Sunderland, NE England Robert Grosseteste (1175-1253) Bishop of Lincoln Teacher of Francis Bacon Exhibit featuring color ideas of Robert Grosseteste Closes Saturday! Exactly 16 colors: (unnamed) White 7 near-white 7 near-black Black 3/8/18 World of Color 7 1
A World of Color Session 7 Color Recording and Reproduction OLLI at Illinois Spring 2018 D. H. Tracy
Motion Silencing 3/8/18 World of Color 7 3
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Togo 3/8/18 World of Color 7 6
Course Outline 1. Overview, History and Spectra 2. Nature and Sources of Light 3. Eyes and Color Vision 4. Color Spaces and Color Mixing 5. Origins of Colors of Things 6. Visual Perception: Neurons and the Brain 7. Color Recording and Reproduction, Media 8. Color in Arts and Culture, Emotive Aspects 3/8/18 World of Color 7 7
Session 7 Outline Opponent Theory Color Imaging and Reproduction Electronic (cameras, video, movies) Print media 3/8/18 World of Color 7 8
Goethe s woman in red at an Inn Optical Illusion is Optical Truth J. W. Goethe 3/8/18 World of Color 7 9
Chromatic Opponents Hermann von Helmholtz (1821-1894) Ewald Hering (1834-1918) Proponent of Young-Helmholtz-Maxwell Tristimulus Theory In Goethe Tradition Proposed Opponent 4-Color Theory 3/8/18 World of Color 7 10
Questions Asked of Subjects Type A Questions: Objective Answers (e.g. Yes/No) Are these patches different? Type B Questions: Subjective Judgments/Opinions Describe this color. Is it reddish? Is it greenish? 3/8/18 World of Color 7 11
Questions Asked of Subjects Type A Questions: Objective Answers (e.g. Yes/No) What symbol do you see? Type B Questions: Subjective Judgments/Opinions Describe this color. Is it reddish? Is it greenish? 3/8/18 World of Color 7 12
Hering s Unique Colors Particular colors that are described as not containing any of the others Hering claimed these are particular types of Red Green Yellow Blue Unique Red Unique Green Unique Yellow Unique Blue and they form Opponent Pairs Red-Green Blue-Yellow White-Black 3/8/18 World of Color 7 13
Microsoft Office Color Model srgb Gamut 2/22/2018 World of Color 5 14
Approximate Unique Colors 2/22/2018 World of Color 5 15
Typical Unique Colors Pointer s Gamut srgb Blue ~470 nm Green ~ 510 nm Yellow ~ 575nm* Red ~650 nm (but with a little 490 added) Unique Yellow varies with individuals from 565-590nm, but is highly reproducible in each person. 2/22/2018 World of Color 5 16
Typical Unique Colors Blue ~470 nm Green ~ 510 nm Yellow ~ 575nm* Red ~650 nm (but with a little 490 added) Unique Colors do have meaning, and reflect some neurological reality. Almost everyone can learn to find them quickly. Works across cultures Broadly similar locations, but with some variation person to person Very stable in each individual Unique Yellow varies with individuals from 565-590nm, but is highly reproducible in each person. 2/22/2018 World of Color 5 17
Hering Color Wheel Unique Green, e.g. Note that Opponents Yellow and Blue never mix. Ditto for Opponents Green and Red Zero Sum Game Hering: There is a Green-Red Substance : Green is increasing amount of Substance Red is decreasing amount of Substance 3/8/18 World of Color 7 18
How could Tristimulus and Opponency be Reconciled? Early on (1905), it was realized that subtracting tristimulus channels could implement opponency: Green Red or Red-Green Blue - Yellow = Blue (Red+Green) Much later, color opponent ganglion receptive fields were found in the retina (and also in the LGN) 3/8/18 World of Color 7 19
Color Detection Remember the Color Opponent Retinal Ganglion Cells? + + + + + + + + Yellow = R + G 3/1/18 World of Color 6 20
Current Understanding Opponent Ganglion Cell outputs could roughly explain subjective color sensations, but These low level signals are not directly available to higher vision regions They turn out not to produce the right Hering perceptions anyway Where and how we get our subjective color experiences remains unknown 3/8/18 World of Color 7 21
Digital Imaging 101101001 3/8/18 World of Color 7 22
Relative Sensitivity Relative Intenisty Spectrum of Light Reflected from Green Leaf S M L λ 2/15/2018 World of Color 4 23
Relative Intenisty Direct Approach: Measure the Whole Spectrum [every 10 nm, e.g.] ❶ ❷ ❸ ❹ 30 Spectrum of Light Reflected from Green Leaf λ 2/15/2018 World of Color 4 24
Digital Imaging with 30 Spectral Channels [30 intensity values] lots of data! $1 million boxes? This system would do a great job. The color gamut would be complete. It would work for color deficient people, as well as birds, fishes, etc. There would be no color reproduction errors. Projector needs 30 light sources [30 different colors (wavelengths) superimposed on each pixel displayed] 3/8/18 World of Color 7 25
If 30 Channels is too extravagant, what is the minimum number of spectral channels? 3/8/18 World of Color 7 26
If 30 Channels is too extravagant, what is the minimum number of spectral channels? 3 More would be better, but 3 is enough to be useful 3/8/18 World of Color 7 27
If 30 Channels is too extravagant, what is the minimum number of spectral channels? 3 CIE 1931 Chromaticity Diagram 3/8/18 World of Color 7 28
