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Tricks for Fixing Bad Images

(September 2003) posted on Thu Sep 25, 2003

Coudray describes techniques you can use to overcome resolution, color, image-quality, and file-format issues.

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By Mark A. Coudray

In the early days of digital scanning, all files were prepared as CMYK. This was because CMYK was the only way full-color printing was done on paper. So scanner manufacturers, such as Crosfield, Hell, and Dainippon, all made their scanners generate native CMYK files.


The problem is that CMYK for paper is not what we need for screen printing. The tone curves, dot gain, gray balance, and ink densities are all different. Every printer I know has experienced the joy of having to make someone else's CMYK scans print. Most of the time, it simply does not work. Thankfully, this problem is beginning to go away.


Color management systems (CMS) began to take a serious foothold about four or five years ago. The technology was around before that time, but not enough companies used it to call it a productive solution. As drum scanning has given way to desktop scanning and digital photography, CMSs also have really changed. CMSs use an RGB workflow. The image is acquired in RGB and then converted using a device profile for a specific CMYK device. This means that while an image printed on a printing press has a different profile than, say, an Epson 9500 inkjet proofer, the image will look the same on either device if the CMS profile is properly prepared and applied.


The heart of the CMS is the use of profiles. As you begin to study and understand how profiling works, it is possible to do profile-to-profile conversions. This allows for the conversion of an image prepared under one profile to be converted to fit the profile of a new device. It is complicated, but completely achievable for the knowledgeable prepress technician. The CMS workflow is continuing to evolve, and it is getting more and more understandable.


Poor image quality


For the sake of this discussion, poor image quality has to do with image defects, tone, and contrast. It also may involve color correction and cast removal. While each of these subjects warrants an article of its own, I'll just focus on the essentials here.



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