JPEG - JPEG2000 Isabelle Marque JPEGJPEG2000

JPEG Joint Photographic Experts Group Committe created in 1986 by: International Organization for Standardization (ISO) and International Telecommunication Union (ITU) A working group which creates the standard for still image compression

JPEG - JPEG2000 Two different standards Major differences : JPEGJPEG2000 Created for natural imagery Discrete Cosine Transform algorithm Created for computer generated imagery Discrete Wavelet Transform algorithm

JPEG Architecture of standard Forward transform Quantization Entropy coding  DC coefficient  AC coefficients Entropy encoding Source image data Forward transform Quantization Compressed image data

JPEG Forward transform 1. Level shifted 2. Divided into blocks of 8*8 pixels 3. Forward DCT: Entropy encoding Source image data Forward transform Quantization Compressed image data

JPEG DCT basis functions

JPEG Original image

JPEG DCT coefficients

JPEG Quantization  Quantization table  Zigzag scan Entropy encoding Source image data Forward transform Quantization Compressed image data

JPEG Quantization table

JPEG Labels after quantization

JPEG Entropy encoding DC coefficient and AC coefficients are coded differently DC coefficient  Encode the difference  Huffman code unmanageable  First bits to define the category and other bits to define the element in the category CategoryPossible values Entropy encoding Source image data Forward transform Quantization Compressed image data

JPEG AC coefficients Defined by a certain number of terms:  Category C that a non zero label falls in  Z: number of zero since the last non zero label  Z/C points to a specific code  Follows by bits to define the element in the category  +1 code  EOB stands for End Of Block: A code after the last non zero value

JPEG Sample table for obtaining the huffman code Z/CCodewordZ/CCodeword 0/0 (EOB)1010 0/1001/ /2011/ /31001/ /410111/ / /

JPEG Reconstructed image

JPEG More accurate image  Increase the bit rate  Decrease quantization table elements Less accurate image  Decrease the bit rate  Increase quantization table elements Problem: Low rate image: « blockiness »

JPEG2000 Can be both lossless and lossy Improves image quality Uses a layered file structure :  Progressive transmission  Progressive rendering File structure flexibility:  Could use for a variety of applications Many functionalities

JPEG2000 Architecture of standard Forward transform Quantization Entropy coding Entropy encoding Source image data Forward transform Quantization Compressed image data

JPEG2000 Forward transform 1. Level shifted 2. Divided into blocks 3. Forward Discrete Wavelet Transform Entropy encoding Source image data Forward transform Quantization Compressed image data

JPEG2000 Details

JPEG2000

Discrete Wavelet Transform can be :  Irreversible: Daubechies 9-tap/7-tap filter  Reversible: 5-tap/3-tap filter  Any user could supply wavelet filter banks

JPEG2000 Quantization Dynamic range: depends on the number of bits and the choice of the wavelet Exponent Mantissa Entropy encoding Source image data Forward transform Quantization Compressed image data

JPEG2000 Entropy encoding Embedded Block Coding with Optimization Truncation of the embedded bit stream (EBCOT)  Each subband is divided into rectangular blocks which are coded independently called code blocks  Bitstream is organized in a succession of layers  Each layer corresponds to a certain distortion level  The quality of the reproduction is proportional to the numbers layers received Entropy encoding Source image data Forward transform Quantization Compressed image data

JPEG2000 Layered structure

JPEG - JPEG Quality At compression ratio: 43:1 JPEGJPEG2000

JPEG - JPEG Quality Method of picture quality measurement:PSNR Peak Signal To Noise Ratio in dB: Pixel of the image Pixel of the reconstructed image Size of the image Root Mean Squared Error

JPEG - JPEG Quality Comparison of PSNR values (dB) compressed colour images Bits per pixel Lena JPEG Lena JPEG

CONCLUSION – Key points JPEG: DCT algorithm JPEG2000: DWT algorithm  Layered structure  Many functionalities For a similar quality of PSNR, JPEG2000 compresses almost twice more than JPEG

REFERENCES Introduction to Data Compression, K. Sayood, Morgan Kauffman, Second Edition, (Primary) A.N. Skodra, C.A. Christopoulos, T. Ebrahimi, « JPEG2000, the upcoming still image compression standard », Proceeding of the 11th Portuguese Conference on Pattern recognition, Porto, Portugal, May 11th-12th, pp , 2000 JPEG, Official site: Home page of a member: PSNR: g2.pdfhttp:// g2.pdf Quality: