Graphic Production Process Control III Additive vs. Subtractive Additive Color is used in photography, television, and computer monitors. Subtractive Color is used with pigments, such as Color Theory & Reproduction paint or ink. by Dr. Jerry Waite UNIVERSITY of HOUSTON Communicating about Color Start at the Beginning Printers and buyers need to understand that Color comes from light. color systems impact the way a colored object – Without light there would be no color. appears. – If you doubt this, try viewing color in a room without light! Objects created using different color systems Objects do not “have” color. will look different – no matter what! – They can either reflect or absorb the light that strikes them. Sources of Light Natural Light All light originates from the sun. The sun gives off many different waves of “Natural” light comes directly from the sun. electromagnetic energy. “Artificial” light usually comes from the burning Humans can see, hear or feel waves of different of some solid or gas. lengths. The sun’s waves are arranged by length in the electromagnetic spectrum. Page ‹#› The Electromagnetic Spectrum Primary Colors of Light Red, Green and Blue – Blue waves are approximately 500 millimicrons in length – Green waves are approximately 540 millimicrons in length – Red waves are approximately 640 millimicrons in length Called the additive system – Addition of electromagnetic waves results in stronger heat, sound or light. This system is used in computer monitors, cameras and color scanners. Combining Combining Primary Colors of Light Primary Colors of Light Red + Green = Yellow Red + Blue = Magenta – Yellow is a “secondary” color of light – Magenta is a “secondary” color of light Combining Combining Primary Colors of Light Primary Colors of Light Blue + Green = Cyan Red + Green + Blue = White – Cyan is a “secondary” color of light ONLY natural light is white – Only when the atmosphere allows it to be. Page ‹#› What about Black? How Objects are “Colored” Black is when no waves of light are combined. Light strikes the object Black is the absence of all color. – Some waves of light are absorbed by the pigment in the object Does that mean that black objects aren’t really – Some waves of light are reflected by the object there? No object “has” color – it can only absorb or reflect color that is present in the light. Artificial Light Sources Measuring Color of Light Sources Natural Sunlight W hite + UV + IR NA Degrees Kelvin (˚K) Flourescent Cyan Room lighting “W hite” flourescent “W hite” Color viewing Sunlight at Noon 6000˚ Kelvin Black Light UV Dylux Cool White 4500˚ Kelvin (flourescent) Incandescent Yellow NA Fluorescent Metal Halides Blues Plates, proofs “White” Fluorescent 5000˚ Kelvin Quartz-Iodine Yellow Process camera Incandescent ± 2700˚ Kelvin Pulsed-Xenon “W hite” Color cameras Lasers Vary Laser printers Colored Phosphors Red, Green, Blue CRTs Liquid Crystals Red, Green, Blue LCD Displays Effect of Light Source on Object’s Effect of Light Source on Object’s “Color” “Color” An object can only reflect that which it receives. Color Rendition Demonstrator A picture of yellow object in red lighting Judgment of color needs to be done under appears red. controlled lighting A picture of blue object in yellow lighting – 5000˚K is commonly used in printing plants. appears black. – Some buyers want to view color under same circumstances as end-user. – No matter what, there must be standardization. Use of RHEM light indicator. Page ‹#› Printed (Subtractive) Color The Subtractive Colors Printing processes do not use light waves to The pigments are colors Yellow, Magenta, and create color. Cyan. – The additive primary colors of Red, Green, and Blue are not Yellow, Magenta, and Cyan are the Subtractive used. Primary Colors. Printing processes use pigments to “subtract” – Note that the subtractive primary colors are the additive color from a substrate. secondary colors. Subtraction of Colors Subtraction of Colors by Pigments by Pigments Yellow ink reflects red and green light waves. Magenta ink reflects red and blue light waves. – These separate waves combine in the brain so that the – These separate waves combine in the brain so that the viewer sees yellow. viewer sees magenta. Yellow absorbs (subtracts) blue. Magenta absorbs (subtracts) green. Whenever you see “yellow” you are “not Whenever you see “magenta” you are “not seeing” blue. seeing” green. Subtraction of Colors Subtraction of Colors