Read image and display it.

I = imread('circlesBrightDark.png'); imshow(I) axisofftitle('Original Image')

Calculate two threshold levels.

thresh = multithresh(I,2);

Segment the image into three levels usingimquantize.

seg_I = imquantize(I,thresh);

Convert segmented image into color image usinglabel2rgband display it.

RGB = label2rgb (seg_I);图;imshow (RGB)轴offtitle('RGB Segmented Image')

Read truecolor (RGB) image and display it.

I = imread('peppers.png'); imshow(I) axisofftitle('RGB Image');

Generate thresholds for seven levels from the entire RGB image.

threshRGB = multithresh(I,7);

Generate thresholds for each plane of the RGB image.

threshForPlanes = zeros(3,7);fori = 1:3 threshForPlanes(i,:) = multithresh(I(:,:,i),7);end

Process the entire image with the set of threshold values computed from entire image.

value = [0 threshRGB(2:end) 255]; quantRGB = imquantize(I, threshRGB, value);

Process each RGB plane separately using the threshold vector computed from the given plane. Quantize each RGB plane using threshold vector generated for that plane.

quantPlane = zeros( size(I) );for我= 1:3价值=[0刺hForPlanes(i,2:end) 255]; quantPlane(:,:,i) = imquantize(I(:,:,i),threshForPlanes(i,:),value);endquantPlane = uint8(quantPlane);

Display both posterized images and note the visual differences in the two thresholding schemes.

imshowpair(quantRGB,quantPlane,'montage') axisofftitle('Full RGB Image Quantization Plane-by-Plane Quantization')

To compare the results, calculate the number of unique RGB pixel vectors in each output image. Note that the plane-by-plane thresholding scheme yields about 23% more colors than the full RGB image scheme.

dim = size( quantRGB ); quantRGBmx3 = reshape(quantRGB, prod(dim(1:2)), 3); quantPlanemx3 = reshape(quantPlane, prod(dim(1:2)), 3); colorsRGB = unique(quantRGBmx3,'rows'); colorsPlane = unique(quantPlanemx3,'rows'); disp(['Unique colors in RGB image : 'int2str(length(colorsRGB))]);

Unique colors in RGB image : 188

disp(['Unique colors in Plane-by-Plane image : 'int2str(length(colorsPlane))]);

Unique colors in Plane-by-Plane image : 231

Reduce the number of discrete levels in an image from 256 to 8. This example uses two different methods for assigning values to each of the eight output levels.

Read image and display it.

I = imread('coins.png'); imshow(I) axisofftitle('Grayscale Image')

Split the image into eight levels by obtaining seven thresholds from multithresh.

thresh = multithresh(I,7);

Construct thevaluesMaxvector such that the maximum value in each quantization interval is assigned to the eight levels of the output image.

valuesMax = [thresh max(I(:))]

valuesMax =1x8 uint8 row vector65 88 119 149 169 189 215 255

[quant8_I_max, index] = imquantize(I,thresh,valuesMax);

Similarly, construct thevaluesMinvector such that the minimum value in each quantization interval is assigned to the eight levels of the output image. Instead of callingimquantizeagain with the vectorvaluesMin, use the output argument index to assign those values to the output image.

valuesMin = [min(I(:)) thresh]

valuesMin =1x8 uint8 row vector23 65 88 119 149 169 189 215

quant8_I_min = valuesMin(index);

Display both eight-level output images side by side.

imshowpair(quant8_I_min,quant8_I_max,'montage') title('Minimum Interval Value Maximum Interval Value')