[예습] Basics of Color

Basics of Color

Primary colors of light(빛의 삼원색)

• Blue
• Green
• Red

(OpenCV순)

Secondary colors of light(색의 삼원색)

• Magenta (red + blue)
• Yellow (red + green)
• Cyan (green + blue)

Achromatic color(무채색)

• Without color 색상 정보 존재x
• The ratio of each color component is same

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Color Models

RGB

• R-channel
• G-channel
• B-channel
• 각각의 채널에 대한 intensity level = 256 [0 ~ 255]
  • Red = (255, 0, 0)
  • White = (255, 255, 255) -> 무채색
  • Black = (0, 0, 0) -> 무채색

Achromatic color: Black과 White의 대각선

HSI

• Hue-channel
  • the dominant wavelength in a mixture of light waves (색상)
• Saturation-channel
  • the relative purity or the amount of white light mixed (채도)
  • 색을 표현할 때 ‘연하다’, ‘진하다’, ‘탁하다’ 등과 같은 정도를 나타냄
  • 흰색과 순수색의 혼합 비율(0 ~ 100%)
  • S가 클수록 -> clear color
  • Saturation = 0 = achromatic color
• Intensity-channel(Brightness)
  • achromatic notion of intensity (명도)
  • I가 클수록 -> bright color
  • HSI ≅ HSV (Value) Similar or Same

Achromatic color: 도형의 심

Channel	Model	Range	OpenCV
Hue	원의 각도	0<H<360	0<H<180
Saturation	원의 반지름	0<S<1	0<S<255
Intensity	도형의 높이	0<V<1	0<V<255

YCbCr (or YUV)

• Y: Brightness (intensity level)
• Cb: Difference between blue value and brightness (B-Y)
• Cr: Difference between red value and brightness(R-Y)

Ex) B → Y ≒ B
→ B - Y > 0 (Normally) Y(Brightness) → (R+G+B)/3)

Grayscale image(흑백 사진)

• Hue, Saturation = 0
• The lightness(or brightness) is the only parameter
• 0(Black)-128(Gray)-255(White)