Pixel Size

1
Hi everyone,

I am trying to work out how big one pixel is on a display (my laptop, for starters, but ideally in a dynamic way). Screen ('PixelSize') should give this, right?

However, the documentation for Screen does not state what unit PixelSize returns in. When I run it on my laptop, I get

ans =

32


However, I have a 14' display that has a resolution of 1600x900, so a quick calculation says every pixel should be 0.0076 inches wide (or 0.0193 cm).

Can anyone help me out?
2
the documentation for Screen('OpenWindow') says that the pixelSize parameter refers to the bit depth of each pixel, not the pixel dimensions...


--- In psychtoolbox@yahoogroups.com, "jan.freyberg" <jan.freyberg@...> wrote:
>
> Hi everyone,
>
> I am trying to work out how big one pixel is on a display (my laptop, for starters, but ideally in a dynamic way). Screen ('PixelSize') should give this, right?
>
> However, the documentation for Screen does not state what unit PixelSize returns in. When I run it on my laptop, I get
>
> ans =
>
> 32
>
>
> However, I have a 14' display that has a resolution of 1600x900, so a quick calculation says every pixel should be 0.0076 inches wide (or 0.0193 cm).
>
> Can anyone help me out?
>
3
The way I do it in my lab is to find out the hostname and the set whatever display specific details I need from that:

% find out machine, configure properly
[tmp, machine] = dos('hostname');


switch lower(machine(1:end-1))
case 'take_dell'
stereoMode = 4;
scrnNum = 2;
lutFile = 'c:\alan\hpd256_9_23_11.mat';
case '3dtv'
% etc
end

On Thu, Dec 6, 2012 at 2:24 PM, elladawu <elladawu@...> wrote:


the documentation for Screen('OpenWindow') says that the pixelSize parameter refers to the bit depth of each pixel, not the pixel dimensions...

--- In psychtoolbox@yahoogroups.com, "jan.freyberg" <jan.freyberg@...> wrote:
>
> Hi everyone,
>
> I am trying to work out how big one pixel is on a display (my laptop, for starters, but ideally in a dynamic way). Screen ('PixelSize') should give this, right?
>
> However, the documentation for Screen does not state what unit PixelSize returns in. When I run it on my laptop, I get
>
> ans =
>
> 32
>
>
> However, I have a 14' display that has a resolution of 1600x900, so a quick calculation says every pixel should be 0.0076 inches wide (or 0.0193 cm).
>
> Can anyone help me out?
>


4
Hi Jan,

I usually do this to get my pixel size in degrees of visual angle:

screenDistCm = 60;
[window,dispRect] = Screen(whichScreen, 'OpenWindow');
[screemwidthMm]=Screen('DisplaySize',window);
screenwidthDeg = 2*atand(screemwidthMm/(20*screenDistCm));
degPerPixel = screenwidthDeg/dispRect(3);

of course pixel size in mm would be simpler:
mmPerPixel = screemwidthMm/dispRect(3);

But see the output of Screen DisplaySize? which tells you that this method may give you misleading results.

Best,
Max


Am 06.12.2012 um 23:28 schrieb Alan Robinson <arcogsci@...>:

 

The way I do it in my lab is to find out the hostname and the set whatever display specific details I need from that:


% find out machine, configure properly
[tmp, machine] = dos('hostname');


switch lower(machine(1:end-1))
    case 'take_dell'
        stereoMode = 4;
        scrnNum = 2;
        lutFile = 'c:\alan\hpd256_9_23_11.mat';
    case '3dtv'
% etc
end

On Thu, Dec 6, 2012 at 2:24 PM, elladawu <elladawu@...> wrote:
 


the documentation for Screen('OpenWindow') says that the pixelSize parameter refers to the bit depth of each pixel, not the pixel dimensions...

--- In psychtoolbox@yahoogroups.com, "jan.freyberg" <jan.freyberg@...> wrote:
>
> Hi everyone,
>
> I am trying to work out how big one pixel is on a display (my laptop, for starters, but ideally in a dynamic way). Screen ('PixelSize') should give this, right?
>
> However, the documentation for Screen does not state what unit PixelSize returns in. When I run it on my laptop, I get
>
> ans =
>
> 32
>
>
> However, I have a 14' display that has a resolution of 1600x900, so a quick calculation says every pixel should be 0.0076 inches wide (or 0.0193 cm).
>
> Can anyone help me out?
>




_____________________________________________________________

Dr. phil. Maximilian Bruchmann, Dipl. Psych.
Institut für Biomagnetismus und Biosignalanalyse
Universitätsklinikum Münster


Adresse:    Malmedyweg 15
                 48149 Münster
                 Telefon:    +49-(0)251-83-52547
E-Mail:      Maximilian.Bruchmann@...
Internet:    http://biomag.uni-muenster.de
_____________________________________________________________

5
Hi maximilian,

thanks for your help. This makes a lot of sense - digging around a little bit showed that PixelSize is something completely different!

Unfortunately my display does not return accurate numbers. I guess I will just have to calculate it by hand.

all the best,
Jan


On Fri, Dec 7, 2012 at 11:11 AM, Maximilian Bruchmann <Maximilian.Bruchmann@...> wrote:

Hi Jan,


I usually do this to get my pixel size in degrees of visual angle:

screenDistCm = 60;
[window,dispRect] = Screen(whichScreen, 'OpenWindow');
[screemwidthMm]=Screen('DisplaySize',window);
screenwidthDeg = 2*atand(screemwidthMm/(20*screenDistCm));
degPerPixel = screenwidthDeg/dispRect(3);

of course pixel size in mm would be simpler:
mmPerPixel = screemwidthMm/dispRect(3);

But see the output of Screen DisplaySize? which tells you that this method may give you misleading results.

Best,
Max


Am 06.12.2012 um 23:28 schrieb Alan Robinson <arcogsci@...>:

The way I do it in my lab is to find out the hostname and the set whatever display specific details I need from that:


% find out machine, configure properly
[tmp, machine] = dos('hostname');


switch lower(machine(1:end-1))
case 'take_dell'
stereoMode = 4;
scrnNum = 2;
lutFile = 'c:\alan\hpd256_9_23_11.mat';
case '3dtv'
% etc
end

On Thu, Dec 6, 2012 at 2:24 PM, elladawu <elladawu@...> wrote:


the documentation for Screen('OpenWindow') says that the pixelSize parameter refers to the bit depth of each pixel, not the pixel dimensions...

--- In psychtoolbox@yahoogroups.com, "jan.freyberg" <jan.freyberg@...> wrote:
>
> Hi everyone,
>
> I am trying to work out how big one pixel is on a display (my laptop, for starters, but ideally in a dynamic way). Screen ('PixelSize') should give this, right?
>
> However, the documentation for Screen does not state what unit PixelSize returns in. When I run it on my laptop, I get
>
> ans =
>
> 32
>
>
> However, I have a 14' display that has a resolution of 1600x900, so a quick calculation says every pixel should be 0.0076 inches wide (or 0.0193 cm).
>
> Can anyone help me out?
>




_____________________________________________________________

Dr. phil. Maximilian Bruchmann, Dipl. Psych.
Institut für Biomagnetismus und Biosignalanalyse
Universitätsklinikum Münster


Adresse: Malmedyweg 15
48149 Münster
Telefon: +49-(0)251-83-52547
E-Mail: Maximilian.Bruchmann@...
Internet: http://biomag.uni-muenster.de
_____________________________________________________________