Image formats - fit.vutbr.czibarina/pub/image-formats-en.pdf · Image formats DavidBařina...

Image formats

David Bařina

March 22, 2013

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Contents

1 Notions

2 Uncompressed formats

3 Lossless formats

4 Lossy formats

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Introduction

the need for compression: FullHD image with resolution1920×1080×3 ≈ 6MBcompression: none, lossless, lossyformats: BMP, TIFF, GIF, PNG, JPEG-LS, JPEG, JPEG-2000, . . .

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Compression

data (BMP, TIFF)data → RLE (BMP, TGA, TIFF)data → prediction → context EC (JPEG-LS)data → prediction → RLE → ECdata → prediction → dictionary method (PNG)data → dictionary method (GIF)data → transform → RLE+EC (JPEG)data → transform → context EC (JPEG 2000)

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Color

colorprimary colors of CRTs: R, G, BluminanceITU-R BT.601

Y = 0.299R + 0.587G + 0.114B

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Color models and spaces

modelCIE xy chromaticity diagramspace, gamut

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YCbCrRGB transform

YCbCr

=

0128128

+

+0.299 +0.587 +0.114−0.16875 −0.33126 +0.5+0.5 −0.41869 −0.08131

·R

GB

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Chroma subsampling

Y vs. Cb, Cr

unobservable by humanblock, macropixelJ:a:b, 4:4:4, 4:2:2, 4:1:1, 4:2:0centroids

4:4:4 4:2:2

4:1:1 4:2:0

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Pixelformat

model + memory layoutRGB24 vs. BGR24planar: R0R1R2 . . .G0G1G2 . . .B0B1B2 . . .

packed: R0G0B0R1G1B1 . . .

...{pixel

} row

framebuffer:

image

byte

stride

width

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Multidimensional data

linearizationraster scan (everywhere), zig-zag (JPEG), z-curve (EZW, SPIHT),other (EBCOT)

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Predictorsprediction of symbol x , min. errorpredictor order, domainlinear and non-linear predictors

xa

bc d

a

cb

x

p = a + b − c

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Predictorstrivial: a, b, c, daverage, medianp (fit plane)MED (JPEG-LS)

x̂ =

min(a, b) : c ≥ max(a, b)max(a, b) : c ≤ min(a, b)p

Paeth (PNG)

x̂ = argminx∈a,b,c

|p − x |

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Transforms

sparse image reprezentationlossy methods (quantization)often DCT, DWTblocks, blocking artifacts

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DCT (discrete cosine transform)

gk,j [n,m] = λkλj2N cos

[kπN

(n +

12

)]cos

[ jπN

(m +

12

)]

c[k, j] =N−1∑n=0

N−1∑m=0

f [n,m] gk,j [n,m]

f [n,m] =N−1∑k=0

N−1∑j=0

c[k, j] gk,j [n,m]

0 ≤ k, j < N λk =

{1/√2 : k = 0

1

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DCT (discrete cosine transform)

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DWT (discrete wavelet transform)

aj+1 = (aj ∗ h) ↓ 2

dj+1 = (aj ∗ g) ↓ 2

1st level 2nd level

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2-D DWT

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BMP

BMP (DIB)uncompressed, RLE for palettestores: 1, 4, 8-bit indices intopallete; 16, 24, 32 RGB (BGRorder)bottom-top row order, 32-bitalignedWindows API, MSDNstructures BITMAPFILEHEADER(header, data offset),BITMAPINFOHEADER(dimensions, compression)

BMP file

BITMAPFILEHEADER

BITMAPINFO

image data

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TIFF

TIFF (Tagged Image FileFormat), 1986, 1992, Adobeseveral pages, fragmented data,transparency, colorometrycompression: RLE, LZW, JPEGstructure: analogy to FSheader, IFD, entry, tag,type+count, datatypes: byte (8-bit), ascii(characters), short (16), long(32), . . .

directory(IFD)

header entry

data

nextdirectory

.

.

.

.

.

.

tag

nextentry.

.

.

