GIMP Plugins

Gimp Astronomy Plugins

These plug-ins for Gimp intend to be useful for astronomical image processing.

Some interesting plug-ins found on the internet:

Exposure Blend A plug-in to blend images with different exposure lengthes.
Fix CA Fixes chromatic abberation.
Purple Fringe Fix Reduces purple fringes around stars.

Plug-ins that I wrote (download below):

Set mode for all layers A simple batch script to set overlay mode to all layers.
Set brightness and contrast for all layers This script sets brightness and contrast to all layers; it doesn't provide a preview as the normal brightness & contrast plugin.
Normalize all layers Batch applies the normalize function (Layer->Colors->Automatic->Normlize) to all layers.
Subtract dark from each layer Subtracts a dark frame from all layers; naturally the dark frame should have the same size as all layers.
Divide all layers by a flat Divides all layers by a flat field; size issue as above.
Draw border with image information Draws a border (up to 2 different colors) around your images and on the bottom some information about your image, up to 2 lines at up to 3 positions (aligned left, right and centered) (See for example here).
Align layers This plug-in moves (and rotates) the layers that they overlap correctly. For alignment by center of disk / brightness, select the area, where the star is, that you want to user for alignment. For cross correlation alignment, select the object you want to use for selection (from the first layer). Optionally you can crop the image to the area, where the layers overlap. De-rotation is done by selecting a second star during alignment process.
Merge layers Merges all layers. You can choose, which method for the mean value you want: Arithmetic, geometric, median, sigma median (1 or 2 pass).
Sigma median is a median of all values inside [median-sigma;median+sigma] with sigma the standard deviation.
The pixel values are weighted by alpha value (for arithmetic and geometric mean value), and ignored (for all median mean values) if alpha channel is 0.
You can mulitply each pixel value by a given constant and then add a given constant (before calculating the mean value!).
A preview widget lets you decide which is the best method for you.
Background gradient Tries to create a layer containing the background for an artificial flat field.
The plug-in uses the following strategy: Loop through a number of areas (size as give by user), omitting invisible parts and calculate the median. Clip all values outside median +- n*sigma, where n is given by user. This might be done several times, as specified by user. Then a polynome of order 4 is fitted through these pivotal points, and the normalized values are written to the background gradient layer.
Use this plug-in in the following way: Copy the layer you want to work with, and cut out all areas with large objects, that are brighter than the background (nebulae, galaxies, ...). Then run the plug-in with appropriate values.
The result can be very good or also very poor, depending on the area of the cut object and the number of stars in the image. Images of the milky way obviously give bad results.
Background gradient batch script To batch normalize the background of all images in a folder.
Run on the command line something like
gimp -i -b '(background-gradient-batch "*.jpg" 200 200 2 1.0 200 0 0)' -b '(gimp-quit 0)' Parameters are: image list, box width, box height, numbers of iteration of sigma clipping, sigma, minimum number of values inside a box, weighted values (0=all values,1=darkest,2=brightest), percentage of darkest or brightest values
Artificial stars Creates an artificial star distribution.
The interface is splitted: On the right side, you can set up the options for the star distribution, on the right side how they will be drawn. To actually calculate a star distribution, you need to click on the button, as recalculation might take very long for many stars.
Changes on the left side only affect the preview.
The sample distribution buttons give you an idea, what you can do with this plug-in.
Artificial galaxies Creates an artificial galaxy.
Quite difficult to implement, only elliptical galaxies by now.
Star rounding Rounds longish stars (tracking errors...)

Download latest source:
MD5 sum: c8e3cbde46b7462f13703fe5cb2fcb04

Download latest windows binaries (built for Gimp 2.8 with Mingw):
MD5 sum: 8b9c2fd580c63edb1a468419d19b683f