finding equiluminance for a pair of colors

1
Does anyone have matlab software using the psych toolobox or
standalone that allows measuring equiluminance points for arbitrary
colors? IE something like this java demo:

http://www.cs.ubc.ca/nest/imager/contributions/flinn/Illusions/CB/cb.html

Thanks!
2
Hi Sharon,
I have to prepare an experiment in which the isoluminant point is
found in a similar way.
I have to create chromatic-contrast patterns (red-green or blue-
yellow) superimposing (out of phase by 180 degrees) red-black and
green-black (or blue-black and yellow-black) gratings.
I would like to determine the equiluminance point for every subject
with a variant of the method of heterochromatic flicker photometry.
While the red-green gratings were sinusoidally reversed at 15 Hz,
subjects adjust ratio of red to total luminance to minimized the
perception of flicker.
My question is: how can I control the luminance of gratings in the
monitor? What's the way to change luminance as in the Flinn demo?
Have I only to vary the Y coordinate of xyY CIE 1931, taking x and y
constant at a fixed chromaticity for red and for green?
Thanks a lot in advance!!!

Roberta Fagioli
University of Pavia


--- In psychtoolbox@yahoogroups.com, "sharon.sally" <ssally@...>
wrote:
>
> Hi Alan,
>
> Sure, I've done that.
>
> The Flinn demo is to find equiluminance for moving images only.
If you have static
> images you'll use heterochromatic flicker photometry.
>
> Either way making the stimulus is very easy –first create your
patterns. In the Flinn demo
> (from Anstis' work) there are just 4 block images shown in
sequence. Eg.
>
> function g= fillpattern
> a=zeros(140,20);
> mp=ones(10);
> mp2=mp.*-1;
> nn=0;
> for n=1:14
> mpp=mp
> if mod(n, 2)
> mpp=mp2;
> end
> a(1:10,1+nn:10*n)=mpp;
> nn=nn+10;
> end
> g=a;
>
> If you're doing flicker photometry you'll create two images of
squarewave gratings 180
> degrees out of phase.
>
> For colored images mpp could be something like mp*.25 and mp*.57
>
>
> See driftdemo
> SCREEN(w(1),'PutImage',gray+inc*m);
>
> 127.5+127.5*.57=200.1
>
> for OS9 below
>
> clutss=SCREEN(window,'GetClut');
> clutss(200,1:3)=[255 0 0] % one (eg. red) stays constant
> clutss(160,1:3)=[0 trialtheta 0];
> SCREEN(window, 'SetClut', clutss);
>
> For OSX use ReadNormalizedGammaTable and LoadNormalizedGammaTable
>
> That's it!
>
> Sharon Sally
>
> --- In psychtoolbox@yahoogroups.com, "Alan Robinson"
<x_e_o_s_yahoo@> wrote:
> >
> > Does anyone have matlab software using the psych toolobox or
> > standalone that allows measuring equiluminance points for
arbitrary
> > colors? IE something like this java demo:
> >
> >
http://www.cs.ubc.ca/nest/imager/contributions/flinn/Illusions/CB/cb.
html
> >
> > Thanks!
> >
>
3
Hi Roberta,
Mario send me this email conerning a problem that I can not solve and I
asked me to send you this response too:

Ok, i have a hunch but i'm getting sick, so debugging must wait.

Try to add this to the top of your script as work-around, and
tell roberta fagioli to try the same with her problem.

Screen('Preference', 'VBLTimestampingMode', -1);

i'm offline, best,
-mario

Hope it can help you!!!
Best, Seb
4
Dear Sharon,
thank you very much for the suggestion!!!
Now, I will try to create my stimulus with these coordinates.
Greetings from Italy!

Roberta

--- In psychtoolbox@yahoogroups.com, "sharon.sally" <ssally@...>
wrote:
>
> Hi Roberta,
>
> You can work in hue, value, saturation coordinates and translate
back and forth to RGB.
> See Matlab's HSV2RGB / RGB2HSV mfiles. This way you can keep hue
and saturation
> constant and change value. Take a look at Matlab's colormap(hsv)
to get started.
>
> colormap('hsv');
> ww=colormap
> www=rgb2hsv(ww)
>
> All values are from 0 to 1.
>
> Best,
>
> Sharon
>
> --- In psychtoolbox@yahoogroups.com, "roberta.fagioli"
<roberta.fagioli@> wrote:
> >
> > Hi Sharon,
> > I have to prepare an experiment in which the isoluminant point
is
> > found in a similar way.
> > I have to create chromatic-contrast patterns (red-green or blue-
> > yellow) superimposing (out of phase by 180 degrees) red-black
and
> > green-black (or blue-black and yellow-black) gratings.
> > I would like to determine the equiluminance point for every
subject
> > with a variant of the method of heterochromatic flicker
photometry.
> > While the red-green gratings were sinusoidally reversed at 15
Hz,
> > subjects adjust ratio of red to total luminance to minimized the
> > perception of flicker.
> > My question is: how can I control the luminance of gratings in
the
> > monitor? What's the way to change luminance as in the Flinn
demo?
> > Have I only to vary the Y coordinate of xyY CIE 1931, taking x
and y
> > constant at a fixed chromaticity for red and for green?
> > Thanks a lot in advance!!!
> >
> > Roberta Fagioli
> > University of Pavia
> >
> >
> > --- In psychtoolbox@yahoogroups.com, "sharon.sally" <ssally@>
> > wrote:
> > >
> > > Hi Alan,
> > >
> > > Sure, I've done that.
> > >
> > > The Flinn demo is to find equiluminance for moving images
only.
> > If you have static
> > > images you'll use heterochromatic flicker photometry.
> > >
> > > Either way making the stimulus is very easy –first create your
> > patterns. In the Flinn demo
> > > (from Anstis' work) there are just 4 block images shown in
> > sequence. Eg.
> > >
> > > function g= fillpattern
> > > a=zeros(140,20);
> > > mp=ones(10);
> > > mp2=mp.*-1;
> > > nn=0;
> > > for n=1:14
> > > mpp=mp
> > > if mod(n, 2)
> > > mpp=mp2;
> > > end
> > > a(1:10,1+nn:10*n)=mpp;
> > > nn=nn+10;
> > > end
> > > g=a;
> > >
> > > If you're doing flicker photometry you'll create two images of
> > squarewave gratings 180
> > > degrees out of phase.
> > >
> > > For colored images mpp could be something like mp*.25 and
mp*.57
> > >
> > >
> > > See driftdemo
> > > SCREEN(w(1),'PutImage',gray+inc*m);
> > >
> > > 127.5+127.5*.57=200.1
> > >
> > > for OS9 below
> > >
> > > clutss=SCREEN(window,'GetClut');
> > > clutss(200,1:3)=[255 0 0] % one (eg. red) stays constant
> > > clutss(160,1:3)=[0 trialtheta 0];
> > > SCREEN(window, 'SetClut', clutss);
> > >
> > > For OSX use ReadNormalizedGammaTable and
LoadNormalizedGammaTable
> > >
> > > That's it!
> > >
> > > Sharon Sally
> > >
> > > --- In psychtoolbox@yahoogroups.com, "Alan Robinson"
> > <x_e_o_s_yahoo@> wrote:
> > > >
> > > > Does anyone have matlab software using the psych toolobox or
> > > > standalone that allows measuring equiluminance points for
> > arbitrary
> > > > colors? IE something like this java demo:
> > > >
> > > >
> >
http://www.cs.ubc.ca/nest/imager/contributions/flinn/Illusions/CB/cb.
> > html
> > > >
> > > > Thanks!
> > > >
> > >
> >
>