EFFECT OF VARYING NUMBER OF SAMPLES ON IMAGE QUALITY LAKSHMI.M M.E, COMMUNICATION SYSTEMS
Jun 11, 2015
EFFECT OF VARYING NUMBER OF SAMPLES ON
IMAGE QUALITY
LAKSHMI.MM.E, COMMUNICATION SYSTEMS
SAMPLING
Sampling is the first operation done in digitalization of an analog signal followed by quantization
Sampling - principal factor determining the spatial resolution of an image.
Spatial resolution is the smallest discernible detail in an image.
SAMPLING
UPSAMPLING- INCREASING THE NUMBER OF SAMPLES
DOWNSAMPLING- DECREASING THE NUMBER OF SAMPLES
Upsampling and Downsampling of a discrete signal
CODE FOR DOWNSAMPLING:
clc;clear all;close all;f=imread('cameraman.tif'); y=imresize(f,[1024 1024]); figure; imshow(y); down=y(1:2:end,1:2:end); figure; imshow(down); down1=y(1:4:end,1:4:end); figure; imshow(down1); down2=y(1:8:end,1:8:end); figure; imshow(down2); down3=y(1:16:end,1:16:end); figure; imshow(down3); down4=y(1:16:end,1:16:end); figure; imshow(down4);
Fig1.1024*1024
Fig2. 512*512
Fig3. 256*256
Fig4. 128*128
Fig5. 64*64
Fig6. 32*32
DOWNSAMPLED IMAGES
EFFECT OF VARYING NUMBER OF SAMPLES
256*256 256*256
Downsampled by a factor of 3
Upsampled by a factor of 3
clc;clear all;close all;f=imread('cameraman.tif'); y=imresize(f,[8 8]);figure; imshow(y);disp(y);display('size of original image:');l1=size(y);disp(l1); %downsamplingdown=y(1:2:end,1:2:end);disp(down);display('size of downsampled image:');l2=size(down);disp(l2);figure; imshow(down);
Upsampling the downsampled image
% upsampling the downsampled image up=down(1:0.4:end,1:0.4:end);disp(up);display('size of upsampled image:');l3=size(up);disp(l3);figure; imshow(up);
Pixel values of original image
EFFECT OF VARYING NUMBER OF SAMPLES
256*256 256*256
Upsampled by a factor of 3
Downsampled by a factor of 3
f=imread('cameraman.tif'); y=imresize(f,[4 4]);display('pixel values of original image');figure; imshow(y);title('original image');disp(y);display('size of original image:');l1=size(y);disp(l1);%upsamplingup=y(1:0.4:end,1:0.4:end);display('pixel values of downsampled image');disp(up);display('size of upsampled image:');l2=size(up);disp(l2);figure; imshow(up);title('upsampled image');
Downsampling the upsampled image
%downsampling the upsampled imagedown=up(1:2:end,1:2:end);display('pixel values of reconstructed image');disp(down);display('size of reconstructed image:');l2=size(down);disp(l2);figure; imshow(down);
Inference:
Downsampling provides reduced pixel value image which when zoomed, results in poor image quality
In upsampling, no pixel value is removed and hence when downsampled to its original image size, almost the original image quality is obtained.
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