Android Camera Live Filter (vi)

HSL Color Mode 1. Color HSL

H:hue Hue
Saturation of S:saturation
L:lum brightness

2. Overview

• The HSL color model is a color standard for industry, which is the color of hue, saturation, and brightness of three channels by varying the color channels of tones (H), saturation (S), luminance (L), and their superposition to each other (three). This standard almost includes all the colors that human vision can perceive, and is one of the most widely used color systems.
• HSL color mode uses the HSL model to assign the HSL component of each pixel in an image to a strength value in the 0~255 range. The HSL image uses only three channels, allowing them to blend in different proportions and reproduce 16777216 colors on the screen.
• In HSL mode, values from 0 to 255 can be used for each HSL component. (where L is a gradient from black (0) to White (255)).
  

3. HSL and RGB conversion

A) algorithm description for RGB→HSL

Step 1: Turn the RGB values into "0,1" values.
Step 2: Find the maximum value in R,g and B.
Step 3: Set l= (Maxcolor + mincolor)/2
Step 4: If the maximum and minimum color values are the same, which means gray, then S is defined as 0, and H is undefined and is usually written in the program as 0.
Step 5: Otherwise, test L:
If l<0.5, s= (maxcolor-mincolor)/(Maxcolor + mincolor)
If l>=0.5, s= (maxcolor-mincolor)/(2.0-maxcolor-mincolor)
Step 6: If r=maxcolor, h= (g-b)/(Maxcolor-mincolor)
If G=maxcolor, h=2.0+ (b-r)/(Maxcolor-mincolor)
If B=maxcolor, h=4.0+ (r-g)/(Maxcolor-mincolor)
Step 7: From the calculation of the 6th step, H is divided into the 0~6 area. The RGB color space is a cube and the HSL color space is two hexagon cones, where l is the main diagonal of the RGB cube. Therefore, the vertices of the RGB cube: Red, yellow, green, cyan, blue, and magenta become the vertices of the HSL hexagonal, and the numerical 0~6 tells us which part H is. h=h*60.0, if H is negative, add 360.

b) algorithm description for Hsl→rgb

Step 1: If s=0, indicates gray, define R,G and B are all L.
Step 2: Otherwise, test L:
If l<0.5,temp2=l* (1.0+s)
If l>=0.5,temp2=l+s-l*s
Step 3: TEMP1=2.0*-TEMP2
Step 4: Convert H to 0~1.
Step 5: For R,g,b, calculate an additional temporary value of Temp3. Here's how:
For R, temp3=h+1.0/3.0
For G, Temp3=h
For B, temp3=h-1.0/3.0
If temp3<0, temp3=temp3+1.0
If temp3>1, temp3=temp3-1.0
Step 6: Do the following tests for R,g,b:
If 6.0*temp3<1,color=temp1+ (TEMP2-TEMP1) *6.0*temp3
Else if 2.0*TEMP3<1,COLOR=TEMP2
Else if 3.0*temp3<2,
color=temp1+ (TEMP2-TEMP1) * ((2.0/3.0)-temp3) *6.0
Else COLOR=TEMP1

Example

Android Camera Live Filter (vi)