Printing Digital Images

Two Ways to Obtain Prints Print them yourself Use a printing service –Local –Online

Doing Your Own Prints Three type of printers available –Inkjet –Color Laser –Dye Sublimation

How Color Images Are Printed Color printers create images by dividing a page into thousands, or even millions, of tiny dots, each of which can be addressed by the computer. As the printer moves across and down the page, it can print a dot of color, print two or three colors on top of each other, or leave the spot blank (white).

The Two Basic System for Creating Color The two basic system for creating color are –additive –Subtractive Additive color is used by color displays to create the images you see. Additive color uses red, green and blue added together in various amounts to create all of the colors

Additive Color Additive color is used by color displays to create the images you see. Additive color uses red, green and blue to create color images on the screen.

Subtractive Color Color printers use the subtractive color system The primary subtractive colors are cyan, magenta, and yellow. By using one or more of the subtractive primaries on a dot eight different colors can be produced.

Colors from Subtractive Primaries Color 1Color 2Color 3Combined White CyanNone Cyan MagentaNone Magenta YellowNone Yellow CyanMagentaNoneBlue CyanYellowNoneGreen MagentaYellowNoneRed CyanMagentaYellowBlack

A black ink is added to the subtractive printing system. This provide a deeper black then can be created by the combination of cyan, magenta and yellow alone The name for this color system is CYMK, K being the black component.

Halftones and Dithers On most printers (dye-sub is an exception), each printed dot has the same density of color. If the printer only combined these solid colors, it would be limited to the eight primary colors for reproduction. To get the millions of colors in a photograph, the printer has to "fake" the colors by generating a pattern of small dots that the eye blends to form the desired shade.

This process is called halftoning or dithering and is controlled by the printers software. designing printer software that does halftoning well is as much art as it is science.

Halftoning is done by arranging the printable dots into grid-like groups, called cells then using these larger cells as a single unit to print pixels with Each cell may be 5 by 5 or 8 by 8 dots in size. The primary colors are combined in a pattern of dots in these cells, and the eye perceives them as intermediate hues.

For example, to print purple the printer uses a combination of magenta and cyan dots. For less saturated hues, the printer leaves some dots unprinted and hence white in color.

Inkjet Printers There are two types of inkjet printers that can print photographs The standard inkjet printer that uses four inks, cyan, magenta, yellow and black Photo inkjet printers that can have seven or more inks including cyan, light cyan, magenta, light magenta, yellow and black.

Part of an Inkjet Printer Print Head Assembly Print head - The core of an inkjet printer, the print head contains a series of nozzles that are used to spray drops of ink.

Ink cartridges - Depending on the manufacturer and model of the printer, ink cartridges come in various combinations, such as separate black and color cartridges, color and black in a single cartridge or even a cartridge for each ink color. The cartridges of some inkjet printers include the print head itself.

Print head stepper motor A stepper motor moves the print head assembly (print head and ink cartridges) back and forth across the paper.

Paper Feed Assembly Paper tray/feeder - Most inkjet printers have a tray that you load the paper into.

Rollers - A set of rollers pull the paper in from the tray or feeder and advance the paper when the print head assembly is ready for another pass. Paper feed stepper motor - This stepper motor powers the rollers to move the paper in the exact increment needed to ensure a continuous image is printed.

Control Circuitry A small but sophisticated amount of circuitry is built into the printer to control all the mechanical aspects of operation, as well as decode the information sent to the printer from the computer.

Printer Quality Determined by the dots per inch that can be printed by the print head. Also depends on how many tones or colors can be generated in each cell

How Droplets Are Created Link to flash movie

Color Laser Printers Are more expensive the Inkjet printers Supplies are more expensive The quality of photos approach the quality of a good photo inkjet printer Have a problem producing glossy prints.

Dye Sublimation Printers Where picture quality is very important, dye-sublimation printers are best. The "dye" in the name comes from the fact that the process uses solid dyes instead of inks or toner Sublimation" is the scientific term for a process where solids (in this case dyes) dyes are converted into a gas without going through an intervening liquid phase.

Materials Dye sub printers have their colored dyes in a transfer roll or ribbon. This roll contains consecutive page-sized panels of cyan, magenta, yellow and black dye. These printers require special paper that's designed to absorb the vaporous dye on contact

How it Works During printing, separate passes are made across the print for each of the four colors—cyan, magenta, yellow, and black. A thermal print head, consisting of thousands of heating elements, contacts the media being printed on and vaporizes the solid dyes.

What makes these printers unique is that the heating elements on print head can be set to any one of 256 temperatures. The hotter the temperature, the more dye is transferred to the paper. This precise control of the amount of dye that's vaporized controls the density or intensity of the resulting dot on the paper and produces continuous-tone images.

Because the dyes are transparent, a cyan dot may be printed on top of a magenta dot to make a blue dot. By varying the amount of C, Y, and M, any color within the printer's color range may be produced. Because they can vary the density of each color, dye-sub printers are the only ones that don't have to use halftoning or dithering to create a wide range of colors

Printing Your Own Pictures VS Printing Services Printing your own pictures advantages –Quicker turnaround –Control over result Printing your own pictures disadvantages –Cost –Convince

Photo Service Advantages –Cost –Ease of printing –Size of prints Photo Service Disadvantages –Instant gratification –Control