Contact the authors Jun.Furuse@inria.fr and Pierre.Weis@inria.fr.
Created the 7th of February 2000.
Last update on Fri Oct 1 2004.

CamlImages

Version 2.2

Objective Caml image processing library

Note: this library is currently(=always) under development.

0. What is CamlImages ?

CamlImages is an image processing library, which provides

Basic functions for image processing and loading/saving various image file formats (hence providing a translation facility from format to format),
An interface with the Caml graphics library allows to display images in the Graphics module screen and to mix them with Caml drawings,
A freetype interface, integrated into the library: you can draw texts into images using any truetype fonts.

In addition, the library can handle huge images that cannot be (or can hardly be) stored into the main memory (the library then automatically creates swap files and escapes them to reduce the memory usage).

Additional example programs are supplied in the examples directory of the library:

converter:: a convertion program, that converts image from formats to formats.
crop:: a ``cropping'' program, that cuts an image to its edges.
edgedetect:: a program to detect edges into an image.
gifanim:: an animation program for gif encoded series of images.
liv:: an extension of the Unix ls command to view a set of images. (Also considered as a light version of xv with nice slide show capabilities.)
monochrome:: converts a color image to monochrome.
normalize:: normalizes the colormap of an image. This program anlyzes the colormap information of the image to normalize its brightness over the full range available.
resize:: a program to resize an image.
tiffps:: a program to output a postscript version of a tiff image (for instance to print it).
ttfimg:: true type font dump program. It can be used to create fancy banners or buttons.
Try for instance ttfimg ../../test/micap.ttf -message Bonjour -fg red -bg black. Visualize with liv (of course). ttfimg also creates some sample images of true type fonts. Try ttfimg -o sample_micap.jpg ../../test/micap.ttf.

1. Installation

Get the source tar ball, decompress it, and read the file INSTALL.
You can also access the read-only CVS repository which contains the latest developing (but not yet released) version.

2. Using CamlImages

2.1 Color models

CamlImages supports the following color models:

Rgb24: 24bit depth full color image.
Index8: 8bit depth indexed image with transparent information.
Index16: 16bit depth indexed image with transparent.
Rgba32: 32bit depth full color image, with the alpha channel.
Cmyk32: 32bit Cyan Magenta Yellow and blacK image. (Unfortunatelly, beautiful conversion between RGB and CMYK is not supported.)

For each color model, a corresponding module is provided. For example, use the module Rgb24 if you want to access 24bit depth full color images.

2.2 Load/Save image files and other fancy features

CamlImages supports loading and saving of the following file formats:

Bitmap, windows bitmap format (.bmp).
Gif, graphics interchange format (.gif) (not recommended).
Jpeg, joint photographic experts group (.jpeg or .jpg).
Png, portable network graphics (.png).
Tiff, tagged image file format (.tiff or .tif). (Color only.)
X pixmaps (.xpm). (Loading only.)
Encapsulated Postscript (using ghostscript)
xv thumbnail files (see xvthumb directory).

For each image format, we provide a separate module. For instance, use the Tiff module to load and save images stored in the tiff file format.
If you do not want to specify the file format, you can use Image.load: this function automatically analyses the header of the image file at hand and loads the image into the memory, if the library supports this format.

CamlImages also provides an interface to the internal image format of O'Caml's Graphics library (this way you can draw your image files into the Graphics window).

You can also draw strings on images using the Freetype library, which is an external library to load and render TrueType fonts.

2.3 Class interface

The modules with names beginning with the letter 'o' contains the object class interface for CamlImages.

2.4 Image swap

When you create/load a huge image, the computer memory may not be sufficient to contain all the data. (For example, this may happen if you are working with a scanned image of A4, 720dpi, 24bit fullcolor, even if you have up to 128Mb of memory!) To work with such huge images, CamlImages provides image swaps, which can escape part of the images into files stored on the hard disk. A huge image is thus partitioned into several blocks and if there is not enough free memory, the blocks which have not been accessed recently are swapped to temporary files. If a program requests to access to such a swapped block, the library silently loads it back into memory.
By default, image swapping is disabled, because it slows down the programs. To activate this function, you have to modify Bitmap.maximum_live and Bitmap.maximum_block_size:

Bitmap.maximum_live is the maximum heap live data size of the program (in words)
Bitmap.maximum_block_size is the maximum size of swap blocks (in words).

For example, if you do not want to use more than 10M words (that is 40Mb for a 32bit architecture or 80Mb for a 64bit architecture), set Bitmap.maximum_live to 10000000. You may (and you should) enable heap compaction, look at the GC interface file, gc.mli, in the standard library for more details (you should change the compaction configuration).
Bitmap.maximum_block_size affects the speed and frequency of image block swapping. If it is larger, each swapping becomes slower. If it is smaller, more swappings will occur. Too large and too small maximum_block_size, both may make the program slower. I suggest to have maximum_block_size set to !Bitmap.maximum_live / 10.
If you activated image swapping, cache files for unused swapped blocks will be removed automatically by Caml GC finalization, but you may free them explicitly by hand also. The functions and methods named "destroy" will free those blocks.
The swap files are usually created in the /tmp directory. If you set the environment variable "CAMLIMAGESTMPDIR", then its value replaces the default "/tmp" directory. The temporary files are erased when the program exits successfully. In other situations, for instance in case of spurious exception, you may need to erase temporary files manually.

3. Miscellaneous

3.1 Examples of use of the library ?

You can find some examples in the examples directory including image auto-cropping, resizing and an image viewer with the lablgtk library.

3.2 How do I organize my Makefile to use the library ?

Put the following line at the top of your Makefile:

	include /usr/local/lib/ocaml/camlimages/Makefile.config

The library directory can be different, if the library is installed somewhere else. The variables COMPFLAGS_CAMLIMAGES and LINKFLAGS_CAMLIMAGES are defined in Makefile.config; you should add them to the compiler and linker options. A sample Makefile is available as sample/Makefile.sample.