MATLAB: How to flip an axis using imagesc

flip axisimage processingimagescMATLAB

I want to display the Matrix eta (7×16) by using the imagesc function. I use the code:

T=[360 660]
p=[64 250]
imagesc(T,p,eta)

which produces the follwing image:

Now I want to flip the y-axis so that 50 is at the bottom and 250 is at the top. The Image should flip as well. Using

eta=flipud(eta)
T=[360 660]
p=[64 250]
p=fliplr[p]
imagesc(T,p,eta)

doesn't work. Thank you!

Best Answer

Do you mean like with axis xy?

[x, y] = meshgrid(1:16, 1:7)
eta = uint8(rescale(sqrt(x.^2 + y.^2), 0, 255));
T=[360, 660];
p=[64, 250];
subplot(2, 1, 1);
imagesc(T,p,eta)
axis('on', 'image');
subplot(2, 1, 2);
imagesc(T,p,eta)
axis('on', 'image');
axis xy

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MATLAB: How to Detect Edges of an Image using Canny Edge Detection technique. I have already detected edges of Images, but I’m not sure if it is correct or not. Also, I want to add legend command and axis information in this, how would I do this thing

Use axis('on', 'image'). I fixed other problems too. Fixed code is below:

clc;
clear all;
close all;
workspace;  % Make sure the workspace panel is showing.
% Read in original RGB image.
rgbImage  = imread('Table.jpg');
subplot(2, 2, 1);
imshow(rgbImage)
axis('on', 'image');
title('Original Image')
% Convert to gray scale.
grayImage = rgb2gray(rgbImage);
subplot(2, 2, 2);
imshow(grayImage)
axis('on', 'image');
title('Grey Scale Image')
% Get edges
Canny_img = edge(grayImage, 'Canny');
subplot(2, 2, 3);
imshow(Canny_img, [])
axis('on', 'image');
title('Edge Detected Image')
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'Outerposition', [0, 0.05, 1, 0.95]);

By the way, you don't need to do edge detection to "find" the table if that's all that you want to do. You can simply threshold.

MATLAB: How to draw a Lab* colour space or HSV colour space (2D)

As commented in your question, note that you're only plotting one slice of the 3D colour space.

Of course, your original code doesn't work, you end up doing

pcolor(x, y, thg);

so you're only plotting the hue (angle) against x and y. There's no saturation or value information in your plot. You then apply a colour map called hsv whose colours are derived from the hsv cylinder, but in no way does it mean you've done any conversion to/from hsv. The whole idea is flawed.

Here is how I'd do it:

%inputs:
%plotradius: the plot radius of the disk. Image will be 2*plotradius+1 x 2*plotradius+1
%plotvalue:  the Value at which the slice of the HSV cylinder is to be taken. In the range 0-1
plotradius = 100;
plotvalue = 1;
[x, y] = meshgrid(-plotradius:plotradius);  %get x,y coordinates of pixels in image
[hue, saturation] = cart2pol(x, y);  %convert to angle, radius. Angle is the hue, radius is the saturation in the HSV cylinder
hue = (hue + pi) / (2*pi); %rescale from -pi:pi to 0:1 since matlab use 0:1 for the range of the hue
saturation = saturation / plotradius;  %rescale saturation to range 0:1. Not that anything above 1 is outside the cylinder
value = ones(size(hue)) * plotvalue;  %set value constant for all points in the disk
%now set points outside the disk (saturation >1) to white. That'd be a value of 1 and saturation of 0. hue doesn't matter
outsidedisk = saturation > 1;
saturation(outsidedisk) = 0;
value(outsidedisk) = 1;
%finally, convert hsv to rgb and plot
rgb = hsv2rgb(cat(3, hue, saturation, value));
imshow(rgb);

Best Answer

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MATLAB: How to Detect Edges of an Image using Canny Edge Detection technique. I have already detected edges of Images, but I’m not sure if it is correct or not. Also, I want to add legend command and axis information in this, how would I do this thing

MATLAB: How to draw a L*a*b* colour space or HSV colour space (2D)

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MATLAB: How to draw a Lab* colour space or HSV colour space (2D)