About quantization of image

i am trying to do uniform quantization on a gray scale image. i have to generate different images matrix for different K levels using imquantize() function and display all images. please let me know how to do that in MATLAB

[Geoff Hayes]

sweta - have you looked at the examples from imquantize?

[sweta arya]

yes,they only display images like one image for 256 level,then one for 16 levels.but i want images for all 16 levels,if my image is quantizing to 16 levels.

Answer 1

[Image Analyst]

Put it in a for loop

grayImage = imread('coins.png');
% Split the image into eight levels by obtaining seven thresholds from multithresh.
for numLevels = 1 : 16
  thresh = multithresh(grayImage, numLevels);
  % Construct the valuesMax vector such that the maximum value
  % in each quantization interval is assigned to the eight levels of the output image.
  valuesMax = [thresh max(grayImage(:))]
  [quant8_I_max, index] = imquantize(grayImage,thresh,valuesMax);
  valuesMin = [min(grayImage(:)) thresh]
  quant8_I_min = valuesMin(index);
  
  % Display both eight-level output images side by side.
  figure;
  imshowpair(quant8_I_min,quant8_I_max,'montage')
  title('Minimum Interval Value           Maximum Interval Value')
  % Set up figure properties:
  % Enlarge figure to full screen.
  set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
  % Get rid of tool bar and pulldown menus that are along top of figure.
  set(gcf, 'Toolbar', 'none', 'Menu', 'none');
  % Give a name to the title bar.
  set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')
end

Answer 2

[Ashish Uthama]

"i want images for all 16 levels"

I interpreted it as - quantize to 16 levels and give me a mask for each of those levels. (Though, now I think IA's answer above might be what you were looking for).

 im = magic(5);
 lvls = multithresh(im,3);
 qm = imquantize(im,lvls)

qm =

     3     4     1     2     3
     4     1     1     3     3
     1     1     2     4     4
     2     2     4     4     1
     2     3     4     1     2

imlvl1 = false(size(im));
% Replace 1 with any of the resulting 4 levels
imlvl1(qm==1)= true

imlvl1 =

     0     0     1     0     0
     0     1     1     0     0
     1     1     0     0     0
     0     0     0     0     1
     0     0     0     1     0