Secrets of Scanning Color on Black and White Scanners P.O.Box 958 New York, NY 10024-0541 FAX: 212 874-0578 E-Mail: Pink.Soda@tbr.com Copyright 1994, Pink Soda, Inc., all rights reserved. This article may be distributed electronically or in print form as long as no fee is charged for distribution. All other rights including publication in books, magazines,or collections etc. whether electronic and print media are reserved by Pink Soda, Inc. ------------------- Summary: Part One 1 presents the theory behind doing color scanning on a black and white scanner. Part TWO 2 gives detailed instructions on using PhotoShop, PhotoStyler, and other image processing software. ------------------- Part ONE I. What Is Color? To a human being color is the deep red of a rose, the verdant green of a springtime forest, the pink of a child's cheek. Color is emotion--color is life. To a computer or scanner, there is no such thing as color. There is only pixel intensity. Color is a subjective and biological response. Computer color is fakery, a trick of pixel stimulation that creates the illusion of color. On a color display there are 3 planes or channels of pixels: red, green, and blue. Combinations of just these 3 colors can recreate all the colors of the rainbow and more. A scanner--black and white or color--does not "see" color, it "sees" only intensity commonly in the 256 intensity range. 0 intensity equals black or no value for a particularly color channel, and intensity 255 = white or a 100% value of a certain color. In displaying an image, a monitor stimulates a red pixel 100% for all red and 0% for no red, and the 254 other ranges in between. Doing this for 3 channels, therefore allows a monitor to display or trick the eye into seeing up to 16 million colors, i.e., 256 to the 3rd power or 256 X 256 X 256. II. A black and white scanner is a color scanner. Scanning in grayscale is actually scanning in one range of intensity which can be thought of as one color channel. If you convert a grayscale image to a color image and look at the histogram, you will see that the grayscale values are always of equal intensity in each of the RGB channels. That is a gray value of say 128 is represented on a color monitor as a Red value of 128, a Green value of 128 and a Blue value of 128. Since a black and white scanner scans 1 channel, the logical conclusion is that if you map this channel to either Red or Green or Blue you will get a single channel of one of the RGB colors. For example, converting a grayscale image to color produces a color image in which all the values for RGB are equal, and the image looks exactly the same on the monitor. However, if you remove the Green and Blue components of this image, you will then see the image in monochrome red. [view dcolor.gif] The basic trick to scanning color on a black and white scanner then, is to scan the same image 3 times and tell the computer that they are respectively the red, green, and blue. Of course, unless each of the scans covers a different range of intensities and those intensities correspond in some way to the red, green, and blue components of the original image, you still end up with a grayscale image. II. Try this at home. All it takes to scan 3 different intensities is transparent plastic. To scan red, green, and blue, pieces of red, green, and blue plastic are put between the image and the scanbed and the resulting scans then contain only those components of the image. The closer that these pieces of plastic correspond to what a computer registers as red, green, and blue, the closer the image created will be to the original. Once the 3 scans are done, they can be merged as separate channels into a single color image in PhotoShop, PhotoStyler or in a utility such Presto! Color. III. Calibrating the Color Image. Since the scans are done on a so-called black and white scanner, there is no inherent routine that equalizes the values of each of the channels, as there is in a color scanner. We must somehow tell the computer that it is to ÍdisplayÎ a complete range of intensities for each channel. This is achieved through a process called linearizatiion or contrast stretching. The 3 scans, which we can now refer to as our RGB channels can be linearized before merging or after merging. The important thing is that each channel be linearized individually. Different software programs, a number of which are detailed in the boxes accompanying this article, will produce different results if you merge the channesl first and then linearize or linearize first and then merge. Photoshop and PhotoStyler are particularly useful for this because the values can be saved as curves and reapplied to other images. IV. Good Color/Bad Color The single most important factor in using this technique for color scanning is the original RGB filters--the pieces of transparent plastic used in the scans. While some of the imbalance that may result with using "unbalanced" filters can be compensated for within the image processing software, the closer the original filters are to what a computer "sees" as red, green, and blue, the better the quality of the color image produced. (You can obtain professional, color- balanced filters *8"x 10") by sending $14.95 + $2.00 (S&H) to Pink Soda (VISA/MC/AMEX accepted) or credit card order by FAX.) As you can see from the samples images shown here, with the right filters, the results can equal that of a desktop color scanner. The output can be imported into multi-media and business presentation programs as well as printed on color printers such as the Fargo Primera, HP Deskjet, QMS and others. [view fishpc.gif] ----------------- Boxed Text Head: Scanning Black and White for Color Doing the Filtered Scans Obtain 3 pieces of