black and white

Maximize Local Contrast

Roy Johnson — Wed, 01 Jul 2009 18:36:27 +0200

FX-Foundry/Photo/Enhancement/Maximize Local Contrast... Like Stretch Contrast, but instead of using the minimum and maximum pixel values from the entire image, uses the minimum and maximum in the vicinity of a pixel to compute its new value. Takes a while to run, but really brings out textures. Result is a Grain Merge layer that adjusts values of the original image.

This filter operates on the visible image, not on a layer or selection.

Radius indicates how wide a pixel's influence is. If you choose too small a value, adjustment will be too localized and the image will look patchy. Larger values take a bit longer to run.

Threshold indicates how many neighboring gray values above and below a value can be treated as the same, in finding minimum and maximum values. Purely a speed trade-off. Using very low values will make it very slow. Too high values will cause visible "steps" in color values. The latest version does not include threshold, but the older version is still available.

"Feather Haloes" helps smooth out haloes around high-contrast areas.

"Keep Min and Max Layers" leaves the intermediate layers in the stack so you can look at them if you're interested.

Update (21 Jul 2009):

New algorithm that works right without any compromises for speed. No scaling, no threshold. It does take a bit of time on large images; 45 seconds for a 1500x2000 pixel image on a modern but not especially powerful PC. The full 8-megapixel image took about 3 minutes. Most of the time is spent on grow-selection, so don't be alarmed when the progress meter seems to hang up for a while. There are just two grows and two feathers to do.
If you want a speed compromise, I've added Scaledown factor, which will reduce the time spent in selection a lot, but will add some time for scaling the image. There's essentially no loss of quality. Recommended for especially large images.

Updates (13 Jul 2009):

SPEED! Mapping of Min and Max is done on scaled-down layers. Now even large images can be done in reasonable time.
Feather haloes feature for more reasonable results on high-contrast images and images with big flat areas
Layer mask keeps narrow-contrast areas under control

Updates (9 Jul 2009):

Fixed the bug that left strange artifacts in the image.
Changed radius to work as a % of image size (maximum dimension)
Increased feathering and added limits to min and max layers to control haloes around small, high-contrast features
Got rid of sample images. Will find better examples.

gimp-netpbm2gimp-plugins and Netpbm2Gimp

pakin — Sat, 28 Feb 2009 04:01:55 +0100

gimp-netpbm2gimp-plugins is a collection of over 200 GIMP plug-ins produced by running the source code of the Netpbm graphics filters through Netpbm2Gimp, which is described below. (Note: Think "GIMP" where the Netpbm graphics filter documentation says "PBM", "PGM", "PPM", "PNM", or "PAM".) There is a particular emphasis on load/save plug-ins for obscure graphics formats, but a number of miscellaneous and useful image filters and image generators are included as well.

Netpbm2Gimp is a tool for programmers that converts programs written using the easy-to-use Netpbm library into GIMP plug-ins. Netpbm2Gimp reimplements the Netpbm functions in terms of GIMP/GTK+ functions, thereby hiding much of the complexity of plug-in development. With Netpbm2Gimp, plug-in developers needn't worry about registering plug-ins with the GIMP core, displaying dialog boxes to request input from the user, displaying dialog boxes to present the user with status or error information, handling noninteractive usage (for the GIMP scripting interfaces), managing various GIMP data structures (images, layers, drawables, shadow buffers, the tile cache, etc.), updating the progress bar, controlling the undo stack, and performing the various other operations that are needed in the context of a graphical user interface. All of those features are handled automatically by Netpbm2Gimp.

The source code and Linux binaries for both Netpbm2Gimp and gimp-netpbm2gimp-plugins are available from the Netpbm2Gimp home page, http://netpbm2gimp.sourceforge.net/.

Film Grain

manutd101 — Sun, 26 Oct 2008 18:56:35 +0100

This script adds a realistic film grain effect to a black and white or toned image. To install, copy the attached file to GIMP/share/gimp/2.0/scripts. The larger the file you are running it on, the larger the value you should have for Strength. The value for Sharpness depends on your preferences, but I usually start at 1 and go from there. The lower the value, the sharper the noise.

BW Labs

baruchel — Sat, 21 Jun 2008 22:28:21 +0200

This is another script for converting a picture to black & white. The decompose plugin must to be available. The way of converting the picture is rather different than what other plugins do. Two different luminance layers are mixed according to a mask made with a saturation layer. Six different combinations are provided. Functions are available under the menu script-fu/Photography/BW Labs.

Color to B&W by Gradient

JimSabatke — Thu, 07 Feb 2008 06:17:11 +0100

A set of gradients for toning B&W photos. New are multi-colored toning gradients (thanks Ron Antonishen for the conversion script), and 3 Albubum print gradients. Instructions for use are in the README file.

Note: you will generally get better results from:

->color->map->sample colorize

than from

->color->map->gradient map