Some Technical ThingsJanuary 27, 2011
Here are some of the things we've talked about in class for far.
Bleeds are 1/8 inch
Half-tone screens/Color separations: is a field of dots to simulate tone in the laser and off-set printing technologies. Half-tone screens are measured in dots per inch (dpi). Resolution of a digital image (pixels per inch – ppi) must be at least 200% of what the line screen (dpi) is measured. Magazines are typically off-set litho printed in a line screen of 133 to 150 dpi. Newspapers are typically 85L to 100L. Custom offset litho printing can range from 133, 150 or even 200L. So if you are printing at 133L (dpi) the resolution of a digital raster image should be at least 266 ppi.
Import formats for InDesign: tiff (tagged image file format) and eps (encapsultate postscript). A tiff is a raster file format – pixel based. The data in a tiff even if the graphic/image is produced in a vector program like Illustrator is translated into raster (pixels) and is resolution dependent. An eps can be either raster or vector. Raster images (photoshop) saved in eps format are still resolution dependent, so be wary of enlarging a raster eps file in InDesign – you are lowering the resolution of the image when enlarging. Vector (Illustrator) graphics saved in eps format are resolution independent and can be enlarged without quality loss in InDesign. Photoshop eps files tend to be larger (digital data) than Photoshop tiff files.
CMYK: The four process colors… Cyan, Magenta, Yellow and Black – These four colors are used to reproduce/print full-color images. Each color has a printing plate (off-set litho) with color separations (screens of varying sized dots) overlapping each other to create the illusion of full-color.
Spot Colors: A physically mixed color from multiple colors. This mixed color is then applied to the litho press to be printed. Spot colors can be included along with the process colors. One additional spot color along with CMYK would make for a 5-color print job. Two additional spot colors would be a 6-color print job.