Color Space Transformations
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Color Models
Color Models Jian Huang CS456 Main Color Spaces • CIE XYZ, xyY • RGB, CMYK • HSV (Munsell, HSL, IHS) • Lab, UVW, YUV, YCrCb, Luv, Differences in Color Spaces • What is the use? For display, editing, computation, compression, …? • Several key (very often conflicting) features may be sought after: – Additive (RGB) or subtractive (CMYK) – Separation of luminance and chromaticity – Equal distance between colors are equally perceivable CIE Standard • CIE: International Commission on Illumination (Comission Internationale de l’Eclairage). • Human perception based standard (1931), established with color matching experiment • Standard observer: a composite of a group of 15 to 20 people CIE Experiment CIE Experiment Result • Three pure light source: R = 700 nm, G = 546 nm, B = 436 nm. CIE Color Space • 3 hypothetical light sources, X, Y, and Z, which yield positive matching curves • Y: roughly corresponds to luminous efficiency characteristic of human eye CIE Color Space CIE xyY Space • Irregular 3D volume shape is difficult to understand • Chromaticity diagram (the same color of the varying intensity, Y, should all end up at the same point) Color Gamut • The range of color representation of a display device RGB (monitors) • The de facto standard The RGB Cube • RGB color space is perceptually non-linear • RGB space is a subset of the colors human can perceive • Con: what is ‘bloody red’ in RGB? CMY(K): printing • Cyan, Magenta, Yellow (Black) – CMY(K) • A subtractive color model dye color absorbs reflects cyan red blue and green magenta green blue and red yellow blue red and green black all none RGB and CMY • Converting between RGB and CMY RGB and CMY HSV • This color model is based on polar coordinates, not Cartesian coordinates. -
Chapter 6 : Color Image Processing
Chapter 6 : Color Image Processing CCU, Taiwan Wen-Nung Lie Color Fundamentals Spectrum that covers visible colors : 400 ~ 700 nm Three basic quantities Radiance : energy that flows from the light source (measured in Watts) Luminance : a measure of energy an observer perceives from a light source (in lumens) Brightness : a subjective descriptor difficult to measure CCU, Taiwan Wen-Nung Lie 6-1 About human eyes Primary colors for standardization blue : 435.8 nm, green : 546.1 nm, red : 700 nm Not all visible colors can be produced by mixing these three primaries in various intensity proportions Cones in human eyes are divided into three sensing categories 65% are sensitive to red light, 33% sensitive to green light, 2% sensitive to blue (but most sensitive) The R, G, and B colors perceived by CCU, Taiwan human eyes cover a range of spectrum Wen-Nung Lie 6-2 Primary and secondary colors of light and pigments Secondary colors of light magenta (R+B), cyan (G+B), yellow (R+G) R+G+B=white Primary colors of pigments magenta, cyan, and yellow M+C+Y=black CCU, Taiwan Wen-Nung Lie 6-3 Chromaticity Hue + saturation = chromaticity hue : an attribute associated with the dominant wavelength or dominant colors perceived by an observer saturation : relative purity or the amount of white light mixed with a hue (the degree of saturation is inversely proportional to the amount of added white light) Color = brightness + chromaticity Tristimulus values (the amount of R, G, and B needed to form any particular color : X, Y, Z trichromatic -
COLOR SPACE MODELS for VIDEO and CHROMA SUBSAMPLING
COLOR SPACE MODELS for VIDEO and CHROMA SUBSAMPLING Color space A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components (e.g. RGB and CMYK are color models). However, a color model with no associated mapping function to an absolute color space is a more or less arbitrary color system with little connection to the requirements of any given application. Adding a certain mapping function between the color model and a certain reference color space results in a definite "footprint" within the reference color space. This "footprint" is known as a gamut, and, in combination with the color model, defines a new color space. For example, Adobe RGB and sRGB are two different absolute color spaces, both based on the RGB model. In the most generic sense of the definition above, color spaces can be defined without the use of a color model. These spaces, such as Pantone, are in effect a given set of names or numbers which are defined by the existence of a corresponding set of physical color swatches. This article focuses on the mathematical model concept. Understanding the concept Most people have heard that a wide range of colors can be created by the primary colors red, blue, and yellow, if working with paints. Those colors then define a color space. We can specify the amount of red color as the X axis, the amount of blue as the Y axis, and the amount of yellow as the Z axis, giving us a three-dimensional space, wherein every possible color has a unique position. -
