Monday, April 13, 2009
Images are typically scanned or captured in RGB mode. When you start work with a colour image it is usually best to work in RGB mode, as this is faster than CMYK mode and allows you to use all of Photoshop’s commands and features, providing greatest flexibility.
The disadvantage of working in RGB mode, if your image will be printed, is that RGB allows a greater gamut of colours than you can print. At some stage, some of the brightest, most vibrant colours may lose their brilliance when the image is brought within the CMYK gamut.
Convert to CMYK when the image is to be printed and you have finished making changes.
To place a colour image in a page layout application from where it will be colour separated, you need to convert from RGB to CMYK. When you convert from RGB to CMYK, photoshop adjusts any colours in the RGB image that fall outside the CMYK gamut to their nearest printable colour. (See Chapter Five, ‘Defining Colours’, for details on gamut warnings.)
You can also select Display out of Gamut colours from the view menu, to highlight (in grey) areas of the image that are out of gamut.
Indexed Color mode
This mode reduces your image to 256 colours or less and is frequently used for multimedia and web images.
Duotone For details on using Duotone mode see page 60.
When you are not printing an image in colour you can convert to Grayscale mode to make working faster and file size smaller.
This mode uses the CIE Lab mode which has one channel for luminosity, an ‘a’ channel representing colours blue to yellow and a ‘b’ channel for magenta to green. A significant advantage to this mode is that its gamut encompasses that of both CMYK and RGB modes.
This mode reduces everything to black or white pixels. The image becomes a one-bit image.
Multichannel mode uses 256 levels of grey in each channel. When you convert RGB or CMYK images to multichannel mode, the original channels in the image are converted to spot colour channels. Multichannel mode is an advanced option-only use it if you have a detailed understanding of the printing process.