How to convert gradients to lpi for screen printing

Written by blake ruby
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How to convert gradients to lpi for screen printing
A photograph must be converted to a dot pattern for screen printing. (Stockbyte/Stockbyte/Getty Images)

If you want to print a photograph or illustration containing gradients, or smooth tones, onto a T-shirt or other object, you must convert the image to a "halftone." This is an image made up of dots measured in lines per inch (LPI). LPI refers to the space between the dots in one inch of a halftone image. Adobe Photoshop, a graphics software program, is the industry standard for creating halftone images. However, the GNU Image Manipulation Program (GIMP) is a free, open-source alternative with many Photoshop-like features. Once you have converted the image, you can take it to a screen printing company to have it printed.

Skill level:
Moderately Challenging


  1. 1

    Check the image size and resolution. For example, in GIMP, select "Scale Image" from the Image menu. This brings up a dialogue box displaying the dimensions and resolution of the image. For successful screen printing, your image should be the width it will appear on the final product and have a resolution of 150 to 300 pixels per inch (PPI).

  2. 2

    Convert your colour image to grayscale. If you will be printing with just one ink colour, change your entire image to grayscale. In Photoshop's Image menu, select "Mode: Grayscale." If you will be printing a multicolour image, you will need to do this for each colour of ink you plan to use.

  3. 3

    Convert the grayscale image to a halftone. For example, in Photoshop's Image menu, choose "Mode: Bitmap" and select "Halftone Screen." Input your desired LPI number, or how coarse to make the line screen. If you are printing on an absorbent surface like a T-shirt, use a coarser halftone screen of 35 to 65 LPI. If you are printing on a smooth surface, you may be able to use a finer screen, or higher LPI number.

  4. 4

    Check your final image. Don't rely on your monitor--print out your screen-ready image with a high-quality laser printer if possible, and look at it both close up and from a distance. Make sure there's no "moire," or interference, pattern.

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