A document that details the GIMP's history can be found here:
The development plan for the future was outlined in the following message:
Throughout the lecture I will turn to the audience and ask them to come up with the algorithms that are used behind the scenes.
Those that have technical knowledge in image processing, please don't answer.
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A GIMP image is composed of layers. They can be viewed and manipulated using the Layers Dialog (
). These layers can be duplicated , deleted moved, etc.Every layer contains a special layer called the "alpha layer" that specifies its opacity. This layer is treated as a black and white bitmap that can be manipulated with all the normal tools, and in which black is considered full transparency (zero opacity) and white is full opacity between this layer and the layer below it.
The Resultant pixel of the two layers is calculated using the formula:
Result = (1-alpha) * PixelBelow + alpha * PixelAbove
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We can also use gradients as layer masks to create all kinds of fading effects.
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NoteMy partner for "Image Processing and Analysis" and I worked for quite some time to create a similar effect in Matlab.
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Most filters affect only the active layer, so if you wish them to have a cumulative effect on a combination of layers you'll need to merge them first (
or )Layers can be merged using other methods than their Alpha. These are available in the "Mode" combo-box of the layers dialog.
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The operations that are used to merge the various layers are described the in the Gimp User's Manual.
Look-up Tables (or LUT for short) are transformations that act on every pixel based on its value alone and not on the values of neighbouring pixels.
How can we increase/decrease the brightness and contrast of an image?
Increasing or decreasing the brightness involves adding or subtracting a certain amount from the value of each pixel.
The contrast can be increased by plotting an y=mx graph according to the value, where m is greater than 1 to increase the contrast, and less than 1 to decrease it.
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How can we brighten or darken an image without causing colour values to overflow?
If we assume that the maximal colour value is 1 and the minimal is 0, then by applying a function of x ** (1/gamma) to every pixel we will modify the histogram while not overflowing from the image boundaries (which cannot be said on brightness and contrast manipulations).
The more positive the Gamma is the brighter the resultant image will be.
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The "Equalize" operation constructs an appropriate Look-Up Table so that the histogram of the resultant image will be more or less a constant function.
Low colour values will remain lower than higher ones, but the spread of them will change.
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So far we have seen LUTs from the V value to the V value. But there can also be RGB to RGB LUTs. An example of it is the Color Map Rotation which enables us to swap a range of colours with other colours in the Hue spectrum.
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Another Useful LUT is the Color Balance. It enables one to increase or decrease the individual components of Red, Green and Blue for either shadows, midtones or highlights.
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There are more LUTs present in the GIMP. And if that's not enough you may wish to play with the Gimp::Pixel PDL bindings. (which is the GIMP's answer to the Image Toolbox of Matlab).
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:-)
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/usr/share/gimp/1.2/scripts/bovinated-logo.scm
.http://www.gimp.org/ - The GIMP's Homepage. Contains a lot of material and links.
http://gug.sunsite.dk/ - The GIMP Users' Group.
http://manual.gimp.org/ - The Gimp User's Manual. A complete book that covers GIMP 1.0.x with some plug-ins that as of then, were not distributed with it. Still Pertinent as it is very detailed and explains a lot of good techniques.
http://gimp-savvy.com/BOOK/ - "Grokking the GIMP" by Carey Bunks. This book aims to explain the "10% of the tools that are used 90% of the time." I did not read it thoroughly but it looks very nice.
http://www.xach.com/gimp/books/ - Xach's GIMP Books List. Lists, Reviews and links to other books, some of them available only in paper.
http://www.gimp.org/win32/ - GIMP for "the other" operating system which is sold by a large Redmond-based company. (All right - it's GIMP for Win32).
http://www.macgimp.org/ - MacGIMP - Gimp for Mac OS X.
http://www.gtk.org/ - The Homepage of the Gtk+ Toolkit which is the GUI toolkit used by the GIMP
RFC - The Future of the GIMP - This document explains the purpose of the 1.3.x and 1.9.x branches, and what is the workplan for the next releases of the GIMP.
http://www.gegl.org/ - The GIMP 'E' Graphics Library. A sophisticated image representation C library that will be used as the basis for GIMP 2.0.
The Lena Image (Yahoo) - contains links to information about the neophyte picture that became a standard in the image processing world.
The images used for this lecture can be found in this lecture images directory. This page is meant to detail their origins and their copyright notices.
This image is available from this page:
http://www.eso.org/~ndevilla/lena.html - The Lena Story
It is part of a Playboy centerfold and copyrighted by Playboy corporation. The latter, however has given permission to use this particular portion freely for image processing research.
The image there is available in GIF format, but I converted it to PNG.
I found this image here:
It seems to be the colour original of the Grayscale one. Usually, the grayscale one is used for image processing research (probably because scientific journals are usually not printed in colour), but I decided to use the colour version here as well.
These images were found on the image archive of Gimp-Savvy:
http://gimp-savvy.com/PHOTO-ARCHIVE/
It is copyright-free, so you can do with it as you please.
This is a photograph of Gabrielle Anwar, which can be found here:
http://www.candy-fans.com/anwar/index.html
It looks like it was scanned from a magazine, so it's almost surely copyrighted. However, distribution of copyrighted images on the Internet is so common, that I don't think one has anything to afraid of by using this image. Publishing it is a different story, though.
These images are part of the Propaganda collection of desktop backgrounds.
They are distributed under the GNU General Public License (GPL), which I'm not sure if makes too much sense for images. They were created using the GIMP, but the scripts or the temporary images used to create them are not available as far as I know.