1. Computer Programming Methodology Luminance
COS 130
Computer Programming Methodology
Luminance

2. More about color or lack there of Luminance

3. Luminance Used to represent color as shades of grey
The eye sees different colors with more or less intensity
Therefore we weight different colors when converting them to grey

4. Luminance We will use this formula
to go from RGB to luminance (gray scale)
red * green * blue * 0.11

5. Luminance Formula in Java
int red;
int green;
int blue;
int gs;
. . .
gs = red * green * blue * 0.11;
What happens here?
Promoted to double
int
double
Truncate!

6. A cast (in this case to an int)
Casting Primitives
Tells the compiler – Just Trust Me, I know what I’m doing
A cast (in this case to an int)
gs = (int) (red * green * blue * 0.11);

7. When to use Promotion Casting Put a small thing into a big thing
Generally safe
Happens automatically
Casting
Put a big thing into a small thing
You must code
May result in errors
Example int n = (int) 2.34

8. Rounding
When we truncate we would really like to round to the closest integer
int num = (int)3.999;
In this example we would like num to end up as 4 not 3
So we add .5
int num = (int) ( );

9. Final Version Luminance in Java
gs = (int) (red * green * blue * );

10. What values are allowed?
gs = (int) (red * green * blue * );
System.out.write(gs);
0 through 255
public static int clamp(int n) {
if(n < 0) return 0;
if(n > 255) return 255;
return n; }
gs = (int) (red * green * blue * );
gs = clamp(gs);
System.out.write(gs);