How to measure text letter size in pixels?

I am trying to put up a letter (x) and measure it's height and width in pixels. I would like to do it for a number of different size fonts. I thought there was a scan command that would start at the top of the screen and scan until it ran into the text, then record that value. I also would like to be able to put up two letter X's and measure the distance in pixels between them.

[Eamon]

Do you need to do this in Matlab? You can use the measurement tools in Fiji or ImageJ to do this.

[T Shep]

Yeah, I have to be able to do this in real time.

[Image Analyst]

You didn't respond to my "Answer" below. Did you see it? Will that work for you?

Answer 1

[Image Analyst]

If you have the Computer Vision System Toolbox, try insertText(): http://www.mathworks.com/help/vision/ref/inserttext.html

[T Shep]

Sorry, the answer was collapsed and I did not see it. This is what I have so far. I can scan the height and width of the first letter but I want to be able to continue on to the second letter and scan it as well.

function xw = x_width_space(img)
fW0=0;
NW1=0;
NW2=0;
for i=1:size(img,1);
    if ~isempty(find(img(:,i) < 50))  %%if pixel val is < 50, inked row.
        if fW0==0
            NW1=i;  %%starting point
            fW0=1;
        end
    else % if non-ink row
        if fW0==1
            NW2=i;  %%ending point + 1 row
            fW0=0;

          end

      end
  end

Answer 2

[Walter Roberson]

Create a uicontrol('style','text') and appropriate FontName, FontSize, FontUnits, FontWeight, FontAngle. Do not worry about the Position. You can set the Visibility to off. Once it has been set up, set the uicontrol Units to pixels .

Now for each character to be tested, set the String property of the uicontrol to just that one character, and then ask for the Extent property of the control. This will tell you how big the control would have to be to hold the string. Record it, keep going with the next desired character, or set the FontSize and ask again, and so on.

After you are done, delete the uicontrol.

[T Shep]

Sorry, this is the fill code. I can measure the width and height of the first letter, but I am unable to move on to the second letter. I want to be able to find the spacing in between the first and the second letter in this loop. The function I use is at the bottom of this script.

ptstart = 7; %%%%%%%starting pt
ptend = 250; %%%%%%%ending pt
fonttype = 'Courier'; %%%%%%%ending pt

for i = ptstart:ptend % pt sizes
    Screen('TextSize',window,i);
    DrawFormattedText(window, repmat('x',1,2), 'center', 'center',0); % write formatted statement to offsreen buffer
    Screen('flip',window);
    img = Screen('GetImage',window);
    xh(i-6) = x_height(img(:,:,1)) % x-height in pixels
    xw(i-6) = x_height(img(:,:,1)') % x-width in pixels
end
x = [ptstart:ptend]; % pt size
ptpxw = [ x; xh; xw]; % row 1: pt size;  row 2: pixel #

Screen('Closeall');
ShowCursor;
time = datestr(now);
%%save lookup tables
%save('fontsize_calibrated2.mat', '-mat','time','ptpxw'); %%,'file_content');
save('fontsize_calibrated3.mat', '-mat',  'time','ptpxw'); %%,'file_content');

function xw = x_height(img)
f0=0;
N1=0;
N2=0;
for i=1:size(img,1);
    if ~isempty(find(img(i,:) < 50))  %%if pixel val is < 50, inked row.
        if f0==0
            N1=i;  %%starting point
            f0=1;
        end
    else % if non-ink row
        if f0==1
            N2=i;  %%ending point + 1 row
            f0=0;
        end
    end
end
xw = N2-N1;
%

[Walter Roberson]

If you want to know about how Psychtoolbox positions characters, you need to talk to the Psychtoolbox people http://psychtoolbox.org/