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TIFF

tags: Compression (none, PackBits, LZW, JPEG), ImageLength,ImageWidth, BitsPerSample, ColorMap, SamplesPerPixel

fragmentation: stripes, tilesstores: bi-level (2), gray-scale (16, 256), palette (16, 256), RGB(16M), CMYK (232), YCbCr (224)more tags: Artist (image creator), Copyright, DateTime,ImageDescription, Make (device manufacturer), Model (devicemodel), Orientation, Software, . . .PackBits: RLE variant, per bytes

I read nI 0 to 127: copy next n + 1 bytes to outputI −127 to −1: output next byte (−n + 1) times

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GIFGIF (Graphics Interchange Format), CompuServe, 1987 (GIF87a),1989 (GIF89a)LZW (patents, PNG)stores: frames (palette with indices up to 8-bits), animations, TrueColor (16M)transparent pixels (89a)logical screen, frames, background color

1

2

3

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GIF

global and local color palletesLZW: clear code, EOFcompression per rowsprogressive transfer: stripes of 8 rows, 4 passes

row sequentially pass of interleaving row by interleaving1 1 12 4 53 3 34 4 65 2 26 4 77 3 48 4 8

Google for: true color gif

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PNG

PNG (Portable Network Graphics), replacement for GIFDeflateextensible, interleaving, alpha channel

pixel type channels bit-depthspalette indices 1, 2, 4, 8grayscale Y 1, 2, 4, 8, 16grayscale w. transparency Y, A 8, 16true color R, G, B 8, 16true color w. transparency R, G, B, A 8, 16

compression: predictor (filter) + Deflate

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PNG

prediction: per rows, per bytes, 5 predictors

predictor predicted valuenone 0left btop aavg. b(a + b)/2cPaeth (above)

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PNGinterleaving: Adam7 (8× 8 pixels, 7 passes, each pass doubleresolution)

1 6 4 6 2 6 4 67 7 7 7 7 7 7 75 6 5 6 5 6 5 67 7 7 7 7 7 7 73 6 4 6 3 6 4 67 7 7 7 7 7 7 75 6 5 6 5 6 5 67 7 7 7 7 7 7 7

structure: blocks (type, size) – critical and ancillaryblock: size, name, data, CRCname: four characters (critical, registered, –, do not copy)critical: IHDR (header), PLTE (palette), IDAT (image data), IEND(footer)

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JPEG-LS

replacement for JPEG (lossless mode), not JPEG modificationbased on LOCO-I (LOw COmplexity LOssless COmpression forImages)predictor + context EC (Rice), also RLE variantcompression on rowsgeneric method, stores e.g. RGB, palette imagesfile format based on JIF (further)

inputimage

compressedimage

contextdetermination

predictionerrorcoding

runcoding

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JPEG-LSgradient D = (D1,D2,D3) (smoothness, edge)

D1 = Rd − RbD2 = Rb − RcD3 = Rc − Ra

chooses compression mode (zero gradient)quantize gradient: Di → Qi ∈ 〈−4, 4〉93 = 729, merge, 365 contexts

xa

bc d

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JPEG-LSMED predictorvalue on edge, or plane fitting

Px =

min(Ra,Rb) : Rc ≥ max(Ra,Rb)max(Ra,Rb) : Rc ≤ min(Ra,Rb)Ra + Rb − Rc

subsequent context dependent correction of predictionnear-lossless method: quantization of prediction error

xa

bc d

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JPEG-LS

codes error of predictionlimited Golomb-Rice code (max. length)parameter of Rice code dependent on contextnegative values mapping

EM =

{2 · |E | : E ≥ 02 · |E | − 1 : E < 0

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JPEG

JPEG committee (Joint Photographic Experts Group), 1992standard ISO/IEC 10918-1, recomendation CCITT/ITU-T T.81incorrectly file format (correctly JFIF or Exif)lossy and lossless compressionsequential and progressive transmissiondefines JIFbaseline process: mandatory, 8-bits, Huffman code with 2 AC + 2 DCtables, sequentialextended process: 8 + 12-bits, 4 AC + 4 DC

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JPEG

DCT quantization

quantizationtable

codetable

RLE Huffmancoder

inputimage

component

compressedbitstream

YCbCr inputchroma subsampling (4:2:2 a 4:2:0)blocks 8× 8, artifactsDCTcoefficients: 1 DC + 63 ACyet fully invertible

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JPEG

DC

(a) Edge direction (b) Frequency (c) Bases

quantization, quantization table (JPEG parametr)

