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Someone asked me how to make a step gradient to test paper/ink combinations. I figure this has broader topic than the thread it was in so I started this as a new one. There are actually a few different ways but this one is relatively numerically precise (but more tedious than some). 1. Create a new *CMYK* file that fits on the size paper you want to use for tests and a multiple of 10 for the resolution. I use 8 inches wide by 10 inches tall at a resolution of 100 pixels per inch (you could use metric measures also then the resolution would be perhaps 10 pixels per centimeter). 2. Determine how many steps you want in the gradient (if you are using it to set Photoshop's dot area curves you need 14 steps for a general purpose test you might want about 20). 3. Divide the length of your page by the number of steps to get the size of each step (subtract off any margins required including any area you might want to use for labeling). 4. Divide the width of the page by the number of columns you need (a single full set of inks need a minimum of four, if you want to add a note block next to each patch you need eight). 5. Set the marquis tool to the "Fixed Size" style and set it at the number of pixels that will give the size patch you want. For example if you want a patch that is one half inch by one half inch you would use 50 pixels by 50 pixels in the 100 pixel per inch resolution of the file. 6. Make a grid with the marquis tool by starting at the top of you first column and making a selection then stroke it (Edit/Stroke) at the number of pixels you want for a dividing line. Using the Shift/Down Arrow (which advances ten pixels at a time) continue down the page until you have a column then do as many columns as you need until you have a matrix waiting to be filled in with color (note, you may want to try this using stroked paths to make a matrix or do it in Illustrator but the marquis tool works okay as well) 7. Once you have the matrix start filling it with the paint bucket tool. Set the first color using the CMYK color picker to 100% Cyan, 0% everything else and fill the first matrix cell with that color. Fill second color with (say) 95% Cyan, 0% everything else, etc. If you were making a test sheet for Photoshop dot area curves the patches would be in the sequence 100%/90%/80%/70%/60%/50%/40%/30%/20%/10%/8%/6%/4%/2%. For a general test page you might just want to use multiples of 5% going from 100% to 5% in sequence. Do that *in CMYK color* for all the inks, C,M,Y, and K. 8. Add text to label the boxes if you left room for that and need it (for comparing spectrometer measurements on the printouts for example). And that is it for a CMYK test page. Any time you open this file if be sure you tell Photoshop not to convert it or color mange it (just say "no" to Photoshop). RGB test page - take the CMYK test page and convert it to multichannel mode then convert it to RGB mode. *Don't* convert directly from CMYK to RGB as this will scramble the pure ink colors. Resizing - if you didn't get the size just right and want to resize or want to increase the resolution be sure to use the Nearest Neighbor in the Image/Resize Image command. The other selection will make the nice sharp rectangular cell boarders softer. Multiple tests on a single sheet of paper - Resize the whole matrix page making it narrower and holding it to the left of the page on resizing. Copy the matrix to a new layer on the right side of the page. You can get two to four test layers depending on how narrow you squeeze the matrix. Turn off all the layers then turn a new one on each time you run the paper through the printer (remember to turn the last layer off or it will overprint the previous print). Alternate (simpler but less precise) methods - make four gradients using the gradient tool in columnar rectangular selections (one for each of the CMYK inks) with the foreground color set at 100% and the Background color set to white (0% CMYandK). Then Image/Adjust/Posterize the file selecting the number of steps you want in the gradients. This will make a pretty good set of step gradients for casual visual tests. You can also start in RGB instead of CMYK if you translate the CMYK color values into RGB terminology for the picker (ie 100% Cyan is 255 Green, 255% Blue, 0 Red). Don't try to specify CMYK colors in the picker when you are in an RGB document. The colors will not print correctly. Dan Culbertson - Turn off HTML mail features. Keep quoted material short. Use accurate subject lines. http://www.leben.com/lists for list instructions.
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