Cielab Color Space
Gernot Hoffmann CIELab Color Space Contents . Introduction 2 2. Formulas 4 3. Primaries and Matrices 0 4. Gamut Restrictions and Tests 5. Inverse Gamma Correction 2 6. CIE L*=50 3 7. NTSC L*=50 4 8. sRGB L*=/0/.../90/99 5 9. AdobeRGB L*=0/.../90 26 0. ProPhotoRGB L*=0/.../90 35 . 3D Views 44 2. Linear and Standard Nonlinear CIELab 47 3. Human Gamut in CIELab 48 4. Low Chromaticity 49 5. sRGB L*=50 with RGB Numbers 50 6. PostScript Kernels 5 7. Mapping CIELab to xyY 56 8. Number of Different Colors 59 9. HLS-Hue for sRGB in CIELab 60 20. References 62 1.1 Introduction CIE XYZ is an absolute color space (not device dependent). Each visible color has non-negative coordinates X,Y,Z. CIE xyY, the horseshoe diagram as shown below, is a perspective projection of XYZ coordinates onto a plane xy. The luminance is missing. CIELab is a nonlinear transformation of XYZ into coordinates L*,a*,b*. The gamut for any RGB color system is a triangle in the CIE xyY chromaticity diagram, here shown for the CIE primaries, the NTSC primaries, the Rec.709 primaries (which are also valid for sRGB and therefore for many PC monitors) and the non-physical working space ProPhotoRGB. The white points are individually defined for the color spaces. The CIELab color space was intended for equal perceptual differences for equal chan- ges in the coordinates L*,a* and b*. Color differences deltaE are defined as Euclidian distances in CIELab. This document shows color charts in CIELab for several RGB color spaces. -
NEC Multisync® PA311D Wide Gamut Color Critical Display Designed for Photography and Video Production
NEC MultiSync® PA311D Wide gamut color critical display designed for photography and video production 1419058943 High resolution and incredible, predictable color accuracy. The 31” MultiSync PA311D is the ultimate desktop display for applications where precise color is essential. The innovative wide-gamut LED backlight provides 100% coverage of Adobe RGB color space and 98% coverage of DCI-P3, enabling more accurate colors to be displayed on screen. Utilizing a high performance IPS LCD panel and backed by a 4 year warranty with Advanced Exchange, the MultiSync PA311D delivers high quality, accurate images simply and beautifully. Impeccable Image Performance The wide-gamut LED LCD backlight combined with NEC’s exclusive SpectraView Engine deliver precise color in every environment. • True 4K resolution (4096 x 2160) offers a high pixel density • Up to 100% coverage of Adobe RGB color space and 98% coverage of DCI-P3 • 10-bit HDMI and DisplayPort inputs display up to 1.07 billion colors out of a palette of 4.3 trillion colors Ultimate Color Management The sophisticated SpectraView Engine provides extensive, intuitive control over color settings. • MultiProfiler software and on-screen controls provide access to thousands of color gamut, gamma, white point, brightness and contrast combinations • Internal 14-bit 3D lookup tables (LUTs) work with optional SpectraViewII color calibration solution for unparalleled color accuracy A Perfect Fit for Your Workspace A Better Workflow Future-proof connectivity, great ergonomics, and VESA mount Exclusive, -
Xilinx PG014 Logicore IP Ycrcb to RGB Color-Space Converter V6.00.A, Product Guide
LogiCORE IP YCrCb to RGB Color-Space Converter v6.00.a Product Guide PG014 July 25, 2012 Table of Contents SECTION I: SUMMARY IP Facts Chapter 1: Overview Feature Summary. 8 Applications . 9 Licensing and Ordering Information. 9 Chapter 2: Product Specification Standards Compliance . 10 Performance. 10 Resource Utilization. 11 Core Interfaces and Register Space . 13 Chapter 3: Designing with the Core General Design Guidelines . 27 Color-Space Conversion Background . 28 Clock, Enable, and Reset Considerations . 34 System Considerations . 36 Chapter 4: C Model Reference Installation and Directory Structure . 38 Using the C-Model . 40 Input and Output Video Structures . 42 Initializing the Input Video Structure . 43 Compiling with the YCrCb to RGB C-Model . 46 YCrCb to RGB Color-Space Converter v6.00.a www.xilinx.com 2 PG014 July 25, 2012 SECTION II: VIVADO DESIGN SUITE Chapter 5: Customizing and Generating the Core Graphical User Interface . 49 Output Generation. 53 Chapter 6: Constraining the Core Required Constraints . 54 Device, Package, and Speed Grade Selections. 54 Clock Frequencies . 54 Clock Management . 54 Clock Placement. 54 Banking . 55 Transceiver Placement . 55 I/O Standard and Placement. 55 SECTION III: ISE DESIGN SUITE Chapter 7: Customizing and Generating the Core Graphical User Interface . 57 Parameter Values in the XCO File . 61 Output Generation. 62 Chapter 8: Constraining the Core Required Constraints . 63 Device, Package, and Speed Grade Selections. 63 Clock Frequencies . 63 Clock Management . 63 Clock Placement. 63 Banking . 64 Transceiver Placement . 64 I/O Standard and Placement. 64 Chapter 9: Detailed Example Design Demonstration Test Bench . 65 Test Bench Structure . -
