These also assume no dot gain and a perfect match of the color gamuts, independent of substrate.
- Unfortunately, these assumptions are not true for any real printing inks.
- Prior to electronic methods, elaborate manual methods of correcting for non-ideal inks were developed including manual hand etching of films and film masking. Some of these were incorporated into early scanners.
- The actual conversion equations are complicated and highly nonlinear. They are computationally intensive enough that often a color look up table (CLUT) is employed rather than calculate each value every time.
- Photoshop handles all conversions based on the best match the CIELAB values.
- To convert from RGB to CMYK it first converts to Lab and then from Lab to CMYK. (These transformations each may use CLUTs, but for our purposes this can be thought of as a numerical analysis problem.)
- This is then based on a device independent representation, but still depends on the assumed properties of the monitor and inks. We’ll illustrate this again with the color picker.
- PostScript Level 2 supports the use of CLUTs as well as transfer functions (nonlinear corrections for the output device).