2. COMPUTER GRAPHICS CS 482 – FALL 2015 OCTOBER 6, 2015 IMAGE MANIPULATION COMPRESSION COMPOSITING

3. COMPRESSION CS 482 – FALL 2015 JPEG OCTOBER 6, 2015: IMAGE MANIPULATIONPAGE 139 THE JOINT PHOTOGRAPHIC EXPERT GROUP (JPEG), A VIDEO STANDARDS ORGANIZATION, HAS DEVELOPED A TECHNIQUE FOR COMPRESSING STILL IMAGES BY EXPLOITING THE LOCALIZED COHERENCE OF MOST IMAGES. UNCOMPRESS ED COMPRESSED TO 33% COMPRESSED TO 22% COMPRESSED TO 9%

4. COMPRESSION CS 482 – FALL 2015 JPEG’S ZIG-ZAG RUN-LENGTH ENCODING OCTOBER 6, 2015: IMAGE MANIPULATIONPAGE 140 -490 00 -120 00 -160 00 90 00 0 00 0 00 00 00 00 00 0 00 00 00 0 00 00 00 10 00 00 00 00 00 00 00 JPEG USES A ZIGZAG PATTERN TO IMPLEMENT ITS RUN-LENGTH ENCODING OF PIXEL INFORMATION, THUS TAKING ADVANTAGE OF BOTH THE HORIZONTAL AND THE VERTICAL COHERENCE OF MOST IMAGES. STEP 1: SPLIT THE IMAGE INTO ITS RED, GREEN, AND BLUE PLANES. STEP 2: BREAK EACH COLOR PLANE INTO 8X8 BLOCKS OF PIXELS. STEP 3: APPLY DCT TO EACH 8X8 BLOCK. -7840 00 -1640 00 -1640 00 1370 00 -160 00 -210 00 -190 00 00 00 -160 00 -190 00 -210 00 110 00 480 00 -90 00 -90 00 230 00 STEP 4: QUANTIZE THE ARRAY TO REDUCE ITS SIZE IN MEMORY. 1611 1212 1413 1417 1016 1419 1624 2229 2440 2856 4057 5187 5161 6055 6956 8062 1822 2435 4964 7292 3756 5564 7887 9598 68109 81104 103121 112100 10377 11392 120101 10399  -490 00 -120 00 -160 00 90 00 0 00 0 00 00 00 00 00 0 00 00 00 0 00 00 00 10 00 00 00 00 00 00 00 -7840 00 -1640 00 -1640 00 1370 00 -160 00 -210 00 -190 00 00 00 -160 00 -190 00 -210 00 110 00 480 00 -90 00 -90 00 230 00 STEP 5: USE ZIGZAG PATTERN TO YIELD A VECTOR; USE RUN-LENGTH ENCODING TO COMPRESS IT FOR TRANSMITTING. =

5. COMPRESSION CS 482 – FALL 2015 GIF OCTOBER 6, 2015: IMAGE MANIPULATIONPAGE 141 THE GRAPHICS INTERCHANGE FORMAT (GIF) APPLIES LEMPEL-ZIV-WELCH (LZW) COMPRESSION TO AN IMAGE, SEEKING RECURRING SEQUENCES OF COLORS. FOR EXAMPLE, THE FOLLOWING SEQUENCE OF 33 COLORED PIXELS: OCCURS AT SEVERAL PLACES WITHIN THE IMAGE. THE MOST COMMON LENGTHY SEQUENCES ARE REPLACED WITH SPECIAL CODES, POTENTIALLY REDUCING THE IMAGE FILE’S SIZE SIGNIFICANTLY. UNLIKE JPEG, GIF IS A LOSSLESS COMPRESSION TECHNIQUE, BUT IT HAS THE DISADVANTAGE OF ONLY WORKING WITH IMAGES CONTAINING NO MORE THAN 256 DIFFERENT COLORS.