Preparing Images for Delivery
TECHNICAL PAPER Preparing Images for Delivery TABLE OF CONTENTS So, you’ve done a great job for your client. You’ve created a nice image that you both 2 How to prepare RGB files for CMYK agree meets the requirements of the layout. Now what do you do? You deliver it (so you 4 Soft proofing and gamut warning can bill it!). But, in this digital age, how you prepare an image for delivery can make or 13 Final image sizing break the final reproduction. Guess who will get the blame if the image’s reproduction is less than satisfactory? Do you even need to guess? 15 Image sharpening 19 Converting to CMYK What should photographers do to ensure that their images reproduce well in print? 21 What about providing RGB files? Take some precautions and learn the lingo so you can communicate, because a lack of crystal-clear communication is at the root of most every problem on press. 24 The proof 26 Marking your territory It should be no surprise that knowing what the client needs is a requirement of pro- 27 File formats for delivery fessional photographers. But does that mean a photographer in the digital age must become a prepress expert? Kind of—if only to know exactly what to supply your clients. 32 Check list for file delivery 32 Additional resources There are two perfectly legitimate approaches to the problem of supplying digital files for reproduction. One approach is to supply RGB files, and the other is to take responsibility for supplying CMYK files. Either approach is valid, each with positives and negatives. -
Chapter 2 Fundamentals of Digital Imaging
Chapter 2 Fundamentals of Digital Imaging Part 4 Color Representation © 2016 Pearson Education, Inc., Hoboken, 1 NJ. All rights reserved. In this lecture, you will find answers to these questions • What is RGB color model and how does it represent colors? • What is CMY color model and how does it represent colors? • What is HSB color model and how does it represent colors? • What is color gamut? What does out-of-gamut mean? • Why can't the colors on a printout match exactly what you see on screen? © 2016 Pearson Education, Inc., Hoboken, 2 NJ. All rights reserved. Color Models • Used to describe colors numerically, usually in terms of varying amounts of primary colors. • Common color models: – RGB – CMYK – HSB – CIE and their variants. © 2016 Pearson Education, Inc., Hoboken, 3 NJ. All rights reserved. RGB Color Model • Primary colors: – red – green – blue • Additive Color System © 2016 Pearson Education, Inc., Hoboken, 4 NJ. All rights reserved. Additive Color System © 2016 Pearson Education, Inc., Hoboken, 5 NJ. All rights reserved. Additive Color System of RGB • Full intensities of red + green + blue = white • Full intensities of red + green = yellow • Full intensities of green + blue = cyan • Full intensities of red + blue = magenta • Zero intensities of red , green , and blue = black • Same intensities of red , green , and blue = some kind of gray © 2016 Pearson Education, Inc., Hoboken, 6 NJ. All rights reserved. Color Display From a standard CRT monitor screen © 2016 Pearson Education, Inc., Hoboken, 7 NJ. All rights reserved. Color Display From a SONY Trinitron monitor screen © 2016 Pearson Education, Inc., Hoboken, 8 NJ. -
Dalmatian's Definitions
T H E B L A C K & W H I T E P A P E R S D A L M A T I A N ’ S D E F I N I T I O N S 8 BIT A bit is the possible number of colors or tones assigned to each pixel. In 8 bit files, 1 of 256 tones is assigned to each pixel. 8-bit Jpeg is the default setting for most cameras; whenever possible set the camera to RAW capture for the best image capture possible. 16 BIT A bit is the possible number of colors or tones assigned to each pixel. In 16 bit files, 1 of 65,536 tones are assigned to each pixel. 16 bit files have the greatest range of tonalities and a more realistic interpretation of continuous tone. Note the increase in tonalities from 8 bit to 16 bit. If your aim is the quality of the image, then 16 bit is a must. ADOBE 1998 COLOR SPACE Adobe ‘98 is the preferred RGB color space that places the captured and therefore printable colors within larger parameters, rendering approximately 50% the visible color space of the human eye. Whenever possible, change the camera’s default sRGB setting to Adobe 1998 in order to increase available color capture. Whenever possible change this setting to Adobe 1998 in order to increase available color capture. When an image is captured in sRGB, it is best to leave the color space unchanged so color rendering is unaffected. ARCHIVAL Archival materials are those with a neutral pH balance that will not degrade over time and are resistant to UV fading. -
Specification of Srgb
