CODECs for images

• The Image codecs is a method of compression/decompression of image files or image data. The codecs stands for Encoders / Decoders.
• The various software image codecs are JPEG (JPG), GIF, PNG, BMP.The below figure shows the Encoding/Decoding concept.
• 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. Codecs divided into two types Lossy and Lossless.

Lossy codecs

• Lossy image codecs are JPEG and GIF when you performing on encoding and decoding on images we lose some quality of images.

1. JPEG (JPG)

Encoding/Compressing

Decoding/Decompressing

Advanatges

• 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.

Disadvanatges

• 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.

2. GIF

Encoding/Compressing

Decoding/Decompressing

Advanatges

• 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.

Disadvanatges

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

Codecs for Lossless

• Lossless codecs are PNG, BMP these are does not lose the data and quality when you are compressed.

1. PNG

Encoding/Compressing

Decoding/Decompressing

Advanatges

• 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.

Disadvanatges

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

2. BMP

Encoding/Compressing

Decoding/Decompressing

Advanatges

• 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.

Disadvanatges

• 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.