6. COMPRESSION CS 482 – FALL 2015 PNG OCTOBER 6, 2015: IMAGE MANIPULATIONPAGE 142 THE PORTABLE NETWORK GRAPHICS (PNG) STANDARD ATTEMPTS TO USE SPATIAL COHERENCE TO REDUCE THE RANGE OF PIXEL COLOR VALUES BEFORE COMPRESSING. THIS IS ACCOMPLISHED BY SUBTRACTING SOME COMBINATION OF THE COLORS IN THE PIXELS TO THE NORTH, WEST, AND NORTHWEST OF THE PIXEL BEING “FILTERED”. PNG THEN APPLIES A “DEFLATION” ALGORITHM, SIMILAR TO GIF’S LZW ALGORITHM, TO COMPRESS THE MOST COMMON LENGTHY PATTERNS OF COLOR SEQUENCES. FINALLY, PNG COMPRESSES EVEN FURTHER BY APPLYING HUFFMAN ENCODING TO THE RESULTS OF THE DEFLATION.

7. COMPOSITING CS 482 – FALL 2015 FOREGROUND AND BACKGROUND OCTOBER 6, 2015: IMAGE MANIPULATIONPAGE 143 TO COMBINE IMAGES THAT HAVE BEEN RENDERED SEPARATELY, COMPOSITING TECHNIQUES ARE USED. BACKGROUND A MATTE PAINTING OF THE HALLWAY CORRIDOR DOWN WHICH THE ACTUAL ACTOR RAN DURING THE SCENE. REFERENCE SPHERE A CHROME SPHERE IS FILMED ON THE ACTUAL SET IN THE ACTOR’S APPROXIMATE POSITION IN ORDER TO DERIVE LIGHTING DIRECTION. ACTOR THE ACTOR IS FILMED, WITHOUT MAKEUP, CONDUCTIN G THE SCENE.

8. COMPOSITING CS 482 – FALL 2015 ILLUMINATION OCTOBER 6, 2015: IMAGE MANIPULATIONPAGE 144 DIFFUSE REFLECTION COMBINES THE MAIN LIGHT SOURCE AND THE BACK LIGHT TO APPROXIMATE LIGHT BEHAVIOR AS IT HITS MICROSCOPICALLY ROUGH SURFACES. SPECULAR REFLECTION EXPRESSES WETNESS OF CHARACTER’S SKIN BY APPROXIMATING HOW SCENE LIGHT’S WOULD REFLECT OFF A SMOOTH SURFACE.

9. COMPOSITING CS 482 – FALL 2015 MATERIAL PROPERTIES OCTOBER 6, 2015: IMAGE MANIPULATIONPAGE 145 REFLECTION REFLECTION OF THE NON-LIGHT OBJECTS SURROUNDING THE CHARACTER, PERHAPS EVEN INCLUDING CHARACTER SELF- REFLECTION. COLOR THE VARIOUS COMPONENTS OF THE CHARACTER’S BODY HAVE DIFFERENT COLORS MAPPED TO THEM.

10. COMPOSITING CS 482 – FALL 2015 RADIANCE OCTOBER 6, 2015: IMAGE MANIPULATIONPAGE 146 AMBIENT ILLUMINATION THE CONTRIBUTION OF LIGHT BOUNCING AROUND IN ALL DIRECTIONS WITHIN THE CHARACTER’S ENVIRONMENT IS SIMULATED. SUBSURFACE SCATTERING WHEN LIGHT ENTERS A TRANSLUCENT OBJECT (IN THIS CASE, SKIN), IT BOUNCES AROUND SOMEWHAT AND THEN EXITS.

11. COMPOSITING CS 482 – FALL 2015 CAMERA TRICKS OCTOBER 6, 2015: IMAGE MANIPULATIONPAGE 147 Z-DEPTH PASS THE DISTANCE FROM THE CAMERA OF EACH SURFACE POINT IS DETERMINED TO MASK FOR COLOR CORRECTION AND APPLY DEPTH DEFOCUS. FRESNEL REFLECTION HIGHLIGHTS AROUND THE BORDER OF SURFACES ARE ADJUSTED BY DETERMINING THE SURFACE ANGLE WITH RESPECT TO THE CAMERA.

12. COMPOSITING CS 482 – FALL 2015 FINISHING TOUCHES OCTOBER 6, 2015: IMAGE MANIPULATIONPAGE 148 VEIN MATTE VEINS ON THE TORSO, NEAR THE EYES, AND ON THE NECK AND HEAD ARE KEPT IN DIFFERENT CHANNELS TO PROVIDE SEPARATE CONTROL MECHANISMS TO THE ARTIST. FINAL COMPOSITE