## Class 37 — April 17

## Image visualization

I draw from the past – Wonder about the present – Think of the future

### Look both ways

### HW Downloads

### Sepia

- There is no one formula for defining a Sepia pixel conversation. The one used here comes from Microsoft.

- For pixel
`(r,g,b)`

, the Sepia conversion is`(sr,sg,sb)`

where

sr, sg, sb = int( min( i, 255 )), int( min( j, 255 )), int( min( k, 255 )),

where

`i, j, k`

are

i = .393r + .769g + .189b

j = .349r + .686g + .168b

k = .272r + .534g + .131b

| |

### Palette reduction

- Sometimes to save computer memory, software developers perform a palette reduction of colors used in image representation.

- Our reduction scheme will use an eight-color palette

- Black, White, Red, Green, Blue, Yellow, Magenta, and Cyan; that is,
`(0,0,0), (255,255,255), (255,0,0), (0,255,0), (0,0,255), (255,255,0), (255,0,255),`

and`(0,255,255)`

- In a palette reduction, a pixel
`(r,g,b)`

is replaced by the pixel in in the palette it is*closest*to. The*distance*between pixels`(r1,g1,b1)`

and`(r2,g2,b2)`

equals

abs(r1 - r2) + abs(g1 - g2) + abs(b1 - b2)

- Note there is built-in function
`abs()`

for calculating absolute values.

| |