JPEG VS JPEG 2000??

We all know about  JPEG as we use it in our daily live. When we say JPEG, automatically we will think about images and pictures. However, what about JPEG2000? Have what do you understand about that?


Well, JPEG 2000 is basically a new standard or update for the well-known JPEG (Joint Photographic Expert Group) image standard. The name might be almost the same but truth be told, there are many differences between them. 

What you should know about JPEG2000? Well here’s some of its features:

• Better efficiency in compression (incl. 48 bit color depth support)
• Possibility of lossless compression
• Decoding with different output resolutions
• A process to calculate the integrated bit rate (possibility of reaching an aimed bit rate)
• Dividing the image into smaller parts to be coded independently from the others
• Improvement in noise resilience
• Access to the compressed bit rate at any point in order to access the image directly
• Better performances in coding/decoding through many different cycles
• More flexible file format

The basic that we should know but don’t really care is the fact that in the lossy image compression mode, JPEG2000 is based on discrete wavelet transformation which is supposed to be more efficient compared to the JPEG algorithm cosine transformation. What does this mean? It means you can view it with different resolution and size based on the same image file! Why do you should know this? One application that this fact is useful is if you have a slow internet connection, you can view the image with a lower resolution as it saves time compared to higher resolution which takes long time to load. Bla bla bla.. OK! enough words! Lets look at the image below! =)

All the above images are viewing from a single JPEG2000 image with different size and resolution. We can see that the quality is good. We cant really do this with JPEG except if we edit the resolution or size in Photoshop. =p

From the picture above, we can see that the image after compression for JPEG2000 retain a much higher quality than JPEG.

 JPEG 2000 offers both lossy and lossless compression in the same file stream, while JPEG usually only utilizes lossy compression. JPEG does have a lossless compression engine, but it is separate from the lossy engine, and is not used very often. Thus, when high quality is a concern, JPEG 2000 proves to be a much better compression tool. Because of the way the compression engine works, JPEG 2000 promises a higher quality final image, even when using lossy compression. Since the JPEG 2000 format includes much richer content than existing JPEG files, the bottom line effect is the ability to deliver much smaller files that still contain the same level of detail as the larger original JPEG files. The JPEG 2000 files can also handle up to 256 channels of information as compared to the current JPEG standard, which, by reason of common implementation, is limited to only RGB (red, green, and blue) data.

 JPEG 2000 over JPEG is that JPEG 2000 is able to offer higher compression ratios for lossy compression.  For lossy compression, data has shown that JPEG 2000 can typically compress images from 20%-200% more than JPEG.  Compression efficiency for lossy compression is typically measured using the peak signal to noise ratio, or PSNR, and the root mean square error (RMSE).  This method seeks to take into account the visual quality retained by the compression method, as well as how much the image was compressed.  The formula for the PSNR compression efficiency, in dB, is shown below, where b is the bit depth of the original image.

Another advantage of JPEG 2000 is its ability to display images at different resolutions and sizes from the same image file as i said earlier.  With JPEG, an image file was only able to be displayed a single way, with a certain resolution.  Because JPEG 2000 is based on wavelets, the wavelet stream can be only partially decompressed if the user only wants a low-resolution image, while the full resolution image can be viewed if this is desired.  

 An example of some PSNR efficiencies for JPEG 2000 and JPEG is shown in Table 1.  Two different color images were compressed using several different bit rates (measured in bits per pixel, or bpp) using both JPEG 2000 and JPEG.  A higher bit rate will result in a higher quality picture.  The analysis was performed by Maryline Charrier, Diego Santa Cruz, and Mathias Larsson as part of an overview of JPEG 2000.  The results indicate that JPEG 2000 consistently offers a higher compression efficiency.  One should note that since the PSNR is measured on a log scale, the data in Table 1 indicates that in actuality the test showed that JPEG 2000 compresses almost twice more than JPEG. JPEG 2000 is also able to offer compression ratios of about 2.5:1 for lossless compression, whereas JPEG was not able to satisfactorily perform lossless compression at all.  Lossless compression ratios are simply measured by how much less memory the compressed image uses.

 Table 1  Comparison of PSNR compression efficiencies
(in dB) for two images at various bit rates

Another benefit of JPEG 2000 is its ROI capability, or Region of Interest.  The use of wavelets allows one to be able to select a certain area of an image to view at a high quality, while leaving the rest of the image at a lower quality.  This allows the user to only view a necessary portion of the image instead of the entire image.  This significantly reduces the amount of memory the image requires, and the amount of time required to access the image.

Finally, lets talk about ER. Im sorry, i did not mean EMERGENCY ROOM. ER that i am talking about is Error resilience, which measures the ability of a compression method to avoid letting errors introduced into the image file affect the quality of the image.  For example, when downloading an image from the Internet, background “noise” may be introduced into the image file, causing some small errors.  Conversion of the file for use in another application is another way in which small errors may be brought into the image file.  JPEG 2000 offers significantly higher error resilience than JPEG; therefore, there is less chance that the image will be somehow corrupted and its quality sacrificed in some way.

Thats all for this week. Take care!