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This program is part of Netpbm.
pamcat reads one or more Netpbm images as input, concatenates them either left to right or top to bottom, and produces a single Netpbm image as output.
Options -leftright and -topbottom determine the direction of the concatenation.
The images do not have to be the same shape: You can concatenate images of different widths top to bottom and of different heights left to right. You can concatenate images of different depths (numbers of planes). You can concatenate a PBM image with a PPM image. Et cetera.
The format of the output image is the highest of the formats of the input images, in the order PBM, PGM, PPM, PAM.
For PAM output, if all of the input images have the same tuple type (including implied tuple types of PNM images), that is the tuple type of the output. If the inputs differ, but are all visual tuple types, the output's tuple type is the most primitive that can represent all the input. E.g. if inputs are GRAYSCALE and RGB, the output is RGB, and if the inputs are GRAYSCALE_ALPHA and RGB, the output is RGB_ALPHA. If the inputs differ and are not all visual, the output tuple type is a null string.
When the output is PAM, its depth is the maximum of the depths of the inputs (including implied depths of PNM images), but at least enough to represent the tuple type specified above. In the case of nonvisual PAM output, input images are padded to this output depth with higher numbered planes of all zeroes.
Where the input images are of different widths and you concatenate top to bottom, pamcat generates output as wide as the widest of the inputs and pads the narrower ones. The images can be justified either left, right, or center within this padded field. Use options -jleft, -jright, and -jcenter to control this.
Similarly, where the input images are of different heights and you concatenate left to right, pamcat generates output as tall as the tallest of the inputs and pads the shorter ones. The images can be justified either top, bottom, or center within this padded field. Use options -jtop, -jbottom, and -jcenter to control this.
You can make the padding black or white or let pamcat determine a likely background color, with possibly different colored padding for each input image. Control this with the -black and -white options.
Where the output image contains transparency information (because at least one of the input images does), the padding is opaque. (That is consistent with the result for an output image without transparency information, because such an image is defined to be opaque).
The arguments are names of input files. Any one of these, but not more than one, may be "-" to indicate Standard Input. If you have no arguments (and do not specify -listfile), that means a single input image from Standard Input (and that is pointless - the output is the same as the input). You can supply the file names in a file instead of as arguments with a -listfile option.
Regardless of how you specify the input files, you may not concatenate more files than your system's limit on the number of concurrently open files by one process. 16 is a typical number for that.
To assemble a regular grid of images, you can use pamundice.
To do the reverse, you might use pamdice to split an image up into smaller ones of equal size or pamcut to chop off part of an image or extract part of an image.
pnmtile concatenates a single input image to itself repeatedly.
In addition to the options common to all programs based on libnetpbm (most notably -quiet, see Common Options), pamcat recognizes the following command line options:
You must specify the direction by specifying one of the above. You cannot specify both.
You cannot specify this with -jright
This option is invalid in a left-right concatenation.
You cannot specify this with -jleft
This option is invalid in a left-right concatenation.
You cannot specify this with -jbottom
This option is invalid in a top-bottom concatenation.
You cannot specify this with -jtop
This option is invalid in a top-bottom concatenation.
By default, pamcat centers the smaller images. -topbottom -jleft would stack the images on top of each other, flush with the left edge. -leftright -jbottom would line up the images left to right with their bottom edges aligned as if sitting on a table.
You may not specify this with -black
You may not specify this with -white
The file contains one file name per newline-delimited line in whatever code the system fopen service expects. You may omit the newline on the last line. Empty lines are ignored. There is no mechanism for including comments in the list (so if you want to have a commented list, preprocess it to remove comments before supplying it to pamcat).
You may not specify file names as command line arguments together with -listfile
You may not list more files than than your system's limit on the number of concurrently open files by one process. 16 is a typical number for that.
This option was new in Netpbm 11.01 (December 2022).
pamcat was new in Netpbm 11.00 (September 2022); in earlier versions, pnmcat does most of the same thing.
Primordial Netpbm/Pbmplus contained concatenation tools, but there were two of them: pbmcatlr for left-right concatenation of PBM images and pbmcattb for top-bottom concatenation. When the PGM and PPM formats were added, these programs were combined and extended to handle all three formats, as pnmcat. All of this work was done by Pbmplus author Jef Poskanzer.
In Netpbm 10.44 (September 2008), Akira F Urushibata added special fast processing for raw PBM images, exploiting bitstring processing CPU facilities.
pnmcat was one of the most essential programs in Netpbm, but one thing it could not concatenate was PAM images with transparency. So in Netpbm 11.00 (September 2022), Bryan Henderson wrote pamcat to replace it. It reused the raw PBM fast path code from pnmcat almost verbatim.