Understanding various Image Codecs

July 1, 2008

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

  1. Good photo quality.
  2. 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.
  3. Bitmap codecs may translate well to dot-format output devices such as CRTs and printers.

Cons

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


GIF

Pros

  1. This codecs allows you to create transparent, interlaced, and animated graphics for the Web
  2. 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.
  3. 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:

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


JPEG

Pros

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

Cons

  1. Single Resolution & Single Quality
  2. No target bit rate
  3. Blocking artifacts at low bit rate
  4. No lossless capability
  5. Poor error resilience
  6. No tiling & No regions of interest


JPEG 2000

Pros:

  1. Improved coding efficiency
  2. Full quality scalability
  3. From lossless to lossy at different bit rate
  4. Spatial scalability
  5. Improved error resilience compared to jpeg
  6. Tiling & Region of interests

Cons:

  1. Requires more in memory compared to JPEG.
  2. Requires more computation time


MJPEG

Pros

  1. 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.
  2. At WWW data rates (5-20K), JPEG may produce better results than Cinepak.

Cons

  1. 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.
  2. Large image and/or high frame rate movies usually don’t play smoothly.


TIFF

Pros:

  1. 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.
  2. 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:

  1. Codecs produce large file size


PNG

Pros:

  1. 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.
  2. It is a best one for creating complex live transparency, high-color graphics, and better compressed low-color graphics.
  3. Designed to be network-friendly, so it is recognized and supported on all platforms.

Cons:

  1. It doesn’t support animation
  2. It does not use predictive frames
  3. 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.