Getting an Image on a photopolymer plate
The artwork to be made into a printed image must be made on transparent film such as an overhead projector slide (clear acetate sheet) drawn or printed in high contrast black and white or greyscale.
The artwork can start life as a photograph, but needs to be turned into a high contrast black and white image in order to make a successful photopolymer plate image. This can be achieved in a graphic package such as Photoshop tweaking the image adjustment controls for brightness, contrast etc. I found that the DxO Nik package of filters makes life much easier using the Silver Efx filters. It has many presets that can be fine tuned to give an outstanding quality to the image.
However . . .
In order for the plate to be able to hold onto the ink when colour from the lights tint through to full intensity tiny intaglio like indentations need to be created on the plate in much the same way as aquatint is used on metal plates. This is achieved by first exposing the plate under UV light with a stochastic mask (also known as an aquatint screen) The word stochastic means totally random and unpredictable - so basically a very random pattern of dots - invisible to the naked eye as they can be around 40 microns across (0.04 mm)
After the photopolymer plate has been exposed to UV light through the aquatint mask it is time to use the artwork transparency.