Pixelization of Color Images: All Bands Equal

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  Light Departemen Ilmu Komputer -IPB

  16 × Pixelization of Color Images: R, G, & B Bands

  11 September 2008 ^{6 1999-2007 by Richard Alan} _{Peters II}

  Pengantar Pengolahan Citra Digital

  L – downsample factor R – information content Departemen Ilmu Komputer -IPB

  Pixelization of Color Images: All Bands Equal

  11 September 2008 ^{5 1999-2007 by Richard Alan} _{Peters II}

  Pengantar Pengolahan Citra Digital

  The Retina Diagram from http://webvision.med.utah.edu/

  Kuliah 03 – Color Perception Yeni Herdiyeni http://ilkom.fmipa.ipb.ac.id/~yeni/ppcd

  11 September 2008 ^{4 1999-2007 by Richard Alan} _{Peters II}

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  The Retina Diagram from http://webvision.med.utah.edu/

  11 September 2008 ^{3 1999-2007 by Richard Alan} _{Peters II}

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  The Eye Diagram from http://webvision.med.utah.edu/

  11 September 2008 ^{2 1999-2007 by Richard Alan} _{Peters II}

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  L – downsampled band R – information content

• – Luminance Hue Saturation

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  

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  11 September 2008 ^{12 1999-2007 by Richard Alan} _{Peters II}

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  (H+S) Only L – downsample factor R – information content

  16 × Pixelization of Color Images: Chrominance

  11 September 2008 ^{11 1999-2007 by Richard Alan} _{Peters II}

  Pengantar Pengolahan Citra Digital

  L – downsample factor R – information content Departemen Ilmu Komputer -IPB

  16 × Pixelization of Color Images: Luminance Only

  11 September 2008 ^{10 1999-2007 by Richard Alan} _{Peters II}

  11 September 2008 ^{9 1999-2007 by Richard Alan} _{Peters II}

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  HSV (Hue Saturation Value)

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  Luminance (brightness) atau kesilauan; dimensi pengalaman visual yang terkait dengan jumlah cahaya yang dilepaskan atau dipantulkan (intensitas cahaya) oleh sebuah benda Hue adalah dimensi pengalaman visual yang dinyatakan oleh nama-nama warna dan terkait dengan panjang gelombang cahaya Saturation adalah kejelasan atau kemurnian sebuah warna; dimensi pengalaman visual terkait dengan kompleksitas gelombang cahaya , yaitu seberapa lebar atau sempit jangkauan gelombang cahaya. Ketika cahaya mengandung sebuah gelombang tunggal, maka dapat dikatakan bahwa warna murni dan warna yang dihasilkan dapat dikatakan tersaturasi penuh (saturasi sama dengan 1). Dititik ekstrem lainnya adalah cahaya putih yang sepenuhnya tidak tersaturasi) atau saturasinya sama dengan nol.

  11 September 2008 ^{8 1999-2007 by Richard Alan} _{Peters II}

  L H S

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  The brain transforms RGB into separate brightness and color channels (e.g., LHS).

  The eye has 3 types of photoreceptors: sensitive to red, green, or blue light.

  In the Brain: from RGB to LHS lu m in a n ce hue sa tu ra tio n photo receptors brain

  11 September 2008 ^{7 1999-2007 by Richard Alan} _{Peters II}

  L – downsampled band R – information content

• – information content
• – information content … but different visual information.

  2

  4 b ² g ² r ² Color Sensing / Color Perception

  3

  2

  1

  11 September 2008 ^{18 1999-2007 by Richard Alan} _{Peters II}

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  … but the responses of the “green” and “blue” receptors differ …

  4 b ¹ g ₁ r ¹ Color Sensing / Color Perception

  3

  2

  1

  11 September 2008 ^{17 1999-2007 by Richard Alan} _{Peters II}

  4 Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  3

  1

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  Color Sensing / Color Perception Note that the “red” receptor exhibits the same response at 4 different wavelengths …

  11 September 2008 ^{16 1999-2007 by Richard Alan} _{Peters II}

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  Color Sensing / Color Perception These are approximations of the responses to the visible spectrum of the “red”, “green”, and “blue” receptors of a typical human eye.

  11 September 2008 ^{15 1999-2007 by Richard Alan} _{Peters II}

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  L – downsampled band R

  

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  11 September 2008 ^{14 1999-2007 by Richard Alan} _{Peters II}

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  These 4 images all have the same amount of digital information…

  L – downsampled band R

  16 × Pi xel iz a ti o n

  11 September 2008 ^{13 1999-2007 by Richard Alan} _{Peters II}

  … at each of the 4 locations so that …

  Pengantar Pengolahan Citra Digital Pengantar Pengolahan Citra Digital Departemen Ilmu Komputer -IPB Departemen Ilmu Komputer -IPB

  Color Sensing / Color Perception Color Sensing / Color Perception … each of the 4 wavelengths

