Overlaying thousands of images

[re-fuse]

hey all,

i have an 1D array with thousands of pictures and i want to overlay them all in one as fast as possible.

i've tried different approaches ... so far the best one i found is to use "concatenate strings" but still too slow for my need.

 anyone got any idea?

[zou]

The subVI you use (Draw Point.vi) is not a reentrant VI, so parallelism doesn't help.

How fast you need?

> i have an 1D array with thousands of pictures

Actually, that's 1D array of points, not pictures.

Why not use chart/graph ?

[re-fuse]

thx for the reply, zou!

good to know that parallelism doesnt work here ... it actually slows it down by a factor of 2 i've just realized.

> i have an 1D array with thousands of pictures

Actually, that's 1D array of points, not pictures.

Why not use chart/graph ?

yeah it's a 1d array of points ... but in pictures. so thousands of pictures with one black pixel each.

i know chart/graph would be way easier here ... but i've got to implement this in an already existing VI and everything that's graphic there is handled as a pattern image. besides i need to to export the pattern imager (respectively the 1d array of points) as *.bmp file

the pattern/picture i want to draw consist of e.g. 4.000.000 points (x/y coordinates).

so i need a way to draw all those points in one picture ... ideally in under 5minutes.

in my first version i overlayed picture by picture through a shift-register in the for-loop. that was way too slow.

[zou]

Put the content of the subVI in your VI.

Try the modified VI.

[altenbach]

How many colors are there? Initialize a 2D array of U8, then replace elements according to the coordinates. Create a color map that contains the 256 colors you have and form the image at the end using flatten pixmap. Or use draw unflattened pixmap directly if it is just for display! (You could even us an intensity graph!).

If you have more colors, do the same with U32.

Can you attach a VI that contains some typical inputs?

[altenbach · Accepted solution]

Here's what I had in mind....

 

Modify as needed. As I said, you can use draw unflattened pixmap to create an image from the result or add it to an existing image.

[perhult]

Same thought as Altenbach, but I add my snippet anyway since I also have some benchmark figures that might be interesting.

With 4 million points in a 4000*4000 image this took less than 30 s on my crappy laptop.

If your points are already ordered in some way it could be done my faster, I believe

[altenbach]

You are adding 4 million pixels (quite a few probably in duplicate), which is significantly more than "thousands". I would expect to solve original problem to be much, much  faster. (<<<1s) 😄

[perhult]

You are absolutely right, I got carried away and did not read the orginial post carefully so I mixed up the numbers. I agree, I tested it again and it will take in the order of 1/10 s

[altenbach]

Using an array of 4M coordinates on a 4kx4k array takes about 18ms here. Drawing the flattened pixmap is the slow step and takes hundreds of milliseconds. I would stay away from picture functions and use simple 2D arrays.