Halftone Printing

Following the screen printing workshop, I continued experimenting with halftones. I want to eventually create a final piece that reflects inspiration from printers such as Andy Warhol and Roy Lichtenstein. I particularly like the larger dot sizes of both artists because they give the final image a hand-crafted look that separates it from the photographic process while still inferring its photographic roots.

Dot Pitch Size

I used an image from my portfolio as a test piece, chosen because it was high-resolution and included facial detail. Aron White suggests a resolution above 300ppi for the best results (White, 2022). The original image was converted to greyscale and adjusted to enhance the contrast.

I experimented with two halftone modes: Bitmap and Colour Halftone Filter. The first changes the native mode of the image from RGB, or Greyscale depending upon the source, to a black and white bitmap. The second option applies a halftone filter to the original RGB or Greyscale image. This second approach can be re-editable if the source layer is converted for smart filters.

I used three differing dot sizes for both bitmap and filter methods, adjusting the outputs to provide a variation in appearance. Because the size of the dot is not proportional to the size of the original image it was important to know the size of the photograph before the conversion to halftone. A much larger source image would require a different dot size in order to achieve the same aesthetic. I resized my source image to A4.

Bitmap Preparation

The Bitmap process is the most straightforward of the two processes. To convert an image file to a bitmap I used the Image>Mode>Bitmap option from the top menu. For this process to work the image needs to be converted to 8bit mode first. A setting box will appear during the conversion process, I chose a setting of 300dpi and an angle of 45 degrees (the default). I varied the Lines per inch (LPI) to 40, 57, and 100 LPI.

The results on the screen were:

Bitmap Test (on-screen)

Halftone Preparation

To create a halftone image using filters first the image is converted to greyscale. I used Image>Mode>Greyscale. On a duplicated layer I applied the filter>Pixelate>Colour Halftone.  Because this is a process that will mimic a colour halftone image (it does not separate primary colour layers for printing colour halftones) the dropdown setting box includes more variables. The channel angles that I used were 108, 162, 90, and  45 degrees. Because this is a monochrome image the angles for each colour channel are not critical but editing them still changes the look of the dots in the final image, and was worth experimenting with. The dot sizes are chosen using “max radius” which is measured in pixels. I chose radius sizes of 6,7 and 8 pixels.

The results on the screen were:

Halftone Filter Test (on-screen)

It was far easier to see the moiré effect caused by the angle used for the colour halftone filter than it was on the bitmap version. As mentioned earlier, changing the angles in the filter settings affects how the moiré looks.

Screen Printing

The two test images were printed onto acetate and applied as masks on a 90T screen.

I then printed multiple copies onto a variety of paper to learn how the underlying paper affected the prints.

Some of the results are shown below.

From the results of this experiment, I preferred the larger dot sizes, 8PPI  prints using the filter method and 40LPI bitmap files. The bitmap images appeared cleaner than the halftone filter variants, but the filter produced a more spherical dot than the bitmap. There was also more control with the filter.

The next experiment will be to print full A3-sized images using the Halftone Filter process.

WHITE, A., 2022. Halftoning 101: How to Halftone Images in Photoshop [Viewed 10/11/2024]. Available from: https://www.shutterstock.com/blog/how-to-halftone-images-in-adobe-photoshop