JPEG2005fall

1 JPEG(Joint Photographic Experts Group) ISOIEC1992 JPEGJPEGCD-ROM

JPEGCPU

Sequential (line by line) and progressive (successive refinement of the whole image) decoding should both be possible. A lossless, hierarchical coding of the same image with different resolutions should also be possible.The user can select parameters to trade off the quality of the reproduced image, the compression processing time, the size of the compressed image.

The encoded data stream has a fixed interchange formatencoded image datathe chosen parameterstables of the coding process.

DCT

JPEG ModesThe lossy, sequential DCT-based mode (baseline process, base mode)The expanded lossy, DCT-based modeThe lossless modeThe hierarchical mode

10:1--100:1 (40:1)25 JPEG 30:1 1000K33K 1MB

2 An image consists of at least one and at most N=255 components or planes.

Each component is a rectangular array XiYi of pixels (the samples).

The resolution of the individual components may be different.

Each pixel is represented by p bits with values in the range from 0 to 2 p1.All pixels of all components of an image must have the same number of bits.The lossy modes of JPEG use a precision of either 8 or 12 bits per pixel.The lossless modes can use between 2 and 12 bits per pixel. With any other number of bits, the application must suitably transform the image.

The compressed data includes:X (maximum of all Xi)Y (maximum of all Yi)factors Hi and Vi for each plane.Hi : relative horizontal resolutionVi : relative vertical resolution P100

the image is divided into data unitsThe lossless mode uses one pixel as one data unit. The lossy mode uses blocks of 88 pixels.Non-interleaved data ordering

Interleaved data ordering

Interleaved data units of different components are combined into Minimum Coded Units (MCU).

According to the JPEG standarda maximum of four components can be encoded using the interleaved mode. Each MCU can contain at most ten data units.Within an image, some components can be encoded in the interleaved mode and others in the noninterleaved mode.

3 DCT

After image preparation, the uncompressed image samples are grouped into data units of 88 pixelsIn this baseline mode, each sample is encoded using p=8bit. Each pixel is an integer in the range 0 to 255.

Example of DCT and IDCT

DCTDCTPT

The pixel values are shifted into the zero-centered interval (128, 127). 128This transformation must be carried out 64 times per data unit. The result is 64 coefficients. DCT8888

Ti=0,j=0DCACij

DCT88DCT

640480640480,8060JPEG88

88 T

PACAC0PT0ACAC0PAC0ACAC

DCTDCT

88DCT(DCT)

JPEG64DCT() (,)T(,)(,)

T(,)(,)(,)

IDCT

JPEGJPEGYCrCb YCrCb YYCrCb YCrCb .JPEG

JPEGYCrCb YCrCb YYYCrCb YYCrCb JPEG10-310-4JPEG

1-255DCT

DC JPEGDCDPCM()88DC

AC T63(AC)6363(Zig-Zag)Z

ZRLEZ

Z 63AC

DCACentropy codingJPEGDC

For the lossy sequential DCT-based base mode, only Huffman encoding is allowed.In the base mode, two different Huffman tables can be used, one for AC-coefficients and for DC-coefficients.

Example of sequential picture preparation

JPEG

38384 bytes (High quality),11331 bytes (Medium quality), 6968 bytes (Low quality),3687 bytes

JPEGQuality FactorPhotoshop012PhotoPaint2250

maximum medium low 8 3 0 3.7:1 7.1:1 8.8:1

maximum medium low 8 3 0 7.6:1 11.8:1 13.3:1

Factor: 100 Size=326321 bytes Factor: 50 Size=46295 bytes Factor: 25 Size=29360 bytes Factor: 5 Size=9438 bytes

10.6.5 ---JPEG2000 JPEGJPEG88 JPEG JPEG 2000 JPEG JPEG (Discrete Cosine Transform) (Wavelet transform)

JPEG2000 JPEG2000JPEG30%50%JPEG2000JPEG30%50%JPEG2000 JPEGJPEG2000JPEG2000

Progressive Transmission JPEG (Region of Interest) JPEG2000JPEG10%30% JPEG2000JPEG

1910Harr80Stromberg 1984MorletFourier1987MallatMallat

(Wavelet Transformation)Fourier(Mallat)Fourier

48013001InernetCDROM

DSPAnalogDevices/IntelIndeoIndeo

: 22:1

FourierMPEG-4

FourierCTFourier