# How can I draw a particular line pixel by pixel ?

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Teo Protoulis on 22 Mar 2018
Commented: Image Analyst on 23 Mar 2018
I have the below code in order to draw the line: y = m*x + b.
I want to draw the line pixel by pixel using the code below:
x1 = 6;
x0 = 3;
y1 = 7;
y0 = 2;
Dx = x1 - x0;
Dy = y1 - y0;
m = Dy / Dx;
b = y0 - (m*x0);
invm = 1 / m;
invmb = b* invm;
if (m<=1)
for x = x0:1:x1
y = (m*x) + b;
yp = floor(0.5 + y);
drawpixel(x,yp);
end
else
for y=y0:1:y1
x = invm*x - invmb;
xp = floor(0.5 + x);
drawpixel(xp,y);
end
end
How can I implement the drawpixel(xp, y) function ?
##### 2 CommentsShowHide 1 older comment
Teo Protoulis on 22 Mar 2018
I am studying for a university class and I have to go through different algorithms. Bresenham's is one I am going to have a look at. I should have also written drawpixel instead of plot.

Image Analyst on 22 Mar 2018
If you want to set/write a value, say 255, into some digital matrix (like an image) then you can do this:
function yourImage = drawpixel(yourImage, xp, y)
column = round(xp);
row = round(y);
yourImage(row, column, :) = 255; % Or whatever value you want.
Then to call that function in your loop, do this:
yourImage = drawpixel(yourImage, xp, y);
Note that images and line plots have the y axis direction flipped compared to one another, so if you want the plot on top of the image, you'll have to set ydir().
##### 2 CommentsShowHide 1 older comment
Image Analyst on 23 Mar 2018
No, you call imshow() instead of plot() because you have an image, not some x,y vectors. Since you created the matrix with the color values you want (i.e. the line is burned into the image with the right color), you simply call imshow() to display that matrix with the burned in line.