Export/Rasterize alpha shape to bitmap

Question

I build an alpha shape from some points (example given in code) and want to export the shape to a raster graphics format. I need the shape only, not the plot markings (axis, scales ect).

I need only the resulting triangle on white ground as a bitmap. Scale needs to be 1 unit = 1 pixel.

x = [0 10 20 30 30 30 15];
y = [0 0 0 0 15 30 15];

shape = alphaShape (x',y');

plot (shape, 'FaceColor', 'black');

I have not found anything on how to export shapes or how to rasterize them. Is there any way to do that?

Answer 1

Run the following code after yours.

imgwidth = max(1, ceil(max(x) - min(x)));
imgheight = max(1, ceil(max(y) - min(y)));
ax = gca;
ax.Visible = 'off';
ax.XTickMode = 'manual';
ax.YTickMode = 'manual';
ax.ZTickMode = 'manual';
ax.XLimMode = 'manual';
ax.YLimMode = 'manual';
ax.ZLimMode = 'manual';
ax.Position = ax.OuterPosition;
af = gcf;
figpos = getpixelposition(af);
resolution=get(0, 'ScreenPixelsPerInch');
set(af, 'paperunits','inches', ....
    'papersize',[imgwidth imgheight]/resolution, ....
    'paperposition',[0 0 [imgwidth imgheight]/resolution]);
print(af,'out.png','-dpng',['-r',num2str(resolution)],'-opengl')

Things done:

• Fetch data range and convert to image dimensions.
• Turn off axes and ticks.
• Minimize/remove padding space surrounding the actual content.
• Map 1 unit in data into 1 pixel in output image.

Things not done:

• Guarantee aspect ratio. (should work, though)

This screenshot shows non-unity aspect ratio output:

References

Mathworks - Save Figure at Specific Size and Resolution

MATLAB Central - saving a figure at a set resolution

Mathworks - print

Mathworks - Save Figure with Minimal White Space