Help:Manual Cmsrenderintents

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Color management with Scribus, an Introduction Part 3

Rendering Intents

The other puzzler for newcomers to color management is rendering intents. Your choice of rendering intents is a way of telling littlecms how you want colors mapped from one color space to another.

Perceptual - This rendering intent maps color "smoothly", preserving relationships between similar colors. This prevents "gamut clipping" with its potential loss of detail and "tonal banding" problems. Gamut "clipping" happens when two or more colors that are different in the input image appear the same when printed. Perceptual rendering intent makes small adjustments throughout the image to preserve color relationships. It sacrifices some precision of colors in order to ensure pleasing results. For photographic images and scans, this is usually the best choice for a default setting.

Perceptual intent will produce the most predictable results when printing from a wide range of image sources, for example, when printing RGB images on CMYK devices, or when trying to match CMYK devices that are radically different from each other. Consider this "foolproof" setting to be best for users who handle the wide variety of images that commonly enter large format printing facilities.

Saturation stands for logos, spot colors, etc. It tends to preserve the amount of, or vividness of colors. But it can make photos look ugly. If you were working with logos with a specific shade, saturation will bring better color matching, as far as you give more importance to the color than to the image.

Absolute Colorimetric: When a color is not printable within the "gamut "of the output device, this rendering intent simply prints the closest match. It reproduces in-gamut colors without compromise, as faithfully as possible. This produces the most accurate matching of spot colors. Unfortunately, it can also result in "gamut clipping" where two colors that are different in the original are identical on the print. White points are similarly clipped, then causing color relationship problems in the highlights of images. This type of clipping, and the resultant problems, typically make this rendering difficult to use with anything but spot colors . Some users will be disconcerted with a yellowish cast in their image, but this intent is measured in highly controlled lighting conditions with a D50 light box. This often has a "warmer" temperature than more typical viewing conditions. This rendering intent is almost exclusively used when a corporate logo or color must be matched exactly regardless of media. Kodak yellow would be a good example.

Relative Colorimetric: When a color is not printable within the gamut of the output device, this rendering intent prints the closest match along with an adjustment that maps white to the paper of the output. This mapping of "white point" prevents the problems of "Absolute Colorimetric" with images that will not be printed with spot colors. When producing color proofs on RGB ink jet printers, while simulating CMYK printing presses you can use this intent, if you know the intended precise profile. Users of Adobe Press Ready will understand this concept quite well. This approach works well when you have accurate embedded profiles in images being converted to CMYK space with printer profiles that have been very precisely profiled with color measurement devices. These are typically scanner or more rarely in digital cameras, and is most likely when someone has spent a lot of time and effort to finely calibrate and profile their equipment. It takes sophisticated ($$$) color calibration equipment to measure the printer under fairly well controlled conditions.

Other CMS Options

Mark Colors Out of Gamut is a setting which will show colors in your document which may be outside the gamut, or printable color range of your printer. Note, this is only a warning, as the current ICC specs do not define this uniformly. This is a function available from littlecms.

Final Printing with Scribus

For Scribus users, there are a couple of options for printing with a color managed intent.

When printing, Scribus can optionally apply the printing profile you have chosen in the color management panel. This can be very useful, if you want to simulate a commercial printer profile with your ink-jet printer via CUPS.

PostScript Output - This would require having your images tagged before being placed in Scribus files when outputting a Scribus document either: as pure postscript or as individual EPS files. Scribus uses level 3 postscript.Level 2 and Level 3 postscript can read and use icc profiles within an image. Most color postscript devices will read the embedded profiles and use them to render color within the postscript using something called a rendering dictionary.

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