Softwares and print

Illustrator

• If you make a swatch global it means any object you draw with that colour with change if you alter the CMYK values of that swatch.
• Process colours will be printed in CMYK.
• Spot colours can be cheaper as only one plate is needed ( if only mono) rather than CMYK plates.
• In Illustrator if you save swatch library as AI it can only be opened in Illustrator, but if save as ASE, it can be opened in other applications such as InDesign and Photoshop.

Photoshop

• The gamut for RGB is greater than the gamut for CMYK. Also there are more edit possibilities in RGB images when using Photoshop as it is native mode.
• Using 'view' 'gamat warning' will show areas which are out of printable range (CMYK) and I can then use 'replace colour' to adjust the selections out of range. See image 1&2.
• Alternatively you can use 'view' 'proof colours' and when in this mode, the image is still RGB (so can achieve all filters) but all the colours used are all in printable gamut.
• By changing the curve of the spot colours in a duotone, it affects how much impact each colour has. See image 3. If using a duotone image it is better to use spot colours as this will mean less plates for the printer.
• To do overlayed type while still keeping the brightness of colour (loss in transparency) can create a new spot channel and edit the solidity - only on greyscale. See image 4.

Image 1. Gamut warning.

Image 2. Replace colour.

Image 3. Duotone curve.

Image 4. New spot channel.

INDESIGN

• To check colour separations go window, output, separations preview. See image 2-6.
• By doing this you can also screen print. 
• Also we can print the separations by selecting it in the print menu. See image 7.
• Overprint can be done by selecting window, output, attributes. See image 8.
• However there is an ink limit. Too much ink on the page can make paper heavy and cause problems. This can be checked in the separations preview by selecting ink limit. See image 9.
• When screen printing (not as needed in digital printing) trapping is sometimes a good idea. Add a stroke to the lightest colour.

Image 1. All colours.

Image  2. Cyan separation preview.

Image 3. Magenta separation preview.

Image 4. Yellow separation preview.

Image 5. Key separation preview.

Image 6. Spot separation preview.

Image 7. Printing separations.

Image 8. Overprint fill.

Image 9. Ink limit.