Computer Techniques

Digital Silk Screen Project ala Andy WarholAdapted from Water-Based Screen Printing

Today by Roni Henning

Using Photoshop• Use Photoshop to draw direct marks and

textures, create hard-edged shapes on separate layers, try different colors and work out composition. Use a digital photograph that you have taken and then modify it using tone controls, filters, and expanded painting tools. Apply special-effect filters to manipulate images and convert continuous-tone images to “line-art”, and other high-contrast graphic conversions like halftones, mezzotint-like random-dot dithers, or posterizations.

Save Your Work Often!• Save your work frequently as you progress to avoid losing anything in the event of

a computer freeze or power problem. Make duplicates of your images at important stages for later reference. One easy way to do this is to open the History Palette (got o Window>History) and click on the left, bottom>Create New Document from Current State icon. Save as a regular Photoshop file (psd) or TIFF (tif), but not as a JPEG (jpg). The JPEG file format does not save layers and channels and will lose information when frequently opened and closed.

Create New Document from current state

Adding New Images or New Windows

• When you scan in a photograph, or open a new window to work in, you need to set the resolution of the image. As reference, 72 ppi is coarse and 600ppi is much finer. The resolution you will set depends on what kind of art you are working with an how it will be printed.

• For simplicity, go ahead and click on Image>Image Size. Set the document size to the printing size you want (a full-size sheet of paper is 8.5 x 10 inches). Set the resolution to 200 (as seen above) and then save duplicate copies of your image so that you can experiment with posterizing, mezzotints, halftones, and dithers.

Converting Continuous Tone (Value) to Line

• “Line art” refers to all black, high-contrast art. There are a number of ways to change continuous-tone images to high contrast using tonal adjustments, filters, or bitmap mode. Sometimes combining more than one operation yields results with more detail than applying just one.

• Line Shot: A negative image, photographed from mechanical art, that is used for stripping or scanning.

• Making a Line Shot:– To simulate a copy camera “line shot,” use the

Threshold command to break the image down into only black and white with no continuous tones.

– Choose Image > Adjustments > Threshold

– Adjust the slider to change the distribution of white and black. Threshold abstracts the continuous image by pushing grays into either the white camp or black camp, resulting in a strong, high-contrast graphic image.

• There are a number of other ways to change an image toward a higher contrast that are not as radical as the Threshold command and will hold more detail as texture….

• Overlapping the Unsharp Mask Filter, sometimes sequentially to the image also gives great results.

Choose Filter > Sharpen > Unsharp Mask. Make sure the preview button is selected. Use your mouse to scroll through the image to find an area to review and compare pixels.

• Try applying the Mezotint Filter.

Filter > Pixelate > Mezzotint. This will convert the image to a random pattern of black and white areas. To use the filter choose a dot pattern.

• Experiment with other filters to explore developing more contrast within your image or to help your image be more expressive.

• Remember that if you do not like how the image changes, press control > Z and the image will revert back to its previous state.

Adjusting Tone• Brightness/Contrast is used for very simple

contrast adjustments by moving two sliders back and forth.

• Choose Image > Adjustments > Brightness/Contrast.

• However, when you need finer control, the Levels command is a more sensitive tool.

• Choose Image > Adjustments > Levels

• The input graph shows the distribution of black (left side) and white (right side) in an image. Space between the left triangle slider and the beginning of the black graph indicates a lack of 100 percent black, and the same goes for the right side with respect to pure white. To include pure black and white in the image, move the sliders inward until they touch the graph, and then adjust the middle (midtone slider). The more you move the sliders toward the center, the more grays you eliminate, creating higher contrast.

• However, if you want to maintain the illusion of photographic continuous tone, converting your fully-toned image to a diffusion dither or a halftone is a good graphic solution, and adjusting the original image to its highest contrast is not advantageous.

• Keep reading to learn how to dither….

Diffusion Dither

• A diffusion dither is an artistic looking random—dot halftone pattern that simulates continuous tone by placing small, irregular, mezzotint-like marks closer or farther apart. The size of the marks stays the same.

• Go to Image > Mode > Grayscale and click discard. Or, use Image > Adjustments > Black & White to convert to grayscale.

• Go to Image > Mode > Bitmap > Diffusion Dither. Set the output to 100 -150 Pixels.

• A good rule of thumb is: If the continuous-tone image looks good on the monitor, it will probably screenprint too dark and lose detail due to ink spread after conversion to dither or halftone. To compensate, go back to Choose Image > Adjustments > Levels and lighten blacks (left Output Levels slider) to create detail in the shadow areas prior to dithering. Try typing 25 to 35 in the left box (or manually moving the slider inward) to lighten black to a dark gray. Changing the right Output Levels from 255-245 would put small dots in the highlights so they don’t “pop”.

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Testing Your Image

• One simple test is to print your image on an inkjet printer using regular printing paper. Whether the detail fills in is an indication of what will happen when screen printing. If it looks “filled in,” undo the dither or halftone and lighten the blacks more. You may also need to lower the resolution to make the marks bigger (go back to image > mode > bitmap and reduce the resolution output).

• Note that after you apply a dither, what you see on the screen will usually look coarser than how your positive will print. Go to View > Actual Pixels to see a more accurate idea of what the marks in the dither will look like. If need be, undo and lighten the darks using Levels, and reapply the dither. Print a test onto your computer paper using an inkjet printer to see if it fills in.

Examples of gray scale, unsharp mask, and dithering in comparison to the regular photograph.

Examples of combined techniques using photoshop filters, grayscale, and bitmap techniques.

Changing Continuous Tone to Halftone (or getting rid of your gray shapes)

• Remember that all grays will translate to black on the silk screen. Therefore, in order to show areas that are to have the effect of grayscale – you will need to break that area down into pixels so that the silk screen has blocks and openings to allude to various shades.

• This is called half-tone.

• Magazines and newspapers use halftone dots to convert continuous-tone photographs into ink-printable form. The size of the dots and white spaces between them create the illusion of continuous tone. Again, an image that looks good on your monitor probably will print too dark, so when converting to a halftone, dither, or mezzotint, compensate by lightening the shadow areas and lowering the highlights slightly using the Levels Output box. An easy way to apply a large-dot halftone to a grayscale image is the with the Color Halftone Filter.

• Choose Filter > Pixelate > Color Halftone• Enter a value in pixels for the maximum radius of a

half-tone dot from 4 – 127.• Enter a screen angle dot – use 1 for grayscale images.

• Continue editing your image until you are satisfied that you have created a “Warhol” like photograph that creates value through pixelation rather than solid shapes.