I want to convert an input image into floating point, so that interpolation using interp2 will be possible. I want to achieve this without using the Image Processing Toolbox and without the im2double function. So I tried the syntax I=double(I), however, the resulting image looked very different than the original.
Here is a comparison of the resulting images using im2double(I) and double(I) respectively:
What is happening here? It looks like the double(I) code eliminates the higher frequencies from the spectrum of the image:
When I plot double(I) using imagesc instead of imshow I get the right image displayed, but the spectrum is still shrunken.
So, how can I implement what im2double does without using the pre-defined function? Any explanation is greatly appreciated.