For a long time I've watched the images/prints in newspapers and commercials thinking how it is actually printed, with just a four colors overlapping. Forming beautiful little patterns. Some time ago I started to read about the techniques used and got more and more interested about it. There are “newsprint”-filters in almost every image-manipulation software (including GIMP), but they are not very good; I guess they are aimed for people who actually design data for real CMYK-printing, not for people who just want to create nice looking effects still using the full color space (and -scale) like me.
I decided to implement the effect with different design-considerations, aiming it to be able to look smooth without VERY high resolutions. The program to be created should be able to “print” any image with as “real” halftone CMYK as possible, including “pressure”, “ink-bleeding” and other physical elements affecting when the image is done the actual (physical) printing. This is what my test turned out.
Processing of an image goes like this:
- Calculate a gray scale mask with selected type (dot, lines with different powers, square).
- Calculate the orientation matrices for each color-component with selected angels and size.
- Use attribute “sizediv” to downscale the image with as high quality as possible
- If enabled, convert the downscaled image into CMYK-color space.
- Create a target image with same dimensions with the source image
- Loop though each pixel of the target image
- Resample a color from downscaled CMYK(or RGBA) image.
- Apply contrast (“overcut”)
- Transform the current coordinate with pre-calculated matrices for each color component and get mask values from these positions.
- Apply noise to the mask values with selected noise-power and size.
- Calculate a delta vector from (sampled_color_from_downscaled_source – mask_values_for_each_component)
- Use attribute “pressure” as contrast for the deltavector.
- Targetcolor = 128 + final deltavector.
Software is made with Qt and tested on Windows 7 and Linux. The graphics processing is completely custom and does not deploy Qt on any other part than providing loaders/savers for the images.
I made couple of videos earlier if you want to see it in action. The first one is little older version with fewer controls, but it shows more the “dot” masks than the other.
What do you think?