Table of Contents of Series Articles
Chapter 2 Main Color Extraction and Color Space Transformation
Table of contents
Table of Contents of Series Articles
Preface
Conversion between HSV color space and RGB color space .
1. HSV and RGB color spaces
RGB colors are the most commonly used, namely red (R), green (G) and blue (B).
H(hue) in HSV color means hue, which is identified by color name, such as red, orange, green. It is measured in angle, from -180° to 180°, or from 0° to 360°; S(saturation) means Chroma or saturation refers to the depth of a color. For example, red can also be divided into dark red and light red due to different concentrations. S is measured in percentage, from 0% to 100% of full saturation; V (value) represents Brightness refers to the lightness or darkness of a color, usually measured as a percentage, from 0% black to 100% white.
2. Color conversion
1. RGB to HSV
RGB to HSV is relatively simple to implement.
Before calculating the formula, there are three assumptions:
- Let the value of (r, g, b) be a real number between 0 and 1
- Let max be equal to the largest of r, g, b
- Let min equal to the smallest of r, g, b
The formula is as shown below:
code show as below:
def RGB2HSV(r,g,b):
r, g, b = r / 255, g / 255, b / 255
ma = max(r, g, b)
mi = min(r, g, b)
diff = ma - mi
if ma == mi:
h = 0
elif ma == r and g >= b:
h = 60 * ((g - b)/diff) + 0
elif ma == r and g < b:
h = 60 * ((g - b)/diff) + 360
elif ma == g:
h = 60 * ((b - r)/diff) + 120
elif ma == b:
h = 60 * ((r - g)/diff) + 240
if ma == 0:
s = 0
else:
s = diff / ma
v = ma
return h, s, v
2. HSV to RGB
Converting HSV to RGB is more difficult than the above.
Two points to note:
1 Parameter input range h(0~360), s(0% ~ 100%), v(0% ~ 100%) 2 Conversion results R(0~255), G(0~255), B(0~255 ), if you need to convert to 0~100, just change the following multiplication by 255 to multiplication by 100
The formula is as follows:
The implementation code is as follows:
def HSV2RGB(h, s, v):
# s, v = s / 100, v /100
i = round(h / 60) % 6
f = (h / 60) - i
p = v * (1 - s)
q = v * (1 - f * s)
t = v * (1 - (1 - f) * s)
R, G, B = 0, 0, 0
if i == 0:
R, G, B = v, t, p
elif i == 1:
R, G, B = q, v, p
elif i == 2:
R, G, B = p, v, t
elif i == 3:
R, G, B = p, q, v
elif i == 4:
R, G, B = t, p, v
elif i == 5:
R, G, B = v, p, q
r, g, b = round(R * 255), round(G * 255), round(B * 255)
return r, g, b
3. Complete code
The complete code can be downloaded on GitHub. If you are interested, you might as well give me a star, haha.
https://github.com/Liangliangb/Image-main-color-extraction.git