lect11-jpeg2000

CS 414 - Spring 2014CS 414 Multimedia Systems Design Lecture 11 JPEG 2000Compression

Klara NahrstedtSpring 2014

CS 414 - Spring 2014

CS 414 - Spring 2014Administrative MP1 posted


Todays Discussed Topic JPEG-2000 Compression

Reading: Section 7.5 in Media Coding book, Steinmetz&Nahrstedt, and http://en.wikipedia.org/wiki/JPEG_2000 and links in slides



JPEG Steps Review Image Preparation Components Separation Block Division (8x8 Blocks) of each Component Image Processing Pixel Value Shifting2D DCT Transformation Creation of DC and AC CoefficientsQuantization Quantization TablesEntropy Coding Zig-Zag Ordering DC Coefficients Differential CodingAC Coding - RLE & Huffman CodingCS 414 - Spring 2014


JPEG-2000CS 414 - Spring 2014Original (uncompressed TIF 116KB)

JPEG-2000 (8:1, 14KB)JPEG (8:1, 14KB)http://www.photographical.net/jpeg2000.html


JPEG-2000Created in 2000 by JPEG committeeFile extension: jp2 for ISO/IEC 15444-1 conforming filesimage/jp2 for MIME type



JPEG-2000 FeaturesLow bit rate compression performanceCurrent standards offer excellent rate-distortion performance in mid and high bit ratesLow bit rate distortions become unacceptableLossless and lossy compression Current standard does not provide superior lossless and lossy compression in a single code-streamCS 414 - Spring 2014


JPEG-2000 FeaturesLarge ImagesCurrent standard does not allow for images larger than 64Kx64K pixels without quality degradationSingle decompression architectureCurrent standard has 44 modes (application specific, and not used by majority JPEG coders)Single common decompression architecture can provide greater interchange between applications CS 414 - Spring 2014


JPEG-2000 FeaturesTransmission in noisy environmentCurrent standard has provision for restart intervals, but image degrades badly when bit errors occur.Computer generated imagery (Graphics)Current standard is optimized only for natural imageryCompound documentsCurrent standard is not applied to compound documents because of its poor performance when applied to text imagery CS 414 - Spring 2014


JPEG-2000 FeaturesSuperior low bit rate performance Below 0.25 bits per pixel for highly detailed grey-scale imagesCS 414 - Spring 2014


JPEG-2000 FeaturesLossless and lossy compressionLossless compression uses progressive decoding (i.e., difference image encoding) for medical imagingProgressive transmission by pixel accuracy and resolutionReconstruction of images is possible with different resolutions and pixel accuracy for different target devices



JPEG-2000 FeaturesRandom code-stream access and processingNeeded in case images have parts that are more important than othersUser defines regions-of-interest in the image to be randomly accessed and/or decompressed with less distortion than the rest of images random code-stream processing allows operations: rotation, translation, filtering, feature extraction, scaling,CS 414 - Spring 2014


JPEG-2000 Pipeline CS 414 - Spring 2014

Preprocessing

Discrete Wavelet Transform

Entropy Code

Post-processing

Quantization


Methods of Compression DCT-based coder New baseline JPEG algorithm required for backward compatibility with existing JPEGWavelet-based coder This method permits coding of still images with high coding efficiency as well as spatial and SNR (signal-to-noise ratio) scalability at fine granularity (see also tutorial part1/part2/part3 -http://users.rowan.edu/~polikar/WAVELETS/WTpart1.html)CS 414 - Spring 2014


Image Preprocessing - Color Component TransformationJPEG-2000: transformation from RGB to YCBCR or YUVIrreversible Color Transform:uses the well known YCBCR color space. It is called "irreversible" because it has to be implemented in floating or fix-point and causes round-off errors.Reversible Color Transform:uses a modified YUV color space that does not introduce quantization errors, so it is fully reversible. CS 414 - Spring 2014


Discrete Wavelet TransformDWT (Discrete Wavelet Transform) extracts information from the source image at different scales, locations and orientationsJPEG-2000 uses two techniques in wavelet-based coder 2D wavelets multi-scale transformsWavelet is defined as a set of basic functions, derived from the same prototype functionPrototype function is known as mother waveletExamples: Mexican Hat wavelet, Haar waveletCS 414 - Spring 2014


2D Mexican Hat analyzing waveletTime domainCS 414 - Spring 2014


Example of artifacts produced by wavelet transform (for different scale parameters)CS 414 - Spring 2014


Wavelet Transform PropertiesWavelet transform coders process high and low frequency parts of image independentlyDCT methods have difficulties with high-frequency informationWavelet method transforms image as a whole (not subdivided into pixel blocks)No blocking artifacts occurWavelet coders degrade gracefully



Forward Wavelet Transform CS 414 - Spring 2014 Image is first filtered along the x dimension, resulting in low- pass and high-pass image- Since bandwidth of both low pass and high pass image is now half that of the original image, both filtered images can be down-sampled by factor 2 without loss of information- Then both filtered images are again filtered and down- sampled along the y dimension resulting in four sub-images


Wavelet TransformCS 414 - Spring 2014


Wavelet Transform (1)CS 414 - Spring 2014


Wavelet Transform (2) CS 414 - Spring 2014


JPEG-2000 Resolution ScalabilityCS 414 - Spring 2014Source: http://www.ee.unsw.edu.au/~taubman/seminars_files/IEEE_IEA_J2K.pdf


JPEG-2000 ScalabilityScalable in both SNR and resolutionCS 414 - Spring 2014More bits


Conclusion - Artifacts of JPEG-2000 Compression

Compression 1/20 size is without incurring visible artifacts If artifacts occur they can be seen as Smoothing rather than squares or mosquito noiseCS 414 - Spring 2014


ADDITIONAL SLIDESCS 414 - Spring 2014


JPEG-2000 ScalabilityCS 414 - Spring 2014


JPEG-2000 Performance Gain up to about 20% compression performance to the first JPEG standardApplications of JPEG-2000Large imagesImages with low-contrast edges (e.g., medical imagesIn printers, scanners, facsimileHD satellite imagesCS 414 - Spring 2014


Applications of Motion JPEG2000Leading digital film standard Supported by Digital Cinema Initiatives for storage, distribution and exhibition of motion picturesConsidered by Library of Congress to be the digital archival formatCS 414 - Spring 2014


Available Software Implementation CS 414 - Spring 2014


Available Hardware Implementation CS 414 - Spring 2014


Lytro CameraLytro start-up companyTechnology allows a pictures focus to be adjusted after it is taken. Lytros founder Ren NgLytro camera captures far more light data, from many angles than it is possible with conventional cameraIt accomplishes it with a special sensor called a microlens array, which puts the equivalent of many lenses into a small spaceCS 414 - Spring 2014


**********Search for Wavelet Compression Example*This transform maps image into frequency sub-bands which represent approximation scalesSub-band is a set of coefficients real numbers which represent aspects of the image associated with a certain frequency range as well as a spatial area of image

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lect11-jpeg2000

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