Metapixel 1.0.2 =============== Metapixel is a program for generating photomosaics. It can generate classical photomosaics, in which the source image is viewed as a matrix of equally sized rectangles for each of which a matching image is substitued, as well as collage-style photomosaics, in which rectangular parts of the source image at arbitrary positions (i.e. not aligned to a matrix) are substituted by matching images. Installation ------------ To compile Metapixel, you need, in addition to a C compiler, libpng, libjpeg, and giflib. To run the script for preparing constituent images, you will additionally need Perl. Most Linux distributions contain these software packages. On MacOS X, you can get them with Fink (http://fink.sourceforge.net/). Edit the first line of Makefile if you want to install Metapixel somewhere else than /usr/local. Then, type make If everything compiled fine, become root and type make install Configuring Metapixel --------------------- You can optionally create a file ".metapixelrc" in your home directory to store some settings which makes it easier to use Metapixel, since you won't have to use that many switches on the command line. A sample configuration file is included in the Metapixel distribution under the name "metapixelrc". See the section "The Configuration File" below for details. It is advisable to at least set the options "prepare-directory" and "library-directory". Preparing images ---------------- Before (non-anti-mosaic) mosaics can be created, the constituent images need to be preprocessed. Preparing an image does two things. Firstly, it computes various coefficients by which the image can be matched against a part of a source image. Secondly, the image is scaled to a smaller size. Usually this will be the size you intend to use for it in the target image, but it can be any arbitrary size. It makes sense to scale your images to the maximum size that you will use for constituent images. That way, no information gets lost. The default size is 128x128 pixels. The matching data and the scaled images are stored in a directory which is then called a "library". You can use more than one library in the creation of a mosaic. To simplify the task of creating a library, the Perl script 'metapixel-prepare' is included in the distribution. It must be called with the name of the directory where your original images are stored in. As a second argument you must give the directory of the library to which the images are to be added. If you have set a default directory for preparing images in your configuration file, the second argument is optional. If the script is called with the option "--recurse", it searches the directory with the original images recursively, i.e., it searches all its direct and indirect subdirectories as well. It also accepts parameters specifying the size of the scaled down images. Just call it - it prints out usage information. If the script constantly complains that an error occurred when running 'metapixel', that probably means that metapixel is not in your path. The other possibility is that all your images are in a format that Metapixel doesn't like (it only supports JPEG, PNG, and GIF). Creating photomosaics --------------------- Input images for mosaics can have arbitrary sizes. Should you want the created mosaic to be of a different size than the input image, use the --scale option. It scales the input image uniformly in both directions (i.e. obeying the aspect ratio). If the width or height of the input image after scaling are not multiples of the width and height of the constituent images, the input image is further scaled up to the smallest size (larger than the input image) that obeys this constraint, possibly changing the aspect ratio a bit. This does not apply to collages, however. The sizes of their source images after scaling are always left untouched. Metapixel produces output images in the PNG or JPEG formats, depending on the extension of the output file name. In order to create a classic photomosaic for the image input.jpg and write the output to output.png with constituent images stored in the directory "images", use the following command line: metapixel --library images --metapixel input.jpg output.png To create a collage use metapixel --library images --collage --metapixel input.jpg output.png Using the -y, -i and -q options you can change the weights for each of the color channels. For example, to match only luminance, completely disregarding chrominance, use metapixel --library images -i0 -q0 --metapixel input.jpg output.png The default weight for each of the channels is 1. Using the --cheat option you can specify the percentage by which the resulting photomosaic should be overlayed by the original image. The default is 0, i.e., the photomosaic is not overlayed at all. A percentage of 100 yields, not surprisingly, the original image. A percentage of 30 makes the photomosaic appear noticably better but is yet small enough to go unnoticed without close inspection in most circumstances. As of version 0.6, Metapixel implements two different matching algorithms. The new metric, which is a trivial distance function, seems to give better results while not being slower than the old wavelet metric. The metric can be chosen using the --metric option. The default is the new subpixel metric. You can use the --library option more than once to let Metapixel use more than one library for a mosaic. Classic Mosaics --------------- Metapixel allows you to choose between two algorithms for finding matching images, via the --search option. The old algorithm called "local" simply selects the best matching image for each location, possibly disregarding images selected in locations nearby (see below). The new algorithm called "global" repeats the following step until all locations have been assigned to: Find the best match for any location among all small images that have not already been used. This guarantees that no small image is used twice. Obviously, it also means that you must have at least as many small images as there are locations in the image. Note that "global" is much slower and uses more memory than "local". The "--distance" option lets you specify the minimal distance between two occurences of the same constituent image in the target image for the "local" algorithm. Distance 0 means that it is allowed for the same image to occur in adjacent positions in the matrix. The default distance is 5, which means that there must be at least 5 images "between" two occurences of the same image in the matrix. Note that Metapixel is forced to select non-optimal matches for distances greater 0. Antimosaics ----------- Antimosaics are classic mosaics for which the small images are the parts of a single image, possibly the input image itself, and can be created using the --antimosaic option. Metapixel subdivides the antimosaic file as if it were doing a mosaic of that file, but then uses the resulting subimages as the small images for a classic mosaic. In case the antimosaic image and the input image are the same, Metapixel