by Pigments by Pigments Cyan ink reflects blue and green light waves. Black ink reflects no light waves. – These separate waves combine in the brain so that the Black absorbs (subtracts) red, green and blue. viewer sees cyan. Whenever you see “black” you are “not Cyan absorbs (subtracts) red. seeing” any color. Whenever you see “cyan” you are “not seeing” red. No light is reflected, so no color is seen. Page ‹#› Combining Subtractive Colors Combining Subtractive Colors Printing yellow ink on white paper results in Printing magenta over yellow results in red. yellow. White - blue - green = red. White - blue = yellow. Combining Subtractive Colors Combining Subtractive Colors Printing cyan over yellow results in green. Printing magenta over cyan results in blue. White - blue - red = green. White - red - green = blue. Printing Colors on a Press Another Color Sequence "Black" "Black" Page ‹#› Another Color Sequence Reproducing Other Colors Halftone dots For example, orange is red + yellow Using ink, red is composed of yellow + magenta. "Black" To make orange using halftone dots, you need twice as large yellow dots as magenta dots – 2Y + M Proofing Color Kinds of Proofs Internal Control Digital preproof – to check for job’s color, image accuracy, and registration – Made from electronic files. External Control – OK for some internal control – for submittal to a client for approval – Does not accurately represent press sheet The goal of proofing is to accurately represent Contract proof what the press-sheet will look like. – Made from the same films as plates – The goal of a proof is NOT to look good. – More accurate representation of press sheet Digital Preproofs Digital Preproofs Softproof Black & White or Color Xerographic Prints – Computer monitor – Toner is not ink » Uses additive rather than subtractive system. – Resolution won’t match press » Monitors can be adjusted to change colors – Paper may or may not match press sheet Color Ink Jet Proofs – Inks do not match printing standards – Resolution doesn’t compare to press – Paper may or may not match press sheet Page ‹#› Digital Preproofs Contract Proofs Thermal Wax Single-color – Wax does not look like ink – May be used for internal or external control – Resolution doesn’t compare to press – OK for single-color work – Paper may or may not match press sheet – OK to check image position and accuracy Dye Sublimation – May be used to check color breaks – No halftoning effect – continuous-tone proof – Not acceptable to check accuracy of color – Paper doesn’t match press sheet Types – Velox-type photographic prints – Diazo-type “bluelines” – Polymer-type (Dylux) “bluelines” » can show color breaks Contract Proofs Overlay Contract Proofs Multiple-color Require a separate plastic overlay for each color – May be used for internal or external control Advantages – OK to check image position and accuracy – Available from many manufacturers – Shows color breaks – Relatively inexpensive & quick – May not be able to reproduce non-process colors, such as – Can be placed on actual press sheet PANTONE. – Can be used as a “progressive” proof Disadvantages Types – Overlays add a sheen to the press sheet – Overlay-type – Overlays add density to press sheet – Single-sheet type – Not all spot colors are available – May appear out-of-register – Colorants are NOT ink Single-Sheet Contract Proofs Press Contract-Proofs Each separate image is built on one base sheet The best proof Advantages – It not only resembles a press sheet, it is a press sheet – Available from many manufacturers Advantages – May appear on actual press stock – looks like a press sheet – Colorants may match ink color standards – Same exact stock as press run – No overlays to appear out-of-register or add density – Same inks as press run – May build-in press characteristics – Builds-in press variables such as dot gain and effects of water-in-ink. Disadvantages – Costly Disadvantages – Spot colors may not be available – Press is probably not the same as actual press run – Cannot be used as a progressive proof » May have different characteristics – Colorants are NOT ink – Very costly & time-consuming Page ‹#› Proofing Problems to Consider Color model employed by proofing system Screening technique (or lack of) Do the colorants used by system match ink colors? Available colors Prediction of press characteristics Does the proof demonstrate dot-gain? – If not, the proof will look lighter than the press sheet. Page ‹#›.