amount of detail. The shadow is the darkest area of the image and the midtown is the neutral gray area of the image. Not all images contain a highlight, midtone and shadow area so move around your image and check the various areas.
If your image is “high key” or contains mainly highlights such as a snowy forest, you may wish to increase the midtone values by about 5%. Likewise if your image is “low key” or very dark, you may wish to lower the midtone values by about 5%. You can adjust these values by using the “Adjust Curves” feature in Adobe Photoshop.
While adjusting and modifying your image continually check it to make sure it still looks good. Simply following the numbers won’t guarantee good results but if the image looks good on screen and the numbers are close, you’ll have much better results when you receive the final prints.