Halftone prints can be used to create stencils for screen printing (see our previous post Screen Printing with Diazo Photo Emulsion).
Halftone is a reprographic technique which simulates greyscale imagery. It does this by using black dots in different sizes set at varying distances to each other. A halftone image can be printed onto a clear acetate sheet, placed on a screen treated with Diazo Photo Emulsion and exposed to a bright light source. The light sets the exposed areas of photo emulsion onto the screen, while the covered area remains soft and can be washed away to create the stencil.
A halftone image can be drawn by hand but if you’re lucky enough to have a copy of Photoshop, you can transform images using the ‘Image > Mode’ option.
Adobe Photoshop CS3 was used to create the halftone image above. The ‘dots’ are actually squares. Photoshop provides a number of choices for the dot shapes as well as the angle at which they are presented.
Choose an image with either no background or a light coloured background and open it in Photoshop.
I chose a photograph I took of Ruth who worked for George Weil for 11 years as our bookkeeper until she retired last year.
I first turned it into a greyscale image (choose ‘Image > Greyscale’ and discard the colour information) and then increased the brightness and contrast (choose ‘Image > Adjustments > Brightness/Contrast) until the background became white. If there are any marks in the background, use the Eraser tool to wipe them out.
Next you need to change the image to a bitmap (choose ‘Image > Bitmap’ and select halftone screen from ‘Method’. The halftone screen options give you the chance to experiment. Play around with the frequency, angle and shape until you are happy with the effect).