How to interpret the sRGB color space (specified in IEC 61966-2-1) for ICC profiles A. Key sRGB color space specifications (see IEC 61966-2-1 https://webstore.iec.ch/publication/6168 for more information). 1. Chromaticity co-ordinates of primaries: R: x = 0.64, y = 0.33, z = 0.03; G: x = 0.30, y = 0.60, z = 0.10; B: x = 0.15, y = 0.06, z = 0.79. Note: These are defined in ITU-R BT.709 (the television standard for HDTV capture). 2. Reference display‘Gamma’: Approximately 2.2 (see precise specification of color component transfer function below). 3. Reference display white point chromaticity: x = 0.3127, y = 0.3290, z = 0.3583 (equivalent to the chromaticity of CIE Illuminant D65). 4. Reference display white point luminance: 80 cd/m2 (includes veiling glare). Note: The reference display white point tristimulus values are: Xabs = 76.04, Yabs = 80, Zabs = 87.12. 5. Reference veiling glare luminance: 0.2 cd/m2 (this is the reference viewer-observed black point luminance). Note: The reference viewer-observed black point tristimulus values are assumed to be: Xabs = 0.1901, Yabs = 0.2, Zabs = 0.2178. These values are not specified in IEC 61966-2-1, and are an additional interpretation provided in this document. 6. Tristimulus value normalization: The CIE 1931 XYZ values are scaled from 0.0 to 1.0. Note: The following scaling equations can be used. These equations are not provided in IEC 61966-2-1, and are an additional interpretation provided in this document. 76.04 X abs 0.1901 XN = = 0.0125313 (Xabs – 0.1901) 80 76.04 0.1901 Yabs 0.2 YN = = 0.0125313 (Yabs – 0.2) 80 0.2 87.12 Zabs 0.2178 ZN = = 0.0125313 (Zabs – 0.2178) 80 87.12 0.2178 7. -
Computational RYB Color Model and Its Applications
IIEEJ Transactions on Image Electronics and Visual Computing Vol.5 No.2 (2017) -- Special Issue on Application-Based Image Processing Technologies -- Computational RYB Color Model and its Applications Junichi SUGITA† (Member), Tokiichiro TAKAHASHI†† (Member) †Tokyo Healthcare University, ††Tokyo Denki University/UEI Research <Summary> The red-yellow-blue (RYB) color model is a subtractive model based on pigment color mixing and is widely used in art education. In the RYB color model, red, yellow, and blue are defined as the primary colors. In this study, we apply this model to computers by formulating a conversion between the red-green-blue (RGB) and RYB color spaces. In addition, we present a class of compositing methods in the RYB color space. Moreover, we prescribe the appropriate uses of these compo- siting methods in different situations. By using RYB color compositing, paint-like compositing can be easily achieved. We also verified the effectiveness of our proposed method by using several experiments and demonstrated its application on the basis of RYB color compositing. Keywords: RYB, RGB, CMY(K), color model, color space, color compositing man perception system and computer displays, most com- 1. Introduction puter applications use the red-green-blue (RGB) color mod- Most people have had the experience of creating an arbi- el3); however, this model is not comprehensible for many trary color by mixing different color pigments on a palette or people who not trained in the RGB color model because of a canvas. The red-yellow-blue (RYB) color model proposed its use of additive color mixing. As shown in Fig. -
HD-SDI, HDMI, and Tempus Fugit
TECHNICALL Y SPEAKING... By Steve Somers, Vice President of Engineering HD-SDI, HDMI, and Tempus Fugit D-SDI (high definition serial digital interface) and HDMI (high definition multimedia interface) Hversion 1.3 are receiving considerable attention these days. “These days” really moved ahead rapidly now that I recall writing in this column on HD-SDI just one year ago. And, exactly two years ago the topic was DVI and HDMI. To be predictably trite, it seems like just yesterday. As with all things digital, there is much change and much to talk about. HD-SDI Redux difference channels suffice with one-half 372M spreads out the image information The HD-SDI is the 1.5 Gbps backbone the sample rate at 37.125 MHz, the ‘2s’ between the two channels to distribute of uncompressed high definition video in 4:2:2. This format is sufficient for high the data payload. Odd-numbered lines conveyance within the professional HD definition television. But, its robustness map to link A and even-numbered lines production environment. It’s been around and simplicity is pressing it into the higher map to link B. Table 1 indicates the since about 1996 and is quite literally the bandwidth demands of digital cinema and organization of 4:2:2, 4:4:4, and 4:4:4:4 savior of high definition interfacing and other uses like 12-bit, 4096 level signal data with respect to the available frame delivery at modest cost over medium-haul formats, refresh rates above 30 frames per rates. distances using RG-6 style video coax.