regardless of image format.

In this post I'm talking about "SLC" data, i.e. complex data, in amplitude and phase. Phase is essential for correct resampling.

You'll need to transform it into an array (python, matlab, C...) of complex values.

Sometimes, certain .tiff files are able to handle the complex format either in a single "complex" band, or by using one band for the real part and another for the imaginary part. In png, this is much rarer, it seems to me...