Using CreateProceduralSineGrating function to create colored gratings

thesnarkisaboojum · October 17, 2018, 9:51pm

Hello,

I am using the CreateProceduralSineGrating to create color modulated gratings. My goal is to create a grating which peaks at green cyan (RBG [0 0.8 0.5]) and troughs at middle cyan [0 0.5 0.5]. However, I have been unable to create what I want so far. The code I have used to create my gratings is below.

% To create the grating

backgroundColorOffsetCy = [0 0.5 0.5 1]; %RGBA offset color

[gratingidG, gratingrectG] = CreateProceduralSineGrating(windowPtr, screenXpixels, screenXpixels, backgroundColorOffsetCy, [], 1);

% To display the grating

modulateCol = [0 0.8 0.5];

propertiesMat = [0, 0.005, 1, 0];

Screen('DrawTexture', windowPtr, gratingidG, [], dstRect , Angle, [] , [], [modulateCol], [], [], propertiesMat' );

This code creates a grating similar to what can be seen in the attachment. It looks to peak at the right color however it fades into black instead of middle cyan. Any help in changing the creation commands to achieve what I want would be greatly appreciated.

Thanks,

Michael

debarshi_optometry · March 12, 2019, 5:54pm

Hi,

Thank you for sharing codes here. This codes are not running for me, There is a problem here:

Undefined function or variable 'windowPtr'.

Error in Gratings12 (line 3)

[gratingidG, gratingrectG] = CreateProceduralSineGrating(windowPtr, screenXpixels, screenXpixels,

backgroundColorOffsetCy, [], 1);

Would you please suggest me what to do nest?

Thank you,

Best,

Debarshi

thesnarkisaboojum · August 19, 2019, 5:59pm

Hello Debarshi,

I am very sorry about getting back to you so long after your initial question. So I was never able to specify the colors for a sine grating properly with that function. I ended up writing my own code to create an RGB matrix with exactly the color content I wanted to present.

That might be your best option depending on how exact you need to be your presentation.

Best,

Michael

m4liao · October 21, 2020, 10:09pm

HI Michael,

Can you explain how you created the RGB matrix? I’m trying to make colored gabors with equiluminant colors and this seemed relevant. Thanks!

Ming-Ray

Ian-Max-Andolina · October 22, 2020, 2:17am

Since this last post, PTB now has a CreateProceduralColorGrating.m function added, you can see it working in ProceduralColorGratingDemo.m…

github.com

kleinerm/Psychtoolbox-3/blob/master/Psychtoolbox/PsychDemos/ProceduralColorGratingDemo.m

function ProceduralColorGratingDemo(color1,color2,baseColor)
% ProceduralColorGratingDemo() -- demo color grating procedural shader
% stimuli
%
%
% This demo shows how to use procedural color gratings. Color gratings 
% have two color sources, rather than one. They are a useful stimulus
% class for e.g. understanding opponenet color channels. The standard PTB
% grating shader cannot generate this class of grating. The procedural
% shader can generate sinusoidal or square wave gratings, and you can set a
% radial aperture.
%
%
% Optional Inputs are:
% color1 -- the first color of the grating, default is red [1 0 0 1]
% color2 -- the second color of the grating, default is green [0 1 0 1]
% baseColor -- the base color from which color1 and color2 are blended
% depending on contrast. Normally this would be set to your background
% color in PTB; default in this demo is the background color [0.5 0.5 0.5 1].
%

This file has been truncated. show original

This uses the GLSL mix function to blend between two colours against a background colour. If you want to generate a gabor you could use this with an overlaid gaussian mask, or modify the GLSL code itself to spatially modulate the grating with a gaussian (look at the procedural gabor code for guidance).

Now, how to choose equiluminant colors is another issue, depending on whether you require physical or perceptual equilumance

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Using CreateProceduralSineGrating function to create colored gratings

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