Pambackground User Manual
Pambackground User Manual
NAMESYNOPSIS
DESCRIPTION
OPTIONS
SEE ALSO
HISTORY
NAME
pambackground - create a mask of the background area of an image
SYNOPSIS
pambackground
[netpbmfile]
[-verbose=]
Minimum unique abbreviations of options are acceptable. You may use double hyphens instead of single hyphen to denote options. You may use white space in place of the equals sign to separate an option name from its value.
DESCRIPTION
This program is part of Netpbm(1)
pambackground reads a PNM or PAM image as input. It generates as output a PAM image that identifies the background area of the image (a mask).
To identify the background, pambackground assumes the image is a foreground image, smaller than the total image size, placed over a single-color background. It assumes that foreground image is solid -- it does not have holes through which the background can be seen. So in specific, pambackground first identifies the background color, then finds all contiguous pixels of that color in regions touching any edge of the image. Think of it as starting at each of the four edges and moving inward as far as possible until it hits pixels of another color (the foreground image).
pambackground identifies the background color as follows: If any 3 corners of the image are the same color, that’s the background color. If not, but 2 corners are the same color, the background color is the color of a pair of identically colored corners in this priority order: top, right, left, bottom. If no two corners have the same color, the background color is the color of the upper left corner.
In a typical photograph, the area that you would consider the background is many shades of a color, so to pambackground it is multiple colors and pambackground will not meaningfully identify the background of your image. To use pambackground in this case, you might use ppmchange to change all similar colors to a single one first. For example, if the photograph is a building against a blue sky, where nothing remotely sky-blue appears in the building, you could use ppmchange to change all pixels within 20% of ’SkyBlue’ to SkyBlue, then run pambackground on it.
In Release 10.37, pambackground does not really do what is promised above. It can’t see places where the background appears in the middle of a row (think of the sky between two buildings). From Release 10.38 forward, it snakes through whatever passages it has to to find all the background.
The PAM that pambackground creates has a single plane, with a maxval of 1. The sample value 1 means background; 0 means foreground. There is no tuple type. Some older programs (but none that are part of Netpbm) don’t know what a PAM is and expect a mask to be in the form of a PGM or PBM image. To convert pambackground’s output to PBM, use pamtopnm -assume. To convert to PGM, use pgmtopgm.
netpbmfile is the file specification of the input file, or - to indicate Standard Input. The default is Standard Input.
A common use for a background mask is with pamcomp. You could replace the entire background (or foreground) of your image with something else.
Another common use is to make an image with the background transparent (in some image format that has a concept of transparency; not Netpbm formats) so that image can be overlaid onto another image later. Netpbm’s converters to image formats that have transparency (e.g. PNG) let you use the mask that pambackground generates to identify the transparent areas for the output.
To simply make a mask of all the areas of a specified color, use ppmcolormask. If you have a unique background color (one that doesn’t occur in the foreground) and know what it is, this can create a background mask in cases that pambackground cannot: where there are see-through holes in the foreground image.
OPTIONS
-verbose
Tell interesting facts about the process.
SEE ALSO
ppmcolormask(1) , pamcomp(1) , pamtopnm(1) , pgmtopgm(1) , pnm(5) , pam(5) ,
HISTORY
pambackground was new in Netpbm 10.37 (December 2006).
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
