Read me – Image Processing


– JPEG

is the standard method for lossy compression of grayscale and color images. It is supported natively in all browsers, and uses a good open source compression library. Decompression is supported by the rasterizers in PS and PDF, for level 2 and above. It has a progressive
mode that compresses about 10% better than standard, but is considerably slower to decompress. See jpegio.c.

– PNG

is the standard method for lossless compressio of binary, grayscale and color images. It is supported natively in all browsers, and uses a good open source compression library (zlib). It is superior in almost every respect to GIF (which, until recently, contained proprietary LZW compression). See pngio.c.

– TIFF

is a common interchange format, which supports different depths, colormaps, etc., and also has a relatively good and widely used binary compression format (CCITT Group 4). Decompression of G4 is supported by rasterizers in PS and PDF,level 2 and above. G4 compresses better than PNG for most text and line art images, but it does quite poorly for halftones. It has good and stable support by Leffler’s open source library, which is clean and small. Tiff also supports multipageimages through a directory structure. See tiffio.c

– BMP

has (until recently) had no compression. It is a simple format with colormaps that requires no external libraries.It is commonly used because it is a Microsoft standard, but has little besides simplicity to recommend it. See bmpio.c.

– PNM

is a very simple, old format that still has surprisingly wide use in the image processing community. It does not support compression or colormaps, but it does support binary, grayscale and rgb images. Like BMP, the implementation is simple and requires no external libraries. See pnmio.c.

– GIF

is still widely used in the world. With the expiration of the LZW patent, it is practical to add support for GIF files.The open source gif library is relatively incomplete and unsupported (because of the Sperry-Rand-Burroughs-Univac patent history). See gifio.c.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s