The resolution of an image is expressed in terms of “dots per inch” (dpi) or “pixels per inch” (ppi). Line screen is expressed in terms of “lines per inch” (lpi). For grayscale or color art to reproduce correctly, the resolution should be approximately 1.5 to 2 times the line screen to be used at 100% of the placed size. This means it is very important to make proper calculations if you will be enlarging your graphic by a significant amount. For instance, if you intend to scan your graphic at 100% of its original size, but place it in your layout application at 150% of its original size, you should scan your graphic at 450 dpi when using 150 lpi for the best quality output.
Below is a guideline for the required resolutions at 100% of their placed size:
Scanning at a resolution over 2x will not improve image quality and in some cases will even degrade it. It will also create files much larger than needed which will slow production time. It is truly best to scan your image at the correct size and resolution that will be used. This will allow for easier management and storage of your files.
One-Color Line Art
One-color line art such as a logo or pen-and-ink drawing–should be scanned at 600-1200 dpi at 100% of its final size.
Halftones: Highlight and Shadow ValuesThe scanner operator or retouch artist should maintain the following values:
Never make adjustments based on screen appearance or laser prints–an image that looks great on screen will often lose detail in the highlights and shadows. Instead, please refer to the specifications provided above.
Compatibility & Fonts
Working With Color