Path: EDN Asia >> Design Centre >> IC/Board/Systems Design >> A primer on image compression
IC/Board/Systems Design Share print

A primer on image compression

20 Feb 2015  | Sunny Aggarwal, Gourav Modi

Share this page with your friends

DCT on 8x8 block
Steps to be performed:

 • Take a 8x8 matrix of an image and fetch its value from 0 to 256
 • Scale it down to -128 to 127 level
 • Ready to perform the DCT matrix ( D= TMT' )
 • Quantisation
An 8x8 block of DCT is compressed using quantisation. A remarkable feature of JPEG Process is : the varying levels of image compression and quality is obtainable by using different quantisation matrix.

Example of a Quantisation matrix:

After calculating the DCT equivalent of an image, the matrix is divided by the quantisation matrix to the nearest integer (lossy) and thereby making the higher frequency content to be nearly zero.

The matrix is ready for the final step of compression. Before storage, the coefficients are converted to a stream of binary data. After quantisation, the higher frequency components become zero, JPEG takes advantage of this by encoding quantised coefficients in the zigzag sequence

Figure 6: Zigzag sequence for coding.

RLE algorithm is applied to condense sequences of identical values. Finally, Huffman compression is done to the remaining sequence which encodes frequently used values using lesser bits than infrequently used values.

Figure 7: Encoding using RLE.

About the authors
Sunny Aggarwal and Gourav Modi contributed this article.

 First Page Previous Page 1 • 2 • 3 • 4

Want to more of this to be delivered to you for FREE?

Subscribe to EDN Asia alerts and receive the latest design ideas and product news in your inbox.

Got to make sure you're not a robot. Please enter the code displayed on the right.

Time to activate your subscription - it's easy!

We have sent an activate request to your registerd e-email. Simply click on the link to activate your subscription.

We're doing this to protect your privacy and ensure you successfully receive your e-mail alerts.

Add New Comment
Visitor (To avoid code verification, simply login or register with us. It is fast and free!)
*Verify code:
Tech Impact

Regional Roundup
Control this smart glass with the blink of an eye
K-Glass 2 detects users' eye movements to point the cursor to recognise computer icons or objects in the Internet, and uses winks for commands. The researchers call this interface the "i-Mouse."

GlobalFoundries extends grants to Singapore students
ARM, Tencent Games team up to improve mobile gaming

News | Products | Design Features | Regional Roundup | Tech Impact