1. CS430 © 2006 Ray S. Babcock Lossy Compression Examples JPEG MPEG JPEG MPEG

2. CS430 © 2006 Ray S. Babcock JPEG  Joint Photographic Experts Group  Defines three different coding systems  Lossy baseline coding system  Extended coding system for greater compression  Lossless independent coding system for reversible applications  Baseline performed in three sequential steps  DCT (Discrete Cosine Transform) computation  Quantization  Variable-length code assignment  To start, the image is divided into pixel blocks of size 8x8 (left to right, top to bottom)  Joint Photographic Experts Group  Defines three different coding systems  Lossy baseline coding system  Extended coding system for greater compression  Lossless independent coding system for reversible applications  Baseline performed in three sequential steps  DCT (Discrete Cosine Transform) computation  Quantization  Variable-length code assignment  To start, the image is divided into pixel blocks of size 8x8 (left to right, top to bottom)

3. CS430 © 2006 Ray S. Babcock JPEG (cont.)  Gray levels are shifted to center: –L/2 <= gl <= L/2  DCT is run on the block producing frequency components centered on upper left corner.  The DCT 2D block is converted into a 1D string by using a zig-zag pattern.  The array is quantized.  A selected number of coordinates is selected depending on the “quality” desired.  These values are then encoded using a variable length coding system.  The binary codes are transmitted.  Gray levels are shifted to center: –L/2 <= gl <= L/2  DCT is run on the block producing frequency components centered on upper left corner.  The DCT 2D block is converted into a 1D string by using a zig-zag pattern.  The array is quantized.  A selected number of coordinates is selected depending on the “quality” desired.  These values are then encoded using a variable length coding system.  The binary codes are transmitted.

4. CS430 © 2006 Ray S. Babcock JPEG Coding Example 52 55 61 66 70 61 64 73 63 59 66 90 109 85 69 72 62 59 68 113 144 104 66 73 63 58 71 122 154 106 70 69 67 61 68 104 126 88 68 70 79 65 60 70 77 68 58 75 85 71 64 59 55 61 65 83 87 79 69 68 65 76 78 94 8x8 block of original image

5. CS430 © 2006 Ray S. Babcock JPEG Coding Example -76 -73 -67 -62 -58 -67 -64 -55 -65 -69 -62 -38 -19 -43 -59 -56 -66 -69 -60 -15 16 -24 -62 -55 -65 -70 -57 -6 26 -22 -58 -59 -61 -67 -60 -24 -2 -40 -60 -58 -49 -63 -68 -58 -51 -65 -70 -53 -43 -57 -64 -69 -73 -67 -63 -45 -41 -49 -59 -60 -63 -52 -50 -34 Level Shifted

6. CS430 © 2006 Ray S. Babcock JPEG Coding Example -415 -29 -62 25 55 -20 -1 3 7 -21 -62 9 11 -7 -6 6 -46 8 77 -25 -30 10 7 -5 -50 13 35 -15 -9 6 0 3 11 -8 -13 -2 -1 1 -4 1 -10 1 3 -3 -1 0 2 -1 -4 -1 2 -1 2 -3 1 -2 -1 -1 -1 -2 -1 -1 0 -1 DCT

7. CS430 © 2006 Ray S. Babcock JPEG Coding Example -26 -3 -6 2 2 0 0 0 1 -2 -4 0 0 0 0 0 -3 1 5 -1 -1 0 0 0 -4 1 2 -1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 DCT Normalized

8. CS430 © 2006 Ray S. Babcock JPEG Coding Example -26 -3 -6 2 2 0 0 0 1 -2 -4 0 0 0 0 0 -3 1 5 -1 -1 0 0 0 -4 1 2 -1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 DCT Normalized -26 -3 1 -3 -2 -6 2 -4 1 -4 1 1 5 0 2 0 0 -1 2 0 0 0 0 0 -1 -1 EOB EOB indicates remainder are zeros.

9. CS430 © 2006 Ray S. Babcock JPEG Coding Example  Now using a version of Huffman coding categories and DC differences, you have the sequence  1010110 0100 001 0100 0101 100001 0110 100011 001 100011 001 001 100101 11100110 110110 0110 11110100 000 1010  Total number of bits in completely coded reordered array (and thus the number of bits necessary to represent the entire 8x8, 8-bit example sub image) is 92.  The resulting compression ration is 512/92 or about 5.6 : 1  Now using a version of Huffman coding categories and DC differences, you have the sequence  1010110 0100 001 0100 0101 100001 0110 100011 001 100011 001 001 100101 11100110 110110 0110 11110100 000 1010  Total number of bits in completely coded reordered array (and thus the number of bits necessary to represent the entire 8x8, 8-bit example sub image) is 92.  The resulting compression ration is 512/92 or about 5.6 : 1

10. CS430 © 2006 Ray S. Babcock JPEG Dcompression  Recreate the normalized transform coefficients using a lookup table.  Denormalize that array.  Reverse Discrete Cosine Transform.  Level shift back to normal 0-255 range.  If you do that, you have something like the original image, but not exact!  Recreate the normalized transform coefficients using a lookup table.  Denormalize that array.  Reverse Discrete Cosine Transform.  Level shift back to normal 0-255 range.  If you do that, you have something like the original image, but not exact!

11. CS430 © 2006 Ray S. Babcock JPEG 2000  Extends the initial JPEG standard to provide increased flexibility in both the compression of continuous tone still images and access to the compressed data.  E.g. portions of a JPEG 2000 compressed image can be extracted for retransmission, storage, display, and/or editing.  The standard is based on the wavelet coding techniques.  Extends the initial JPEG standard to provide increased flexibility in both the compression of continuous tone still images and access to the compressed data.  E.g. portions of a JPEG 2000 compressed image can be extracted for retransmission, storage, display, and/or editing.  The standard is based on the wavelet coding techniques.