ImageMagick

ImageMagick® is to images as ffmpeg is to audio and video. It's the swiss army knife of image processing utilities - SIPS for Windows.

Because it's a command line utility, it can be scripted.

ImageMagick is free software delivered as a ready-to-run binary distribution or as source code that you may use, copy, modify, and distribute in both open and proprietary applications. It is distributed under a derived Apache 2.0 license.

ImageMagick utilizes multiple computational threads to increase performance and can read, process, or write mega-, giga-, or tera-pixel image sizes.

There are also builds for Android.

The authoritative source code repository is https://github.com/ImageMagick/ImageMagick.

Features and Capabilities

Animation create a GIF animation sequence from a group of images.
Bilateral blur non-linear, edge-preserving, and noise-reducing smoothing filter.
Color management accurate color management with color profiles or in lieu of-- built-in gamma compression or expansion as demanded by the colorspace.
Color thresholding force all pixels in the color range to white otherwise black.
Complex text layout bidirectional text support and shaping.
Composite overlap one image over another.
Connected component labeling uniquely label connected regions in an image.
Convex hull smallest area convex polygon containing the image foreground objects. In addition, the minimum bounding box and unrotate angle are also generated.
Decorate add a border or frame to an image.
Delineate image features Canny edge detection, Hough lines.
Discrete Fourier transform implements the forward and inverse DFT.
Distributed pixel cache offload intermediate pixel storage to one or more remote servers.
Draw add shapes or text to an image.
Encipher or decipher an image convert ordinary images into unintelligible gibberish and back again.
Format conversion convert an image from one format to another (e.g. PNG to JPEG).
Generalized pixel distortion correct for, or induce image distortions including perspective.
Heterogeneous distributed processing certain algorithms are OpenCL-enabled to take advantage of speed-ups offered by executing in concert across heterogeneous platforms consisting of CPUs, GPUs, and other processors.
High dynamic-range images accurately represent the wide range of intensity levels found in real scenes ranging from the brightest direct sunlight to the deepest darkest shadows.
Histogram equalization use adaptive histogram equalization to improve contrast in images.
Image cache secure methods and tools to cache images, image sequences, video, audio or metadata in a local folder..
Image calculator apply a mathematical expression to an image, image sequence, or image channels.
Image gradients create a gradual blend of two colors whose shape is horizontal, vertical, circular, or elliptical.
Image identification describe the format and attributes of an image.
Large image support read, process, or write mega-, giga-, or tera-pixel image sizes.
Montage juxtapose image thumbnails on an image canvas.
Morphology of shapes extract features, describe shapes, and recognize patterns in images.
Motion picture support read and write the common image formats used in digital film work.
Multispectral imagery support multispectral imagery up to 64 bands.
Noise and color reduction Kuwahara Filter, mean-shift.
Perceptual hash map visually identical images to the same or similar hash-- useful in image retrieval, authentication, indexing, or copy detection as well as digital watermarking.
Special effects blur, sharpen, threshold, or tint an image.
Text & comments insert descriptive or artistic text in an image.
Threads of execution support ImageMagick is thread safe and most internal algorithms execute in parallel to take advantage of speed-ups offered by multicore processor chips.
Transform resize, rotate, deskew, crop, flip or trim an image.
Transparency render portions of an image invisible.
Virtual pixel support convenient access to pixels outside the image boundaries.

Scripting Features
Command-line processing utilize ImageMagick from the command-line.
Examples of ImageMagick Usage Basic comand line usage
ImageMagick examples Basic scripting examples
Fred's ImageMagick Scripts Advanced scripting examples
Snibgo's ImageMagick Cookbook Advanced scripting examples
Script Porting Guide Porting old scripts