Using rgb2ind for colour animated gif

I have a workaround but this is a request for something more elegant.

I'd like to write a colour animated gif from a series of images (not captured from a figure window, although this is still applicable).

to ensure my colour images are not converted to indexed greyscale I have to "stitch" all the frames into a single image, then run rgb2ind to obtain the optimised colormap for all images in the sequence. Then I convert all individual frames to indexed colour using rgb2ind and then finally use imwrite to save the gif:

a=imread('frame1.jpg']);
b=imread('frame2.jpg']);

temp=[a;b];

[~,map]=rgb2ind(temp,256);

c(:,:,:,1)=rgb2ind(a,map);
c(:,:,:,2)=rgb2ind(b,map);

Error using matlab.internal.lang.capability.Capability.require
This functionality is not available on remote platforms.

Error in implay (line 51)
matlab.internal.lang.capability.Capability.require(...

 

imwrite(c,map,'myGif.gif','Loopcount',inf,'DelayTime',0.5)

So the requests are:

• Is there a more elegant way of doing this that I'm missing?
• Can rgb2ind be made to work with 4D (or indeed any dimension) of array? it's just a bunch of numbers after all...
• Can imwrite have a colormap switches for gifs like 'colormap', 'optimise'?

Answer 1

[DGM]

I posted this already as a comment in the other thread, but I'll put it here too:

MIMT gifwrite() works to write I/IA/RGB/RGBA and indexed color images from 4D arrays. MIMT gifread() can read the image with minimal hassle.

https://www.mathworks.com/matlabcentral/fileexchange/52514-tools-to-read-and-write-animated-gif-files

Pay attention to the synopsis if you intend to read GIF files in versions newer than R2018a -- regardless of what tools you're using. If you're using a newer version, you will not be able to correctly read most multiframe color GIF files unless you make that effort.

Stitching the frames together to generate a colormap is a bad idea, since it means that no frame can have a unique optimized local color table. The more dynamic the color content is over the sequence, the worse the entire image will look.

If you don't use third-party tools like those to do the job, the canonical way to do this with imwrite() is tedious. That's just the way it is. You would have to write a loop and quantize each frame individually if you want good color range. The same goes for reading the file.