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Friday, June 27, 2008

Understanding Various Image Codecs

The Image codecs is a method of compression/decompression of image files or image data. The codecs stands for Coders / Decoders.

There are various kinds of image codecs available. Since these codecs have been implemented by different algorithms by number of companies; they have different specification and application in various fields.

The various software image codecs are:

  • Bmp
  • Gif
  • JPEG
  • JPEG 2000
  • MJPEG
  • TIFF
  • PNG
  • WBMP
These various Image codecs are technically differentiated from each other based on various factors which includes compression technology / algorithm, platform supported, sampling, OS supported etc One can easily find in-depth details on Wikipedia for each of image codecs. Here is a illustration of image codecs with their pros & cons?


BMP

Pros

  • Good photo quality.
  • Bitmap files (bmp) may be easily created from existing pixel data stored in an array in memory. Pixel values may be modified individually or as large groups by altering a palette if present.
  • Bitmap codecs may translate well to dot-format output devices such as CRTs and printers.

Cons

  • Bmp codecs are Limited to RGB-images.
  • These codecs generally does not support effective image compression. They can be very large, particularly if the image contains a large number of colors.
  • It’s also not supported well across multiple platforms.
  • Shrinking this image codecs by decimation (throwing away pixels) can change the image in an unacceptable manner.

GIF

Pros

  • This codecs allows you to create transparent, interlaced, and animated graphics for the Web
  • Compresses by scanning horizontally across a row of pixels and finding solid areas of color. Indexes the pixels based on the 256 color palette in the file. No image information is lost.
  • The only graphic file format (codec) that is universally supported by all graphical browsers, regardless of version. Most popular and versatile format for distributing color image on the Web.

Cons:

  • This codec is not good for photographic images due to its limited number of colors generally 256 colors.

JPEG

Pros

  • JPEG codec has low complexity. Picture quality is generally good enough.
  • This is also memory efficient. i.e. good compression allows to reduce the file size.
  • It works very well for “slide-show” movies that have a very low frame rate.
  • Also it has reasonable coding efficiency

Cons

  • Single Resolution & Single Quality
  • No target bit rate
  • Blocking artifacts at low bit rate
  • No lossless capability
  • Poor error resilience
  • No tiling & No regions of interest

JPEG 2000

Pros:

  • Improved coding efficiency
  • Full quality scalability
  • From lossless to lossy at different bit rate
  • Spatial scalability
  • Improved error resilience compared to jpeg
  • Tiling & Region of interests

Cons:

  • Requires more in memory compared to JPEG.
  • Requires more computation time

MJPEG

Pros

  • MJPEG codecs are often used as storage formats for large files that need to be archived with good quality. It is a lossy codec, but at 100% quality, the image degradation is minimal.
  • At WWW data rates (5-20K), JPEG may produce better results than Cinepak.

Cons

  • All the JPEG codecs require significant amounts of CPU power and are not well suited to video playback at CD-ROM or higher data rates, except when assisted by a hardware capture card.
  • Large image and/or high frame rate movies usually don’t play smoothly.

TIFF

Pros:

  • Compared to a JPEG, an uncompressed TIFF codec retains the best quality of a photographic image, making it ideal for digital masters (preservation) and print documents.
  • Low or high-resolution images codec of photographic quality (images containing many colors that blend and fade). Encoding scheme is Lossless; files can be compressed or uncompressed.

Cons:

  • Codecs produce large file size

PNG

Pros:

  • A better compression than GIF codec, which only scans rows. The compression is ‘lossless’, you do not lose color information as you compress the file smaller. Typically compresses images 5-25% better than GIF.
  • It is a best one for creating complex live transparency, high-color graphics, and better compressed low-color graphics.
  • Designed to be network-friendly, so it is recognized and supported on all platforms.

Cons:

  • It doesn’t support animation
  • It does not use predictive frames
  • It has lower quality than PICT or TIFF


To commercialize these image codecs couples of portals are available where you can compare and procure them. Such portals are design-reuse, chipestimates, IPsupermarket.com which allows you to buy/sell or license these image codecs.

1 comment:

Anonymous said...

Its really appreicable! good info