transparent colored plastic: red, green, and blue. The best place to look is your local art supply store or order professional, color balanced filters from Pink Soda. Place the image on the scanbed and do a preview scan. It's a good idea to lightly tape the image (not the filter) to the side of the scanbed so that it does not move during the scanning process. Crop the image but DO NOT ADJUST ANY VALUES, keep the contrast, brightness and other controls at their default settings. Slip the red piece of plastic between the image and the scanbed and do the first scan. Do the same for the green and blue filters. IMPORTANT: It is very important that each of the three scans be exactly the same size and carried out at the same scanner settings for dpi, brightness contrast etc. NOTE: the three scans may look virtually black. That's okay. If the results are not good, e.g., if your final merged image is very dark and lacking in color values make a modest adjustment to the brightness value during the scan process. Increase the brightness by 5%-10% (small increases produce large differences). BE SURE TO USE THE SMAE SETTING FOR ALL 3 SCAN PASSES. Merging and Linearizing in PhotoShop 2.x (MAC or Windows) 1. Open all three images--they will probably look very very dark on your screen. Under the menu item WINDOW, SHOW CHANNELS select MERGE CHANNELS by RGB. Make sure that you indicate the correct name for each of the scans. 2. Adjust image. Select menu item, IMAGE, ADJUST, CURVES. Select Red, Green, and Blue channels individually. For EACH channel press the Auto Contrast Adjust button (it looks like a half black/half white circle.) 3. Adjust the gamma. You should now have a fairly decent color image that will be somehwat dark and missing details. To compensate for this select the menu item IMAGE-- ADJUST--LEVELS filter to adjust the mid-ranges. This will bump up the details. Using PhotoStyler 1. Calibrate the filters. Unlike PhotoShop, PhotoStyler's auto adjust feature does not work well enough for this purpose. The RGB filters must be initially calibrated and a default curve created. Once the curve is created, it can be saved and applied to future images. To calibrate a default curve, scan a small section of each filter, 100 dpi x 100 dpi (yes, just the filter against a white background.) Open these and use the eyedropper to obtain the most common gray value in each. It may be a very dark gray value. Under the Menu Item IMAGE, COMBINE RGB TRUE COLOR BY, select RGB channels (make sure to indicate the correct name for each channel). Under the menu item IMAGE GRAY COLOR MAP, individually adjust the curve for each color channel so that all values above the noted value are mapped to 255 (it will be a steep straight line). SAVE THIS CURVE. 2. Do a 3 pass scan of a color image following the instructions given above. Merge the channels to create 1 color image and apply the saved curve. 3. Adjust the Gamma. I have found that adjusting the GAMMA value from the menu item IMAGE--GRAY/COLOR CORRECTION or IMAGE--GRAY/COLOR MAP will bump up the details nicely. ------------------------- Othe Programs Using Corel PhotoPaint!, Paintbrush, PaintShop Pro and other programs that do not have channel merging capabilities. Not all programs, for example CorelPaint! and the popular shareware program PaintShop Pro, have channel merging capabilities. Presto! Color is a utility that provides channel merging and color balancing capability. Presto! Color takes 3 same size black and white scans and converts each to a color channel, merges the channels, and outputs a 24 bit and or 8 bit color image file. Presto! Color creates a finished color image that can be edited, if desired, in any image processing program. Presto! Color is a DOS program. Mac users can run it in a DOS partition using software such as Soft PC. A Shareware version of Presto! Color has been uploaded to Compuserve, America On Line, and other BBSs. To order from Pink Soda, send $34.95 + $2.50 (S&H). Filters only are $14.95 (+$1 S&H). MONEY BACK GUARANTEE. Not recommended for hand scanners. A set of professional, color balanced RGB filters is included with the program. PrestoColor! carries out the entire process of channel merging, image linearization, and gamma correction. PrestoColor! is easier to use because calibration and linearization are automatic and the final image requires little if any retouching. This is particularly useful for users with little image processing skill available. In fact an image processing program is not even required. About the Author Ray Fournier is president of Pink Soda, Inc., a consulting firm located in New York City. Pink Soda has assisted small and large graphic design and advertising agencies such as McCaffrey & McCall and Young & Rubicam. Recently Pink Soda, in association with WMT Associates of New Jersey, designed and implemented the electronic publishing network for Bloomingdale's newspaper advertising department. How to Obtain a Copy of PrestoColor! Readers can obtain a copy of Presto! Color shareware version on CompuServe, America On Line, and other BBS services (PRESTOC.ZIP, keyword: scan). A more robust working demo with 4" x 4" filters can be obtained for $10 + $1 S&H from Pink Soda (applicable to purchase). PrestoColor! is available for $34.95 (+$2.50 S&H) and includes a set of professional color-balanced (8"x 10") RGB filters. (Money Back Guarantee. Visa/MC/Amex are accepted. NY State residents must addd 8.25% sales tax. Credit card orders by mail or FAX must include voice telephone number for verification. Please note disk size.) For more information or to order, write Pink Soda, Inc., P.O. Box 958, New York, NY 10024- 0541. Telephone 212 874-3581, FAX: 212 874-0578, e-mail Pink.Soda@tbr.com.