Sqv ,u = round(Sv ,u/Qv ,u)

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JPEG16 11 10 16 124 140 151 16112 12 14 19 126 158 160 15514 13 16 24 140 157 169 15614 17 22 29 151 187 180 16218 22 37 56 168 109 103 17724 35 55 64 181 104 113 19249 64 78 87 103 121 120 10172 92 95 98 112 100 103 199

17 18 24 47 99 99 99 9918 21 26 66 99 99 99 9924 26 56 99 99 99 99 9947 66 99 99 99 99 99 9999 99 99 99 99 99 99 9999 99 99 99 99 99 99 9999 99 99 99 99 99 99 9999 99 99 99 99 99 99 99

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JPEGblocking artifacts

zig-zag linearization, more zeros at the end, EOBDC differentiallyAC using RLE of leading zerosfollowed by arithmetic or Huffman coding (5–10%)Huffman coding: tables for DC and AC coefficients

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JPEG15+ zeros using ZRLAC/DC code = Huffman code (tables) + extra bitsHuffman code cannot consist of only 1-bitscode tables indexing

I DC: categoryI AC: category + zero run length

category range0 01 −1, 12 −3,−2, 2, 33 −7 · · · − 4, 4 . . . 74 −15 · · · − 8, 8 . . . 155 −31 · · · − 16, 16 . . . 31

. . .10 −1023 · · · − 512, 512 . . . 102311 −2047 · · · − 1024, 1024 . . . 2047

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JPEG

JIF, JFIF, Exif, SPIFFbitstream, big endianconsists of segments, max. 65 535Bsegment preceded by marker 0xff + 0x01 až 0xfe

markers: APP0 (JFIF header), APP1 (Exif), SOF0 (image in baselineprocess), SOS (compressed data), RSTm (restart points), DHT(Huffman tables), DQT (quantization tables)JIF extended to JFIF and Exif (incompatible), JFIF+Exifthumbnails, metadata (device model)Exif: TIFF (thumbnail in JFIF)SPIFF not used

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JPEG 2000

successor of JPEGmany improvements, better quality at the same compression ratio,more computationally demandinglossy and lossless compressionofficially ISO/IEC 15444-1, ITU-T T.800based on DWT

preprocessing DWT quantization

ROI

EBCOT

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JPEG 2000color model transform using RCT, ICT

Yr =

⌊R + 2G + B4

⌋Cb = B − GCr = R − G

divison into tiles (blocking artifact)DWT (CDF 9/7, 5/3)

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JPEG 2000

tiles

image

DWT

LL HL

LH HH

LH HH

precinct

codeblock

EBCOT

layers packetsbitstream

decomposition level, resolution, subbands (LL, HL, LH, HH)quantization, ROI (Maxshift)precinct, code-block, EBCOTlayer (quality), packet, bitstream

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JPEG 2000

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JPEG 2000EBCOT

profile-0: code blocks of size of 32× 32 or 64× 64bit-planes from MSB to LSBbits per stripes (4 bits tall)

three passes: significance propagation, magnitude refinement, cleanupcontext AC, 8-bits context

D V D

H X H

D V D

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JPEG 2000

packets: component, tile, resolution, precinct, layer4 axes of progressive transmission: quality, color component,resolution, positionorder can be changedbitstream compatible to JIF, but other markersJP2 file formatmetadata in XML (e.g. XMP)

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JPEG 2000

Comparison with JPEG (108:1, ImageMagick)

Figure: original, JPEG 2000, JPEG

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JPEG 2000

Error resilience

Figure: JPEG, JPEG 2000

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JPEG 2000

Progressive transmission (resolution)

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JPEG 2000

Progressive transmission (quality)

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JPEG 2000

Progressive transmission (position)

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JPEG 2000

Progressive transmission (components)

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Summary

colors, predictorsBMP: uncompressed, RLE for palette imagesTIFF: directory structure, tags, LZW, RLE, JPEGGIF: LZW, 256 colors, 16M colorsPNG: Deflate, predictorsJPEG-LS: context, predictor, Golomb-Rice codesJPEG: YCbCr, DCT, RLE, Huffman code, JIF, segments, markers,JFIF, ExifJPEG 2000: DWT, EBCOT

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