Saving images using imwrite MATLAB

Question

I've an indexed image that is being saved in axes MATLAB GUI

file = 'C:\Documents and Settings\Home\Desktop\new.bmp';
        imwrite(handles.fname, file);
        imfinfo(file)

handles.fname has indexed image. above code saves image to desktop in BMP format with 24 bit depth. But i need to save in 8 bit-depth. what changes should i do in code?

Answer 1

After checking imwrite more closely found that the write option 'bitdepth' is not supported for BMP.

For conversion to 8-bit monochrome (see for instance here ) you can try

imwrite(rgb2gray(im2uint8(handles.fname)), file)

There are other ways of converting to monochrome other than rgb2gray , which uses the luminance channel.

If you want to reduce the color depth there is a link here that explains how you can achieve that with

new_4bit=uint8(16*(round((double(original)+1)/16)-1));
new_3bit=uint8(32*(round((double(original)+1)/32)-1));

This assumes original is a type uint8 image.

edit

I removed uint8 conversion statements. Before performing such operations one should check whether an image is type double or uint8, and scale values as necessary. I added im2uint8 which accomomdates different input data types.

Answer 2

This code is used to divided image in multiple images parts and save into disk reference link

% clc;    % Clear the command window.
% close all;  % Close all figures (except those of imtool.)
% Read the image from disk.
rgbImage = imread('image1.jpeg');
% Test code if you want to try it with a gray scale image.
% Uncomment line below if you want to see how it works with a gray scale image.
% rgbImage = rgb2gray(rgbImage);
% Display image full screen.
imshow(rgbImage);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
drawnow;
% Get the dimensions of the image.  numberOfColorBands should be = 3.
[rows, columns, numberOfColorBands] = size(rgbImage);
%==========================================================================
% The first way to divide an image up into blocks is by using mat2cell().
blockSizeR = 128; % Rows in block.
blockSizeC = 128; % Columns in block.
% Figure out the size of each block in rows.
% Most will be blockSizeR but there may be a remainder amount of less than that.
wholeBlockRows = floor(rows / blockSizeR);
blockVectorR = [blockSizeR * ones(1, wholeBlockRows), rem(rows, blockSizeR)];
% Figure out the size of each block in columns.
wholeBlockCols = floor(columns / blockSizeC);
blockVectorC = [blockSizeC * ones(1, wholeBlockCols), rem(columns, blockSizeC)];
% Create the cell array, ca. 
% Each cell (except for the remainder cells at the end of the image)
% in the array contains a blockSizeR by blockSizeC by 3 color array.
% This line is where the image is actually divided up into blocks.
if numberOfColorBands > 1
    % It's a color image.
    ca = mat2cell(rgbImage, blockVectorR, blockVectorC, numberOfColorBands);
else
    ca = mat2cell(rgbImage, blockVectorR, blockVectorC);
end
% Now display all the blocks.
plotIndex = 1;
numPlotsR = size(ca, 1);
numPlotsC = size(ca, 2);
for r = 1 : numPlotsR
    for c = 1 : numPlotsC
        fprintf('plotindex = %d,   c=%d, r=%d\n', plotIndex, c, r);
        % Specify the location for display of the image.
        subplot(numPlotsR, numPlotsC, plotIndex);
          % Extract the numerical array out of the cell
          % just for tutorial purposes.
          rgbBlock = ca{r,c};
          imshow(rgbBlock);
          %write images
          imwrite(rgbBlock,plotIndex+"_image.jpeg");
          % Could call imshow(ca{r,c}) if you wanted to.
          [rowsB columnsB numberOfColorBandsB] = size(rgbBlock);
          % Make the caption the block number.
          caption = sprintf('Block #%d of %d\n%d rows by %d columns', ...
              plotIndex, numPlotsR*numPlotsC, rowsB, columnsB);
          title(caption);
          drawnow;
          % Increment the subplot to the next location.
          plotIndex = plotIndex + 1;
           %imwrite(rgbBlock,c+"_image.jpeg");
    end
end
  



% Display the original image in the upper left.
%subplot(4, 6, 1);
%imshow(rgbImage);
%title('Original Image');
% Inform user of next stage where we process a gray scale image.
promptMessage = sprintf('Now I will do the same for a gray scale image.');
titleBarCaption = 'Continue?';
button = questdlg(promptMessage, titleBarCaption, 'OK', 'Cancel', 'OK');
if strcmpi(button, 'Cancel')
    return;
end