Description
Task 1 – Image Quantization
• myquantizer.m: takes a gray image and a target number of gray levels as
input, and generates the quantized image as output ;
• Note that, computers always represent “white” via the pixel value of
255(for uint8). For example, when “level” == 4, the resulting image
should contain pixels of {0, 85, 170, 255}, instead of {0, 1, 2, 3}.
• Sample: out_img = myquantizer(img, 4);
Task 1 – Image Quantization
2
4
8
32
128 Original: 256
Task 2 – Image Rescaling
• myscaler.m: takes a gray image and a target size as input, and generates
the scaled image as output;
• The new size may not be strictly larger or smaller than the original size.
That is, the case that 200×300 -> 100×400 will exist;
• Interpolation: nearest, bilinear, bicubic, …
• Sample: out_img = myscaler(img, [100, 400]);
• out_img = myscaler(img, [250, 255]);
Task 2 – Image Rescaling
300×450 200×500
200×300 128×192 64×96 32×48 16×24 8×12
Original: 384×256
Task 2 –
Image Rescaling
• Forward mapping
• Iterate over source, sending pixels to destination
• Holes may be generated during construction since
some points in the target image may not be hit.
• Reverse mapping
• Iterate over destination, finding pixels from
source.
• Non-integer coordinates: interpolation (Nearest,
Bilinear, Bicubic…)
• No holes, better than forward mapping
Task 2 –
Image Rescaling
Task 3 – Edge Detection in the Spatial Domain
• mysobeledge.m: computes the binary edge image from the input image;
• T = Threshold for generating the binary output image. If you do not
specify T, or if T is empty ([ ]), mysobeledge(img,[],direction) chooses the
value automatically according to Algorithm 1 described in the
assignment handout.
• direction = A string for specifying whether to look for ‘horizontal’ edges,
‘vertical’ edges, positive 45 degree ‘pos45’ edges, negative 45 degree
‘neg45’ edges, or ‘all’ edges (maximum of all responses).
Octave – Description
Octave – Description
Octave – Difference
Image Processing in Matlab/Octave
Image Processing in Matlab/Octave
im2double
Image Processing in Matlab/Octave
clc
clear
img = imread(‘example_1.png’);
% Pay attention that the data type of matrix img is
uint8
imshow(img)
% Now we change it to double(Why?)
img = double(img);
%img = im2double(img);
%{
% Why do we need transfer to double?
img = imread(‘example_1.png’);
img = img + 2;
img = img * 2;
img = imread(‘example_1.png’);
img = double(img);
img = img * 2;
%}
img_inv = 255 – img;
img_log = 30 * log(1 + img);
img_pow = 0.1 * img.^1.5; % A * B ~= A .* B (*, /, ^,
…) c * img^n
img_con = (img > 100) * 255; % img > 100: logical matrix
%{
% Why do we need transfer to uint8?
img_inv = uint8(img_inv);
img_log = uint8(img_log);
img_pow = uint8(img_pow);
img_con = uint8(img_con);
%}
subplot(221),imshow(img_inv,[]),title(‘Inverse’)
subplot(222),imshow(img_log,[]),title(‘Log’)
subplot(223),imshow(img_pow,[]),title(‘Power’)
subplot(224),imshow(img_con,[]),title(‘Contrast
Stretching’)
%{
% mat2gray
img = imread(‘example_1.png’);
img = double(img);
img = img * 2;
img = mat2gray(img);
%}
Vectorization
Assignment Submission and Marking
1. Your submitted programs should be myquantizer, myscaler, and mysobeledge,
plus all the other related M-files (plus README.txt file).
2. You must include a README.txt file indicating the programming software
(Octave or MATLAB) that you are using for this assignment. By default, we will
grade your assignment with Octave if the README.txt file is missing.
3. Please also attach your stitching results for different groups of images when
you submit the codes. If there are more than two images in the group, then your
result image should be the stitching results for all the images within the group.
Assignment Submission and Marking
4. You must compress all your files with the following filename format: [your 8-digit student ID]_assign1.rar (or
zip), e.g. 09654321_assign1.rar, into one file.
5. If your assignment compressed file has been submitted multiple times before the due date (including late
submission date), the new version will replace the old version in marking.
6. Note that we take plagiarism seriously. You are allowed to discuss or share your idea to your classmate, but
you are not allowed to share your code/pseudocode of your assignment. Please also follow the referencing
skills at https://libguides.ust.hk/referencing/plagiarism to avoid plagiarism.
7. Marks would be deducted if there are any violations of the above requirements.
Octave package installation
If you are using Octave, you need to install the image package.
>> pkg install -forge image
And load the image package by
>> pkg load image