will simply reconstruct the input image from the subimages, because they will always match best in their original locations. To tell Metapixel to do otherwise, you can use the --forbid-reconstruction option, which allows you to specify a minimum distance between the original location of a subimage and the location it has in the resulting mosaic. Here's how you create an antimosaic with a minimum reconstruction distance of 2: metapixel --library images -x input.jpg -f 2 --metapixel input.jpg output.png The Configuration File ---------------------- The first thing Metapixel does is try to read the file ".metapixelrc" in your home directory. From this file, it reads default values for its settings, so that you don't have to give them on the command line each time you use Metapixel. In this configuration file, you can use the following directives: (prepare-directory ) The library directory which metapixel-prepare should use by default. metapixel-prepare does not automatically create the directory if it doesn't exist, so make sure it does. (prepare-dimensions ) The size metapixel-prepare should use for the small images. (library-directory ) A library directory which Metapixel should use when creating mosaics. You can use this directive more than once. (small-image-dimensions ) The dimensions of the small images Metapixel should use in mosaics. (yiq-weights ) The weights for the channels to be used in matching images. (metric ) The metric Metapixel should use for matching images. This can either be "subpixel" or "wavelet". (search-method ) The search method for creating classic mosaics. This can either be "local" or "global". (minimum-classic-distance ) The minimum distance between two occurences of the same image in classic mosaics with the local search method. (minimum-collage-distance ) The minimum distance (in pixels) between two occurences of the same image in collage mosaics. (cheat-amount ) The cheat amount in percent. (forbid-reconstruction-distance ) The minimum distance between the position of subimage in the original image and its position in the output image in an antimosaic. Take a look at the file "metapixelrc" in the distribution. It gives examples for each of the directives discussed here. Collages -------- To create a collage, you have to use the "--collage" option in addition to "--metapixel". You can also specify a minimum distance between two occurences of the same image, which is measured in pixels. The default value is 256. Use the "--distance" option to change it. Note that the distance is measured between the centers of the images, not their edges, i.e., a minimum distance of 10 means that the centers of two occurences of the same image must be at least 10 pixels apart. This will usually mean that they are allowed to overlap, unless you use very tiny small images. Note that Metapixel uses ridiculous amounts of memory for collage mosaics. To create a collage photomosaics of size 2048x2048 your machine should at least have 64MBytes RAM. Protocols --------- Metapixel can, in addition to producing a classical mosaic, write a file specifying which small images it put in each of the locations. This protocol file can then be used to reproduce the mosaic without doing the matching again, for example to experiment with different cheat amounts. The protocol also contains information on how good each small image matches the original location, so you can find out where the matches are good and where they aren't. You can also modify the protocol and let metapixel generate a mosaic which it wouldn't have matched itself, for whatever reason you might want to do this. Use the --out option to create a protocol and the --in option to reproduce a mosaic from a protocol. The protocol file is a LISP list with the following syntax: (mosaic (size ) (metapixels . )) and are the number of small images in the mosaic across the width and height of the mosaic, respectively. is a list containing lists with the following syntax: ( ) and are the position of the small image. The upper left small image has coordinates (0,0), the lower right (-1,-1). and must both be 1 in this version of Metapixel. is the name of the small image file. A typical line in the protocol file looks like this: (30 23 1 1 "semiharmless.new/wallpaper07.jpg.png") ; 4792.000000 The number at the end of the line is the matching score. The lower the score, the better the match. Note that the semicolon ';' introduces a comment which lasts ends with the end of the line, so the matching score is not part of the protocol syntax. The matching algorithms ----------------------- The algorithm that does the image matching via wavelets is described in the paper 'Fast Multiresolution Image Querying' by Charles E. Jacobs, Adam Finkelstein and David H. Salesin. The new subpixel metric is very trivial. I suggest you consult the source if you are interested in it. The matching function is subpixel_compare(). Sorting Images by Size or Aspect Ratio -------------------------------------- Metapixel comes with a tool called `metapixel-sizesort' which sorts images by size or aspect ratio by moving them to directories containing only files with similar size or aspect ratio. An example: Let's say you have thousands of images in /my/images, and you want them sorted by aspect ratio and placed in /my/sorted/images. You can do this with this command: metapixel-sizesort --ratio=2 /my/images /my/sorted/images The option `2' to ratio tells metapixel-sizesort to put all those images together whose aspect ratios are the same with an accuracy of two places behind the comma. You might now have (among others) a directory called /my/sorted/images/ratio_0.79 which contains all images whose ratio between width and height is about 0.79. Upgrading from versions 0.8/0.9/0.10 ------------------------------------ Starting from release 0.11, Metapixel requires that the tables file is in the same directory as the small images described in that file. If your configuration is different, all you need to do is to make sure that all these files are in the same directory. You don't need to remove the paths in the tables file, as Metapixel does that automatically. Upgrading from versions 0.6/0.7 ------------------------------- The tables file format has changed in Metapixel 0.8, but you don't need to run 'metapixel-prepare' again. There's a program called 'convert' included in the distribution that does the job. Just tell it which size your small images are, give it the old tables file on stdin and it writes the new one on stdout. For example, if your small images are 128 pixels wide and 96 pixels high, go to the directory with the tables file (usually the directory where the small images are) and do convert --width=128 --height=96 tables.mxt Licence and Availability ------------------------ Metapixel is free software distributed under the terms of the GPL. The file `COPYING' contains the text of the license. The source of Metapixel is available at the Metapixel homepage at http://www.complang.tuwien.ac.at/schani/metapixel/ --- Mark Probst schani@complang.tuwien.ac.at