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MATCHSLIDE : INT contribution
Patrick HORAIN Hichem ATTI Waheb LARBI Presented as : "TELESLIDE: Technical aspects ", Jacques Klossa & Patrick Horain, Joint Congress of Quantitative Analytical Cellular Pathology ans Telepathology , September , Heraclion, Crete.
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Wide fields : some issues
Acquisition : A microscope can see only a small field in a slide Browsing wide fields : Narrow band networks Narrow computer screens
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Wide field acquisition
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Mosaicing Grab neighbour fields images and merge (mosaic) them into a wide field image Ex.: 16 images, 1300 1030 pixels 1 image, 4662 3675 pixels Shading ! Mosaicing = assembling individual slide parts into a single image or wide field. Problem: illumination inhomogeneities
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Shading : what ? Problems : Example empty slide :
Illumination inhomogeneities Dust in optical system Example empty slide : original stretched histogram
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Shading correction / single field
Normalise each pixel with illumination / =
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Shading correction / wide field
With shading correction Without shading correction Comparer les 2 images par des allers-et-retours au clavier (touches page suivante / précédente).
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Other issues Future work includes : color correction
robust slides registration for mosaicing hierarchical RoI definition by image analysis
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Wide field browsing
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Browsing requirements
Narrow band networks Use better compression Use progressive transmission Use regions of interest Narrow computer screens Use interactive windowing while loading Use the new JPEG 2000 standard
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What is JPEG 2000 ? New ISO Image compression Standard Wavelet-based
Lossless or lossy compression Better low bit-rate performance than JPEG Progressive transmission by pixel accuracy and resolution Random code stream access and processing Interactive zooming and regions of interest
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JPEG 2000 : wavelets Discrete wavelets transform (DWT)
recursive image decomposition into frequency subbands At each level of the DWT, the low frequency component (upper left) is subsampled by a factor 2 in each direction.
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JPEG 2000 versus JPEG JPEG2000 (0.099 bpp) Original (24 bpp)
DWT integrates a spatial and frequency representation of images without the blocks effect of DCT. At low bit rates, less image degradation with JPEG 2000 than with JPEG. JPEG2000 (0.099 bpp) Original (24 bpp) JPEG (0.18 bpp) DCT used in JPEG involves a decomposition of images on a base of cosine functions with infinite support. Keeping the details local in images is achieved by splitting images to small blocks, which introduces artefacts visible at high compression.
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Progressive transmission : resolution levels
Resolution 5 : 1300 1030 pixels (100 % of image data) Resolution 4 : 650 515 pixels (25 % of image data) Resolution 3 : 325 258 pixels (6.25% of image data) Resolution 2 : 163 129 pixels (1.61 % of data) Resolution 1 : 82 65 pixels (0.45% data)
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Progressive transmission : quality layers
Progression on the precision of the DWT coefficients 1rst layer : 12 kb (7.36 % of image data) 15th layer : 27 kb (16.6 % of image data) 20th layer : 163 kb (100 % of image data) 5th layer : 14.9 kb (9.14 % of image data) 10th layer : 18.1 kb (11.1 % of image data) Optimised rate allocation control on code blocks
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Progressive transmission : other modes
Progression modes : R : Resolution (DWT levels) L : Quality Layers C : Components P: Position 5 std progression orders (apply from right to left) : LRCP, RLCP, RPCL, PCRL, CPRL
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The difference between the progression orders can be perceived only at very high compression rates (< 1 bit per pixel). LRCP is the default progression order : for each L // quality layer for each R // resolution for each C // component for each P // position along lines & columns In the 2 rightmost columns, progression on components (luminance first, then chrominance) is apparent.
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Regions of interest (RoI)
RoI can be coded with different fidelity ex.: lossless RoI vs. lossy background RoI = a rectangle or an arbitrary mask RoI data transmitted before background
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RoI as a rectangle
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RoI as an arbitrary mask
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Progressive transmission with RoI
0.399 bpp 1.133 bpp
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Other issues Future work includes :
comparative evaluation of the progression modes w. r. to our target application automatic RoI selection by image analysis compression and interaction on multiple focus images
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