Print Publishing Guide

Objects appear to be certain colors because of their ability to reflect, absorb, or transmit light; we perceive this light as color.

Brightness has to do with the quantity of light reaching your eye - the brightness of a surface depends on how reflective it is.
Hues depend on wave length and are identified by color names.
Saturation, sometimes called chroma, refers to a color's vividness.

Spectral colors - the colors of a single wavelength of light from a prism - have maximum saturation.

RGB (blue, green, blue) are the additive primaries of light, combine 100 percent of red, green, and blue light, white color is perceived, if none of the additive primaries are present, black color is perceived.

red + blue = magenta
red + green = yellow
green + blue = cyan
red + blue + green = white

CMYK (cyan, magenta, yellow, black) are the subtractive primaries, they filter components of red, green and blue from white light and what remains will be perceived. In theory, we combine 100 percent of cyan, magenta and yellow ink on paper, the result is black. However, because of impurities in printing ink pigments, black ink is added to compensate for that to get black color.

cyan + magenta = blue
cyan + yellow = green
magenta + yellow = red
cyan + yellow + magenta = muddy brown
cyan + yellow + magenta + black = black

DPI is the abbreviation for dots per inch

Dot gain increases halftone dot size, occurs naturally when wet ink spreads as it's absorbed by the paper.

ppi is the abbreviation for pixels per inch. For best results, use a image resolution that is greater than the printer's resolution ( a factor of 2x is appropriate).

When two objects or colored regions that overlap each other, a designer can choose either to let the top object eliminate, or knock out, what is beneath it or to allow overprinting.

lpi, also called screen ruling or screen frequency, is the number of halftone dots per linear inch used to print grayscale or color images.

When process-color separations are printed, the arrays of dots for each color are oriented at different angles to minimize interference patters. The screens are positioned so that the dots form a symmetrical pattern called a rosette, which the human eye merges into continuous-tone color. The relationship between the screen angles is critical. Occasionally, a pattern in a photo interferes with one or more screen angles, causing a noticeable pattern of interference lines called a moiré pattern. These patterns are also caused by attempting to print photos that have been scanned from already-printed material.

color trapping: adjacent color are intentionally set to overprint along common boundaries.

Frequency-modulated screening (also called stochastic screening) arranges dots in irregular clumps rather than in an orderly formation. Screens made this way don't have repeating beats and are generally free form moiré patterns. Traditional halftone screening uses the size of the dot to modulate between gray levels: larger dots for darker shades, smaller dots for lighter shades. FM screening controls the level of gray or color by varying the composition of clumps and how close the clumps are to each other.

Use spot colors when:

You need one or two colors, and you won't be reproducing full-color photographs.
You want the effect of special inks, such as metallic, fluorescent, or corporate color inks. These are often colors that can't be reproduced with combinations of the process color.
You want to print logos or other graphics elements that require precise color matching, or you're printing large areas of color throughout a publication and you want to ensure color consistency.

Use process colors when:

You need more than two colors in your publications. Printing with process color inks (CMYK) cost less than printing with three or more spot inks.
You want to reproduce full-color photographs or color artwork that can only be reproduced with process colors.

Use spot and process colors together when:

Your requirements extend beyond process color printing.

Because process black is transparent, the addition of another process color to black is often beneficial. A rich black ink combines process black ink with one or more of the other process ink to achieve a more intense black.

Use a single, solid ink (such as 100 percent black or a dark spot color) to print hairline rules and small text. Fine elements printed with two or more colors are difficult to print in register.

Avoid creating process colors with high total ink coverage. Higher total ink coverage may prevent the ink from drying correctly and can cause set-off, where the ink from one sheet of paper is transferred to the next sheet in the pile.