good evening , iam getting error as (im2jpeg(x, quality) Error using im2jpeg (line 21) The input must be a UINT8 image) at line 21 . how can i resolve it in the below code

function y = im2jpeg(x, quality)
%IM2JPEG Compresses an image using a JPEG approximation.
% Y = IM2JPEG(X,QUALITY) compresses image X based on 8x8 DCT transforms,
% coefficient quantization, and Huffman symbol coding. Input QUALITY  
% determine the amount of information that is lost and compression
% achieved. Y is an encoding structure containing fields:
%   Y.size         Size of X
%   Y.numblocks    Number of 8-by-8 encoded blocks
%   Y.quality      Quality factor as percent
%   Y.huffman      Huffman encoding structure, as returned by MAT2HUFF
%
%   See also JPEG2IM

% Define recursion maximum values;
error(nargchk(1,2,nargin));            % Check input arguments
if (~ismatrix(x)) || ~isreal(x) || ~isnumeric(x) || ~isa(x, 'uint8')
    error('The input must be a UINT8 image');
end
if nargin<2
    quality = 1;            % Default value for quality
end
if quality>1                % Check allowable values for qualiity
    quality =1;
    disp('WARNING: !!! Allowable values of quality in the range [0.1 1]. Quality set to 1 !!!');
elseif quality<0.1 
    quality =0.1;
    disp('WARNING: !!! Allowable values of quality in the range [0.1 1]. Quality set to 0.1 !!!');
end
m =[16 11 10 16 24 40 51 61     % JPEG normalizing array
    12 12 14 19 26 58 60 65     % and zig-zag reordering
    14 13 16 24 40 57 69 56     % pattern
    14 17 22 29 51 87 80 62
    18 22 37 56 68 109 103 77
    24 35 55 64 81 104 113 92
    49 64 78 87 103 121 120 101
    72 92 95 98 112 100 103 99];

m = ceil(m/(2*quality));

order = [1 9  2  3  10 17 25 18 11 4  5  12 19 26 33 41 ...
        34 27 20 13 6  7  14 21 28 35 42 49 57 50 43 36 ...
        29 22 15 8  16 23 30 37 44 51 58 59 52 45 38 31 ...
        24 32 39 46 53 60 61 54 47 40 48 55 62 63 56 64];

[xm, xn] = size(x);              % Get input size.
x = double(x) - 128;           % Level shift input  
t = dctmtx(8);                   % Compute 8x8 DCT matrix

% Compute DCTs of 8x8 blocks and quantize the coefficients.
y = BLKPROC(x, [8 8], 'P1 * x * P2', t, t');
y = BLKPROC(y, [8 8], 'round(x./P1)',m);

y = im2col(y, [8 8], 'distinct');   % Break 8x8 block into columns

% DPCM on DC coefficients
DCcoeff = y(1,:);
DCcoeff = [DCcoeff(1) diff(DCcoeff)];
y(1,:) = DCcoeff;

xb = size(y, 2);                    % Get number of blocks
y = y(order,:);                     % Reorder column elements
eob = max(y(:)) + 1;                % Create end-of-block symbol
%eob = -256;
r = zeros(numel(y) + size(y,2), 1);
count = 0;
for j = 1:xb                % Process 1 block (col) at a time
    i = find(y(:,j), 1, 'last' );  % Find the last non-zero element
    if isempty(i)           % No nonzero block values
        i=0;
    end
    p = count +1;
    q = p + i;
    r(p:q) = [y(1:i,j); eob];   % Truncate trailing 0's, add EOB
    count = count + i + 1;      % and add to output vector
end
r((count + 1):end) = [];        % Delete unused portion of r
clear y;
y.size      = uint16([xm xn]);
y.numblocks = uint16(xb);
y.quality   = uint16(quality*100);
y.huffman   = mat2huff(r);

Answer 1

[dpb]

The problem isn't in the code in the function, it's in what you're passing to it as an input image. The function is written to only work(*) on 8-bit image data of uint8 class.

You didn't show how you got the data and called the function; there's where you need to look.

(*) Not to say it might not be able to be expanded to use other numeric classes, but that's what it's written for explicitly and to do other would take reading the code thoroughly enough to understand what and how to make changes for other classes. It might be simple, might be difficult; might even be just inherent that it only makes sense for uint8; that I haven't tried to discern.