MATLAB: Saving an image using ‘imwrite’

image processingsave

I'm trying to save an grayscale image to a file using

imagesc(Nv)
imwrite(Nv,'C:\Users\bostock_h\Documents\Images\chargemap.jpg')

but for some reason this just creates a file which is just white with the wrong dimensions. But I know 'Nv' is fine because the 'imagesc' brings up the image in MATLAB and it is correct.

Best Answer

imagesc() automatically scales data so that the minimum value maps to the first color and the maximum value maps to the last color. If your data does not happen to be in the range 0 to 1 for floating point values, or 0 to 255 for uint8, or 0 to 65535 for uint16, then the image that imwrite() creates is not going to be the image you want.

Related Solutions

MATLAB: White 256×256 image gives me 256x256x3

Try this:

whiteImage = 255 * ones(256, 256, 'uint8');
imwrite(whiteImage, 'White Image.png'); % Save to disk.

MATLAB: Using imwrite() to create a .bmp file with custom colormap

The colormap for the imwrite must be in the range 0 to 1.

When you imwrite with a colormap the data must be integral. If it is type double or single then 1 is subtracted from it and the result is converted to uint8. In other words the values must already be colormap indices.

You need:

Numcolor = size(myMap, 1);
Imgmin = min(MyImage(:)) ;
Imgmax = max(MyImage(:)) ;
mappedImage = uint8( (MyImage-Imgmin)./(Imgmax-ImgMin).* (Numcolor-1) ) ;

Then imwrite(mappedImage, myMap,...)

Best Answer

Related Solutions

MATLAB: White 256×256 image gives me 256x256x3

MATLAB: Using imwrite() to create a .bmp file with custom colormap

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