how to load multiple image files into matlab and save them as an animated gif

Question

I'm looking to load image files into Mat lab and save them all to an animated .GIF of a set speed. i have tried loading them in using imread() and mapping them with rgb2ind() then saving with the given imwrite() code from the website appending them to the file, i have errors when trying to use the rgb2ind() saying that i need a uint8 array or a 3Duint8 array when i try various things.

%arg 1 number of inputs
%arg 2 is speed
%arg[] files
function main(varargin)

num = str2num(varargin{1});
speed = str2double(varargin{2});

for i=1:num
a = imread(varargin{i+2});
[A map] = rgb2ind(a,256);
if i==1
   imwrite(A,map,'new.gif', 'gif','LoopCount',65535,'DelayTime',speed)
else
    imwrite(A,map,'new.gif', 'gif','WriteMode','append','DelayTime',speed)

end

end

I posted an answer based on an assumption that a = imread(varargin{i+2}); reads a Grayscale image. If this is not the case, please let me know (there is also a chance that your input images are [colored] indexed images, and your are not using imread correctly). — Rotem

Rotem Rotem · Accepted Answer · 2019-11-20T23:15:11

It's most likely that you are passing Grayscale as input image to rgb2ind.

Example for correct usage:

I = imread('peppers.png');
[A, map] = rgb2ind(I, 256);

Above sample loads image in RGB format and there is no error (peppers.png is RGB image).

Example that gives and error message:

I = imread('cameraman.tif');
[A, map] = rgb2ind(I, 256);

Result of above code:

Error using cq
First input must be a 3-D uint8 array.

Error in rgb2ind (line 93)
[map,X] = matlab.images.internal.cq(RGB,m);

The reason for the error is that cameraman.tif is a Grayscale image (and not RGB).

A quick fix is to convert Grayscale images to RGB format.
Converting Grayscale to RGB is done by duplicating the Grayscale three times (creating an RGB image with R=G=B for all pixels).

Here is a code sample that checks if image is in Grayscale format, and convert to RGB if needed:

I = imread('cameraman.tif');

%Check if I is Grayscale
if (size(I, 3) == 1)
    %Convert Grayscale to RGB by duplicating I three times.
    I = cat(3, I, I, I);
end

[A, map] = rgb2ind(I, 256);

The above code is executed successfully.

how to load multiple image files into matlab and save them as an animated gif

1 Answers