Color Standards A pixel color is represented as a point in 3-D space. Axis may be labeled as independent colors such as R, G, B or may use other independent indicators such as Hue, lightness, saturation. RBG, HSV, HSL are the most popular. 240-373 Image Processing

RGB RGB (Red green blue) For CRT display (TV, computer monitor) Additive combination of r g and b 240-373 Image Processing

HSV HSV (Hue Saturation Value) Hue is effectively a measure of the wavelength of the main color. It has a value between 0-255 (0-360o, Red = 0o, Green=120o and Blue=240o.) Hue can be calculated from RGB values as follows: Rh = R - min (R, G, B) Gh = G - min (R, G, B) Bh = B - min (R, G, B) At least on of these values is 0. Hue value is in between. 240-373 Image Processing

HSV For example if Rh = 0 Hue angle = (240xBh + 120xGh ) / (Bh + Gh) If two are zero, then hue is the angle corresponding to the third non-zero color. If three are zero, then there is no color hue. The monitor will display a gray level (between black and white). 240-373 Image Processing

Saturation Saturation is the amount of pure hue in the final color If Saturation = 0, final color is without hue ( white light only) If Saturation = 255, no white light in final color Saturation = (max(R,G,B) - min (R,G,B)) / max(R,G,B) 240-373 Image Processing

Value Value (brightness) is a measure of the intensity of the brightest component and given by Value = max(R,G,B) 240-373 Image Processing

The HSV Model 240-373 Image Processing

HSV Example Given R=100, G=200, B= 40, convert this RGB color model to HSV. Rh = 100 - min(100,200,40) = 60 Gh = 200 - min (100,200,40) = 160 Bh = 40 - min (100,200,40) = 0 H = (60*0 + 160*(120*256/360))/(60+160) 240-373 Image Processing

HSV Example (Continued) Saturation = (max(R,G,B) - min (R,G,B)) / max(R,G,B) = (max(100,200,40)-min(100,200,40))/ max(100,200,40) = (200-40)/200 = 0.8 = 80% Saturation = 80*256/100 = 204 Value = max(100,200,40) = 200 = 200*100/256 = 78% 240-373 Image Processing

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HLS HLS (Hue Lightness Saturation) Similar to HSV except that the hue angle start at Blue = 0o, and the model is double cone with a lightness axis going from L=0 (black) to L=1 (white) For HLS, hue is calculated the same way as for HSV model except Blue = 0 and lightness and saturation are given by: Lightness = (max(R,G,B) - min(R,G,B))/2 (max+min)/(max-min) if L <= 0.5 Saturation = (max-min)/(2-max-min) otherwise 240-373 Image Processing

HLS 240-373 Image Processing

CMY & CMYK CMY (Cyan Magenta Yellow) เป็นระบบสีที่พัฒนาขึ้นมาใช้สำหรับการพิมพ์ภาพสีโดยมีสีหลักคือสี Cyan Magenta และ Yellow ซึ่งเรียกว่า Subtractive primaries Color (สีแดง เขียวและน้ำเงิน เรียกว่า Additive primaries Color) ระบบสีแบบ CMY สามารถหาได้โดยการนำเอาสีในระบบ RGB ลบกับสีขาวดังนี้คือ 240-373 Image Processing

CMY & CMYK ระบบสี CMY จะนำไปใช้สำหรับการพิมพ์ภาพสีแต่ยังไม่ดีเท่าที่ควรเนื่องจากไม่ยังไม่สามารถสร้างสีดำได้อย่างถูกต้อง ดังนั้นจึงมีการใช้ระบบ CMYK แทนโดย K แทนสีดำ 240-373 Image Processing

The Human Vision Better than any camera yet developed Eye has 2 classes of discrete light receptors; Cones and rods 6-7 million cones, sensitive to bright light >= 75 Million rods, sensitive to light intensity but not color eye color perceptions 240-373 Image Processing

Color Additive Problem with CRT 240-373 Image Processing