colour (ترکیب و کاربرد رنگ)

colour (ترکیب و کاربرد رنگ)

اسلاید 1: ColourCPSC 533CFebruary 3, 2003Rod McFarland

اسلاید 2: Ware, Chapter 4The science of colour visionColour measurement systems and standardsOpponent process theoryApplications

اسلاید 3: The science of colour visionReceptors and trichromacy theoryRed Blue Green 

اسلاید 4: Colour measurement systems and standardsAny colour can be matched using a combination of three “primaries”. The primaries are not necessarily red, green, and blue. Any three different colours can be used. The range of colours that can be produced from a given set of primaries is the gamut.

اسلاید 5: Colour standardsCIE (Commission Internationale d’Éclairage)Primaries chosen for mathematical properties: do not actually correspond to colours. These “virtual” colours X, Y, and Z are called tristimulus values.Y is the same as luminance

اسلاید 6: CIE – ChromaticityChromaticity is derived from tristimulus values: Since x+y+z=1, just use x, y values and luminance (Y).Chromaticity diagram:

اسلاید 7: Uniform Colour Space - CIEluvUniform colour space: a representation where equal distances in space correspond to equal distances in perceptionUseful for:Specification of colour tolerancesColor coding (maximum distinction)Pseudocolour sequences to represent ordered data valuesCIE XYZ color space is not uniformCIEluv is a transformation of the chromaticity diagram

اسلاید 8: CIEluv does not solve all problems:Contrast effectsSmall colour patches: difficult to distinguish colours in the yellow-blue direction

اسلاید 9: Opponent process theoryBlack-white (luminance), red-green, and blue-yellow opponentsHas basis in biology and cultureShould use opponent colours for coding data

اسلاید 10: Properties of Colour ChannelsIsoluminant / Equiluminous patterns: a colour pattern whose components do not differ in luminanceRed-green and yellow-blue channels carry only about 1/3 of the detail carried by black-white.

اسلاید 11: Yellow Text on a Blue BackgroundIs fairly easy to read unless the text is isoluminant with the background colour. As the luminance of the background becomes the same as the luminance of the text, it is very difficult to make out what the text says. So much so, that at this point I can write just about anything I want here and hardly anyone would want to put in the effort to see what it was I had written.

اسلاید 12: Other isoluminance effectsStereoscopic depth is not detectable with isoluminant coloursIsoluminance in animation makes it appear to be slower than the same animation in black-and-whiteShape and form are best shown using luminance:

اسلاید 13: Colour appearanceContrastSaturationBrownlowhigh

اسلاید 14: ApplicationsColour selection interfacesColour namingNatural Colour System (NCS) e.g. 0030-G80Y20 Blackness 00, intensity 30, green 80, yellow 20Pantone, Munsell: standard colour chips

اسلاید 15: ApplicationsColour for labelling (nominal information encoding)DistinctnessA rapidly distinguished colour lies outside the convex polygon defined by the other colours in CIE space

اسلاید 16: ApplicationsColour for labelling (2)Unique hues: “universally recognized” hues (red, green, blue, yellow, black, white) should be used Contrast with background: border around objects

اسلاید 17: ApplicationsColour for labelling (3)Colour blindness: majority of colour-blind people cannot distinguish red-green, but most people can distinguish blue-yellow Number: only 5-10 codes easily distinguished

اسلاید 18: ApplicationsColour for labelling (4)SizeColour-coded objects should not be very small (about ½ degree minimum size).Smaller objects should be more highly saturated, large colour-coded regions should have low saturation. Text highlighting should be high-luminance, low-saturation.ConventionsCommon usage of colours, e.g. red=stop, green=ready, blue=cold…

اسلاید 19: ApplicationsColour for labelling (5)Ware’s 12 recommended colours (in order of preference):

اسلاید 20: ApplicationsPseudocolour sequences for mappingPseudocolouring is the practice of assigning colour to map values that do not represent colourMedical imagingAstronomical imagesMapping nonvisible spectrum information to the visible spectrum (astronomy, infrared images)Gray scale best for showing surface shapeColour best for classification

اسلاید 21: ApplicationsColour for mapping (2)For orderable sequences, black-white, red-green, blue-yellow, or saturation (dull-vivid) sequence can be used.For detailed data, the sequence should be based mainly on luminance. For low letail, chromatic or saturation sequences can be used.Uniform colour spaces can be used to create colour sequences where equal perceptual steps correspond to equal metric steps.Where it is important to be able to read off values from a colour map, a sequence that cycles through many colours is preferable.

اسلاید 22: ApplicationsColour for mapping (3)A “spiral” through colour space (cycling through several colours while continuously increasing in luminance) is often a good choice.Hue 0, 50,…250, 45, 95…Luminance 0, 25, 50… 225

اسلاید 23: ApplicationsColour for mapping (4)Perception: even if the sequence is smooth, people tend to see discrete colours, potentially miscategorizing data.My personal division into blue, green, yellow, orange, red, purple: very nonlinear

اسلاید 24: ApplicationsColour for mapping (5)Using colour for 3-D information mappingDifficult to read accuratelyMay be used to identify regionsSatellite images: regions of invisible spectrum mapped to red, green, blue channels

اسلاید 25: ApplicationsColour for multidimensional discrete data5-D plot using (x, y) position, red, green, bluePossible to identify clustersAmbiguous: is a point low-red or high-green?Other methods needed to analyze clusters once identified

اسلاید 26: Rogowitz et al. How Not to Lie with VisualizationVisual representation of data affects the perceived structure of the data.

اسلاید 27: Enhancing data interpretation using ColourPerceptual impact of a colour is not predictable from the red/green/blue components of the colourMapping different aspects of colour to different data is not intuitively decodable by users.Default colour maps: rainbowPerceptual nonlinearityFalse contoursYellow attracts attention

اسلاید 28: Guiding colour map selectionConstrain the set of colour maps available to the user based on:Data typeData spatial frequencyVisualization taskOther design choices made by user

اسلاید 29: Representing StructureNominal dataObject should be distinguishably different but not perceptually orderedOrdinal dataDistinguishable with perceptual orderingInterval dataEqual steps in data correspond to equal steps in perceived magnitudeRatio dataZero point distinguishable in colour sequence

اسلاید 30: StructureMagnitude of a variable at every spatial positionUse luminance (gray scale) or saturation

اسلاید 31: Spatial Frequencyhigh spatial frequency lowluminance-basedsaturation-based

اسلاید 32: SegmentationLow frequency – more segmentation steps can be used

اسلاید 33: HighlightingLuminance-based map can be highlighted using hue variations. The highlighted regions have the same luminance value as the rest of the map.

اسلاید 34: PRAVDAPerceptual Rule-Based Architecture for Visualizing Data Accurately Part of IBM’s Visualization Data Explorer (http://www.research.ibm.com/dx/)Provides choices for colour maps based on spatial frequency, data type, and user-selected goal: isomorphic (structure-preserving), segmentation, highlighting

اسلاید 35: PRAVDA