# [Numpy-discussion] color filtering

Stéfan van der Walt stefan@sun.ac...
Wed Sep 17 11:37:53 CDT 2008

```Hey Paul

Maybe this helps:

# silly algorithm for guessing blue pixels
>>> bluemask = (a[...,2] > 1.25*a[...,1]) & (a[...,2] > 1.25*a[...,0])

array([[107,  11, 185],
[101,  91, 251],
[ 61,  23,  79],
[ 25, 131, 211],
[169,  83, 214],
[  2,  88, 216],
[ 71,  78, 250],
[ 23, 127, 183]], dtype=uint8)

Cheers
Stéfan

2008/9/17 paul taney <paultaney@yahoo.com>:
> I need to do a color filter;  I have it working in python
> but it runs forever on some of my images.  And I dont know
> enuf c or c++ to use weave (or Boost or Pyrex or...)

> # But while testing we can use:
>
> import numpy as np
>    a = np.array(
>    [[[ 64, 237, 108],  #  x  y
>      [185, 240,  68],  # [0, 1]
>      [ 17, 116,  55],  # [0, 2]
>      [107,  11, 185],  # [0, 3] is blue
>      [154,  30,  52]], # [0, 4]
>
>     [[251,  73, 150],  #  x  y
>      [ 47, 225,  97],  # [1, 1]
>      [101,  91, 251],  # [1, 2] is blue
>      [ 61,  23,  79],  # [1, 3]
>      [161,  22, 165]], # [1, 4]
>
>     [[  4, 162, 188],  # [2, 0]
>      [ 25, 131, 211],  # [2, 1]
>      [162, 112, 177],  # [2, 2]
>      [169,  83, 214],  # [2, 3] is blue
>      [254, 139,  95]],
>
>     [[  2,  88, 216],  # [3, 0] is blue
>      [230,  63, 192],
>      [ 71,  78, 250],  # [3, 2] is blue
>      [113, 151, 142],
>      [104,  65, 127]],
>
>     [[  6, 191, 220],  # [4, 0] is blue
>      [ 38, 141,   4],
>      [245,  41,  23],
>      [ 23, 127, 183],  # [4,] is blue
>      [165,  24,   5]]], np.uint8)
```