blue filter

asnne

Hi,

I'm trying to show grayscale pictures in blue in an inline_script.
I want to do this by drawing a transparent blue picture on top of it (because I have about 4200 pictures to colorize myself otherwise).

The pseudo-code would than be something like this:

exp.canvas = self.offline_canvas()
exp.canvas.image(picture, x, y, etc)
exp.canvas.rect(x, y, w, h, color=blue, fill=True, alpha=0.5)

I've already tried it with GratingStim from psychopy.visual, but that opened a new screen next to the screen that the picture was shown on)

Does anyone know a solution that'll help?

sebastiaan

Hi,

A semitransparent overlay changes the colors, but differently from a color-swap—which is presumably what you're after, right? For example, a blue overlay would make a black background blueish.

Below is a simple script that reads an image file, and then mutes one or more of the color channels. So it does proper recoloring.

import os
from scipy import misc


def color_filter(source, target, red=False, green=False, blue=False):

    a = misc.imread(pool[source])
    if not red:
        a[:,:,0] = 0
    if not green:
        a[:,:,1] = 0
    if not blue:
        a[:,:,2] = 0        
    misc.imsave(os.path.join(exp.pool_folder, target), a)

Do you see the logic? A bitmap is just an array, and the third dimension has the color channels [red, green, blue]. And you can mute a color channel (i.e. remove a color) by setting it to 0.

Now say that you have an image file in the file pool called original.png. Then the following would create a filtered image file in the file pool called blue.png:

color_filter('original.png', 'blue.png', blue=True)

You can just do this on every trial, and the use the filtered image in a sketchpad, canvas, or what have you.

Cheers!
Sebastiaan