how to convert 24bit of bmp image to 8 bit?

i tried to make this program :

I = imread ('ctv.bmp');
kernel1 = [ -1 -1 -1 ; -1 8 -1 ; -1 -1 -1 ]
kernel2 = [ -1 -1 -1 ; -1 9 -1 ; -1 -1 -1 ]
kernel3 = [ 1/9 1/9 1/9; 1/9 1/9 1/9; 1/9 1/9 1/9 ]  
hiPass = conv2(I, kernel1);
lowPass = conv2(I, kernel3);
bandPass = conv2(I, kernel2);
subplot(2,2,1), imshow(I);title('Gambar Asli');
subplot(2,2,2), imshow(uint8(hiPass));title('HiPass');
subplot(2,2,3), imshow(uint8(lowPass));title('LowPass');
subplot(2,2,4), imshow(uint8(bandPass));title('BandPass');

but it couldn't run. how to convert the 24bit to 8bit image?

Answer 1

[Stephen23]

Here is the official MATLAB answer:

http://www.mathworks.com/matlabcentral/answers/93196-how-do-i-convert-a-24-bit-depth-image-file-to-an-8-bit-depth-image-file

Or doing a search of this forum brings up lots of answers:

http://www.mathworks.com/matlabcentral/answers/108731-how-to-convert-24-bit-depth-images-into-8-bit-depth-and-16-bit-depth-images

[fk]

thank you for your help :D btw, i've found another way to change it to 8 bit. just convert the image to .gif because .gif is only in 8 bit. FYI :D