Find the best free programs like GIMP for Mac. More than 14 alternatives to choose: Autodesk Pixlr, Photoscape X for Mac, Pinta and more. The newest update for GIMP gives a slew of new features and a glimpse into the future. Filters, effects and stickers for high quality photo editing.
Script-Fu - High Pass This is an adjustable script, high pass filters have a long and varied history, this one is a re-work of script by Rob Antonishen. His blog post describing the original filter is here: High Pass is often used as a sharpening tool, but it is a bit more at home in the quot;contrast' department. To ease its use as a sharpening tool, however, I include the 'overlay' option in the settings dialog. Here's a list of the different modes: Colour - I think this is the same as photoshop's high pass filter effect. Preserve DC - like colour, but adds the average image colour back in.
Greyscale - this desaturates the layer before high pass filtering. Greyscale, Apply Chroma - as above, but blends it in with the source layer colours Redrobes - (named after the technique described by Redrobes).