Sebastian Haase wrote:

Hi, I just was hunting a very strange bug: I got weird results .... anyway.

I found that I was using this line of code: if img.type() in (na.Complex64, na.Complex32): img = abs(na.asarray(img, na.Float32))

Now I don't understand how this code worked at all ? But I only saw those "weird results" after looking at the "dimmest corners" in my image and otherwise all images looked O.K.

The goal here was to get a single precision absolute for either a complex64 or complex32 valued image array WITHOUT creating a temporary array.

This idea sounds inconsistent to me. If the array is Complex64 and you pass it into asarray(,Float32), you're going to get a temporary. AND you're also truncating the imaginary part as you downcast to Float32... you're not getting a complex magnitude. Since abs() transforms from complex to real, you're going to get a temporary unless you get a little fancy, maybe like this: na.abs(img, img.real) # stores the abs() into the real component of the original array. img.real is a view not a copy. img.imag = 0 # optional step which makes the complex img array a real valued array with complex storage. img = img.real # just forget that img is using complex storage. Note that img is now discontiguous since no copy was made and there are still interleaved 0-valued imaginary components. So, I think there are two points to avoiding a copy here: (1) use the optional ufunc output parameter (2) store the abs() result into the .real view of the original complex array.

My thinking was that: img = na.abs( na.asarray(img, na.Complex32) ) would create a complete temporary version of img starts out being Complex64 Is this really the case ?

Yes.