RGB to HSV, HSV to RGB Conversion Calculator,Program to Change RGB color model to HSV color model

 

RGB to HSV, HSV to RGB Conversion Calculator

The HSV color model describes colors according to their Hue, Saturation, and Value. In some computer graphics programs, it is used as an alternative to the RGB system to quantify colors.

In HSV, hue is a number in the interval [0, 360). A color's hue is its general position on a color wheel, where red is at 0°, green is at 120°, and blue is at 240°. For example the RGB code of a yellow/orange color has high red and green components and a low blue component, with the red level slightly higher than the green. On the color wheel, the angle of this hue is a little less than 60°. The hue of any neutral color--white, gray, or black--is set at 0°.

Value, in HSV, is the highest value among the three R, G, and B numbers. This number is divided by 255 to scale it between 0 and 1. In terms of perception, HSV Value represents how light, bright, or intense a color is. Value does not distinguish white and pure colors, all of which have V = 1.

Converting RGB to HSV

Given three numbers R, G, and B (each between 0 and 255), you can first define m and M with the relations

M = max{R, G, B}
m = min{R, G, B}.

And then V and S are defined by the equations

V = M/255
S = 1 - m/M     if M > 0
S = 0              if M = 0.

As in the HSI and HSL color schemes, the hue H is defined by the equations

H = cos^-1[ (R - ½G - ½B)/√R² + G² + B² - RG - RB - GB ]            if G ≥ B, or
H = 360 - cos^-1[ (R - ½G - ½B)/√R² + G² + B² - RG - RB - GB ]    if B > G.

Inverse cosine is calculated in degrees.

Converting HSV to RGB

Given the values of H, S, and V, you can first compute m and M with the equations

M = 255V
m = M(1-S).

Now compute another number, z, defined by the equation

z = (M-m)[1 - |(H/60)mod_2 - 1|],

where mod_2 means division modulo 2. For example, if H = 135, then (H/60)mod_2 = (2.25)mod_2 = 0.25. In modulo 2 division, the output is the remainder of the quantity when you divide it by 2.

Now you can compute R, G, and B according to the angle measure of H. There are six cases. When 0 ≤ H < 60,

R = M
G = z + m
B = m.

If 60 ≤ H < 120,

R = z + m
G = M
B = m.

If 120 ≤ H < 180,

R = m
G = M
B = z + m.

When 180 ≤ H < 240,

R = m
G = z + m
B = M.

When 240 ≤ H < 300,

R = z + m
G = m
B = M.

And if 300 ≤ H < 360,

R = M
G = m
B = z + m.

Given RGB color range, our task is to convert RGB color to HSV color.
RGB Color Model : 
The RGB color model is an additive color model in which red, green and blue light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three additive primary colors, red, green, and blue. 
 
HSV Color Model : 
HSV – (hue, saturation, value), also known as HSB (hue, saturation, brightness), is often used by artists because it is often more natural to think about a color in terms of hue and saturation than in terms of additive or subtractive color components. HSV is a transformation of an RGB colorspace, and its components and colorimetry are relative to the RGB colorspace from which it was derived. 
 Examples : 

Input : r, g, b = 45, 215, 0
Output :
h, s, v = 107.44186046511628, 100.0, 84.31372549019608


Input : r, g, v = 31, 52, 29
Output :
h, s, v = 114.78260869565217, 44.230769230769226, 20.392156862745097

Below is the implementation of above approach : 

# Python3 program change RGB Color
# Model to HSV Color Model
  
def rgb_to_hsv(r, g, b):
  
    # R, G, B values are divided by 255
    # to change the range from 0..255 to 0..1:
    r, g, b = r / 255.0, g / 255.0, b / 255.0
  
    # h, s, v = hue, saturation, value
    cmax = max(r, g, b)    # maximum of r, g, b
    cmin = min(r, g, b)    # minimum of r, g, b
    diff = cmax-cmin       # diff of cmax and cmin.
  
    # if cmax and cmax are equal then h = 0
    if cmax == cmin: 
        h = 0
      
    # if cmax equal r then compute h
    elif cmax == r: 
        h = (60 * ((g - b) / diff) + 360) % 360
  
    # if cmax equal g then compute h
    elif cmax == g:
        h = (60 * ((b - r) / diff) + 120) % 360
  
    # if cmax equal b then compute h
    elif cmax == b:
        h = (60 * ((r - g) / diff) + 240) % 360
  
    # if cmax equal zero
    if cmax == 0:
        s = 0
    else:
        s = (diff / cmax) * 100
  
    # compute v
    v = cmax * 100
    return h, s, v
  
  
''' Driver Code '''
# print(rgb_to_hsv(45, 215, 0))
# print(rgb_to_hsv(31, 52, 29))
  
print(rgb_to_hsv(129, 88, 47))
Output
(30, 63.5659, 50.5882)
Time Complexity: O(1)
Auxiliary Space: O(1), As constant extra space is used.