# Interpolating a zoomed in colorscale image in Matlab

• MATLAB
I have no idea what I am doing wrong. I have already found multiple places on the internet which give clear examples of how to do this, yet I am still struggling. Please help me out, or at least point me somewhere. My code is below. I am trying to interpolate pixels of a full color image. The only issue I am having is to display the final 3D matrix representing (what should be) a much clearer version of the original low quality image. During my troubleshooting, I tried displaying individual channels, yet was unable to (almost the entire image shows up as either red, green, or blue depending on which channel I attempted to display). However, displaying individual channels as 2D matrices (e.g. imagesc(newData(:, :, 1)) ) works albeit with an odd set of colors. I have verified in my workspace that the image pixels are being interpolated properly. The image I have been working with is attached.

function im = displayRGB(filename)
%obtain original picture and zoomed picture information
zoomData = imData(200:300,200:300,:);

%creating a grid corresponding to existing pixel values, as
% well as for pixel values to be interpolated
[height,width,dimension] = size(imData);
X = 1:width;
Y = 1:height;
[X0,Y0] = meshgrid(X,Y);
[X1,Y1] = meshgrid(200:.25:300,200:.25:300);

%interpolate each channel
newData = zeros(401,401,3);
newData(:,:,1) = interp2(X0,Y0,double(imData(:,:,1)),X1,Y1,'cubic');
newData(:,:,2) = interp2(X0,Y0,double(imData(:,:,2)),X1,Y1,'cubic');
newData(:,:,3) = interp2(X0,Y0,double(imData(:,:,3)),X1,Y1,'cubic');

%display the image
figure; imagesc(zoomData) %original zoomed image
figure; imagesc(newData) %clearer image

#### Attachments

• lab7_3.jpg
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Last edited:

Found it... apparently I needed to use newData = uint8(newData) before doing imagesc(newData). Not sure why at the moment (I had already tried using floor and ceiling functions to change the newData array values to integers).

You could cast it to uin8 but you don't need to if you don't want to. You can use colormaps with floating point arrays. Just use

Code:
imshow(yourDoubleArray, []);
colormap(jet(256)); % Or whatever colormap you want
colorbar;

You can mess around with caxis() if you want to apply the colormap to only a certain range of your data.