Spray painting simulation and thickness evaluation

I want to simulate a spray painting, like a “brushes” in “paint” program, by using the left mouse.

The idea is that when I click and hold the left mouse, color is continuously sprayed and its coating stroke is uniformed. The thickness is reflected through color intensity

[Image Analyst]

What kind of measurement? What is a strake? Any idea of how it can be measured? Do you have a digital image of it?

[Anh]

I want to simulate a spray painting, like a “brushes” in “paint” program, by using the left mouse. When I push the left mouse, color is sprayed and its coating stroke is uniformed. The thickness is reflected through color intensity.

[Image Analyst]

OK, I think you meant "stroke thickness setting". But I don't know how to do it. I'd just use Photoshop for something like that.

Answer 1

[Angelo Yeo]

Maybe some basic approach is to use a button down callback and scatter dots that are randomly sampled from normal distribution. Below is my simple implementation of the idea. Good luck.

clear; close all;
I = zeros(1000, 1000);
imagesc(1:1000, 1:1000, I, 'ButtonDownFcn', @sprayCallback);
clim([0, 1]);
colormap([1,1,1; 0,0,0])
axis([0, 1000, 0, 1000])
hold on;

function sprayCallback(h, ~)
cursorLocation = get(ancestor(h, 'axes'),'CurrentPoint');

x = cursorLocation(1, 1);
y = cursorLocation(1, 2);

radius = 30;

scatter(randn(100, 1) * radius + x, randn(100,1) * radius + y, 1, [0,0,0], 'filled', 's')
end

[Anh]

it doesn't work ~~

[Angelo Yeo]

Can you elaborate how you tried to run the script? What did you try and what error do you get?

[Anh]

I first tried running your code, but it displayed nothing.

When I clicked on the figure, the matlab command window showed the cursorLocation's values like this.

[Anh]

I found it, forgot to change the size of the plot.

[Angelo Yeo]

Strange. I ran the script in R2023b, and it works like below.

[Anh]

It works well. I just forgot to change the radius and size of the plot.

By the way, I want to ask if the is a function like "press" and "hold" in Matlab such that when I click and hold the left mouse, color is continuously uniform with its intensity change from light to dark. This will be exact what I want to do for the spray painting. And by evaluating the overlapped pixels, thickness can be measured relatively.