  1

  2

  3

  4

  1

  2

  3

  4 is represented by a unique response from the set of 3 receptors. g ₃ r ₃ r ₄ g ⁴ b ³ _{11 September 2008 19 1999-2007 by Richard Alan Peters II 11 September 2008} b ⁴ _{20 1999-2007 by Richard Alan Peters II}

  Pengantar Pengolahan Citra Digital Pengantar Pengolahan Citra Digital Departemen Ilmu Komputer -IPB Departemen Ilmu Komputer -IPB

  Color Sensing / Color Perception Color Images

  These are approximations of

• Are constructed from three

  the responses to intensity maps. the visible spectrum of the “red”, “green”, and

• Each intensity map is projected

  “blue” receptors of a typical human eye. through a color filter (e.g., red, green, or blue, or cyan, magenta, or yellow) to create a single color image.

  The simultaneous red + blue • The intensity maps are overlaid response causes us to to create a color image. perceive a continuous range

• Each pixel in a color image is a

  of hues on a circle. No hue is greater than or less than any three element vector. _{11 September 2008 21} other hue. _{1999-2007 by Richard Alan Peters II 11 September 2008 1999-2007 by Richard Alan Peters II 22} Pengantar Pengolahan Citra Digital Pengantar Pengolahan Citra Digital Departemen Ilmu Komputer -IPB Departemen Ilmu Komputer -IPB NTSC Color Space = Y (Luminance) I (Hue) Q (Saturation)

  Color Color Images In Print Images

  CYMK Color Space on a CRT or

  LCD Display Images are separated into four Intensity images color bands, each of which is are projected printed as a grid regularly through dot-array spaced dots. A dot’s diameter color filters which are slightly offset varies in proportion to the from one another. _{11 September 2008 23 1999-2007 by Richard Alan Peters II 11 September 2008 24} intensity of the color. _{1999-2007 by Richard Alan Peters II}

  Pengantar Pengolahan Citra Digital Pengantar Pengolahan Citra Digital Departemen Ilmu Komputer -IPB Departemen Ilmu Komputer -IPB

  Standard Halftone Screen Angles Color

  The dot grids are created with a Cyan: 105 °

  Images screen that overlays the intensity

  Yellow: 90 ° images. in Print

  Magenta: 75 ° Black: 45 °

  CYMK Color Space The screens The four are oriented colors at different are angles. magenta,

  The resulting cyan, patterns are yellow, called and black _{11 September 2008 25 1999-2007 by Richard Alan Peters II 11 September 2008 26} “rosettes”. _{1999-2007 by Richard Alan Peters II}

  Pengantar Pengolahan Citra Digital Pengantar Pengolahan Citra Digital Departemen Ilmu Komputer -IPB Departemen Ilmu Komputer -IPB

  Color Separation / Halftoning Color Separation / Halftoning The original is separated into an intensity image for each of the four color _{11 September 2008} bands. _{27 1999-2007 by Richard Alan Peters II 11 September 2008 28 1999-2007 by Richard Alan Peters II}

  Pengantar Pengolahan Citra Digital Pengantar Pengolahan Citra Digital Departemen Ilmu Komputer -IPB Departemen Ilmu Komputer -IPB

  Color Separation / Halftoning Color Separation / Halftoning Each intensity image is

  Cyan Magenta multiplied by a corresponding “screen”,

  Yellow Black Each screened image is printed in its own color on the same page. _{11 September 2008 29 1999-2007 by Richard Alan Peters II 11 September 2008 30 1999-2007 by Richard Alan Peters II}

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  Brightness Perception Linear intensity changes are not seen as such. image intensity profile

  11 September 2008 ^{36 1999-2007 by Richard Alan} _{Peters II}

  Pengantar Pengolahan Citra Digital

  Color Perception: The Afterimage Effect Departemen Ilmu Komputer -IPB

  The color “negatives” saturate the local receptors so that when the color is removed the agonist (opposite) color receptors remain saturated.

  11 September 2008 ^{35 1999-2007 by Richard Alan} _{Peters II}

  11 September 2008 ^{34 1999-2007 by Richard Alan} _{Peters II}

  11 September 2008 ^{31 1999-2007 by Richard Alan} _{Peters II}

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  11 September 2008 ^{33 1999-2007 by Richard Alan} _{Peters II}

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  11 September 2008 ^{32 1999-2007 by Richard Alan} _{Peters II}

  Departemen Ilmu Komputer -IPB Pengantar Pengolahan Citra Digital

  Stare at the dot in the center of the image Color Perception: The Afterimage Effect

  255

  Pengantar Pengolahan Citra Digital Departemen Ilmu Komputer -IPB

  Brightness Perception The previous slide demonstrates the Weber-Fechner relation. The linear slope of the intensity change is perceived as logarithmic. g g _{1  2}

    g g  g _{1 2 g : Intensity 1 g 2 1 : Intensity 2}

  The green curve is the actual  g : Apparent change in brightness intensity; the blue curve is the _{11 September 2008} perceived intensity. _{37 1999-2007 by Richard Alan Peters II}