Digital Imaging with 3 Channels Acquire 3 Images: Red Green Blue 101101001 Not the same R, G & B spectra! Display 3 Images: Red Green Blue 3/8/18 World of Color 7 29
Most Common: Liquid Crystal Displays 3/8/18 World of Color 7 30
Show crossed polarizers 3/8/18 World of Color 7 31
3 Chip Liquid Crystal Projector 3/8/18 World of Color 7 32
3 Chip LCD Projector 3/8/18 World of Color 7 33
Organic LED Panel for Cell Phone,Monitor or TV OLED Small colored LEDs actually emit the light 3/8/18 World of Color 7 34
Digital Mirrors 3/8/18 World of Color 7 35
Digital Mirror Projection Micro mirrors in focal plane can reflect light into projection lens, or off to one side, with sub-millisecond timing 3/8/18 World of Color 7 36
Digital Mirror Projection 3/8/18 World of Color 7 37
Digital Mirror Projectors for Video or Cinema 3/8/18 World of Color 7 38
Official Gamut used for Computer Displays and HDTV: srgb Rec 709 Note: Colors shown are not nearly accurate! 3/8/18 World of Color 7 39
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Newer Gamuts DCI-P3 Digital Cinema (+ Some 4K HDTV) srgb, Rec 709 (HDTV, BluRay) Pointer s Gamut 3/8/18 World of Color 7 42
Newer Gamuts Some Cell Phones reach P3 Gamut Apple X Samsung S8 Google Pixel-2XL Some recent 4K HDTVs reach 90% of P3 (WCG) BluRay uses Rec709 [UHD BluRay can use Rec2020] Pointer s Essentially no Gamut Rec2020 equipment available Rec 2020 (Goal for U-HDTV) DCI-P3 Digital Cinema (+ Some 4K HDTV) srgb, Rec 709 (HDTV, BluRay) 3/8/18 World of Color 7 43
Bigger Gamut with 4 Colors: RGB+Yellow Sharp s Aquos QuadColor LCD TV 3/8/18 World of Color 7 44
White Patch Spectra as seen on 2 RGB Display Types Original (roughly) srgb Display P3 Display 3/8/18 World of Color 7 45
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Demo: Compare White Patch Spectra from tungsten lamp, Epson 3LCD Projector, and cell phone OLED display 3/8/18 World of Color 7 47
A bit about color encoding 3/8/18 World of Color 7 48
Luminance is the main element in human vision Color is added in as a bonus 3/1/18 World of Color 6 49
Video Encoding RGB stored as YUV (Y CbCr) R G B Y = Luminance Chroma U Chroma V 3/1/18 World of Color 6 50
Video Encoding RGB stored as YUV (Y CbCr) but video broadcast, stored on BluRay, or streamed on internet to consumers is subsampled! R G B Y = Luminance Chroma U Chroma V 1 in 4 Pixels sent! 1 in 4 Pixels sent! 3/1/18 World of Color 6 51
8 Pixels from Original Scene Same 8 Pixels after Chroma Subsampling Compare! Y (Luma) Chroma Eyes Can t Tell the Difference! 4:4:4 4:2:0 3/1/18 World of Color 6 52
8 Pixels from Original Scene Same 8 Pixels after Chroma Subsampling Compare! Y (Luma) Chroma 4:4:4 Data transmitted: 8 Y Luma values 8 Chroma U values 8 Chroma V values Total: 24 numbers Eyes Can t Tell the Difference! 4:2:0 Data transmitted: 8 Y Luma values 2 Chroma U values 2 Chroma V values Total: 12 numbers 3/1/18 World of Color 6 53
Digital Imaging with 3 Channels Acquire 3 Images: Red Green Blue 101101001 Data Storage Display 3 Images: Red Green Blue 3/8/18 World of Color 7 54
Digital Imaging with 3 Channels Acquire 3 Images: Red Green Blue 101101001 Data Storage Display 3 Images: Red Green Blue 3/8/18 World of Color 7 55
Relative Sensitivity What Should the 3 Camera Channels Be? A logical choice. why not use human Cone responses? S M L Human Cone Responses λ 2/15/2018 World of Color 4 56
Using Cone Responses for 3 Camera Channels allows color and luminosity to be uniquely identified. Display Gamut 2/15/2018 World of Color 4 57
Some Typical Camera Response Curves NIR needs Blocking! 2/15/2018 World of Color 4 58
Using Response from the 3 Camera Channels allows color and luminosity to be only roughly guessed*. Display Gamut * when camera RGB filters differ from human cones 2/15/2018 World of Color 4 59
Building a Camera Sensor (CCD or CMOS) Microlenses with color filters on each sensor pixel Bayer Pattern Doubling up on Green pixels improves luminance spatial resolution 2/15/2018 World of Color 4 60
Sensor (CCD or CMOS) Building a Camera Front and back cell phone cams Bayer Pattern 2/15/2018 World of Color 4 61
Building a Camera Sensor (CCD or CMOS) DSLR Bayer Pattern 2/15/2018 World of Color 4 62
3 Chip Camera Optics: High End Blue Channel Used with CCD sensors, less necessary with newer CMOS sensors Red Channel Glass Prisms Green Filter Green Channel Permits more accurate control of RGB filter profiles, and much higher sensitivity at low light levels. 3/8/18 World of Color 7 63
3-Chip Cameras for Cinematography and Broadcast TV 3/8/18 World of Color 7 64
CMYK Printing on Paper Key Yellow Magenta Cyan White Paper Transparent Inks Have Subtractive Color (8 including White) C M Y K Halftone Dots Rotated Seen from a distance Halftone Dots Allow Lighter, Less Saturated Colors Allows random overlaps of dots 3/8/18 World of Color 7 65
CYMK Halftone Close Up 3/8/18 World of Color 7 66
More Gamuts [Software Bug!] [Consumer Displays] Hexachrome 6-ink Subtractive Printing [Standard 4-ink Printing] Printed Ink Gamuts do not approach saturated spectral locus 3/8/18 World of Color 7 67