On 2014-07-12, 14:58, Pol Stra wrote:
I wonder, what can I do to reduce the size of those files while keeping a printable quality document?
Besides reducing the resolution, you can reduce the number of colours used in a PNG picture, which is called colour quantization. For example, we can differentiate between ca. 12 levels of gray (between black and white) with our eyes. So it is useless to differentiate between hundreds of different colours in a gray picture. I quantize all my gray pictures to use 12 colours only, and the difference is usually not visible, but it leads to a much smaller file size. For coloured pictures, you need of course more different colours, you have to try different values with each picture to find the best number. I use the tool pngnq for quantization. After quantization, one can further losslessy compress an image by removing unnecessary meta informations from the file, which can be done automatically with the tool Trimage. I've got both pngnq and Trimage from the repositories of my Linux distribution. Kind regards, Joshua