Automatically picking bit-depth based on value seems dangerous, but a `guess_best_dtype(input_data: np.array) -> dtype` helper function would be useful. Tom On Fri, Mar 30, 2018 at 10:10 AM Gregory Lee <grlee77@gmail.com> wrote:

On Thu, Mar 29, 2018 at 1:46 PM, Juan Nunez-Iglesias <jni.soma@gmail.com> wrote:

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I think maybe 50% of our bug reports/help requests have to do with image data types. Does anyone want to express an opinion about how we can fix things?

My humble (really) suggestions, *to start* (ie more needs to be done than this):

* If a 16-bit or higher image has no values above 4096 or below 0, treat the image as 12 bit. This is a very common image type for some reason.

One common source for 12-bit is the DICOM standard used by industry for medical imaging.

* If an integer image has no values above 255, treat it as an 8-bit image.

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This also happens a lot.

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* If a floating point image has values outside [0, 1], don’t croak, just accept it. (This might have already happened?) If it has values only in [0, 1/255], and the user wants to convert to uint8, use the input range as the range.

I am in favor of accepting arbitrarily scaled floats unless the algorithm depends on values being within a particular range (not sure if we have many of these?). We do already allow unscaled floats in some places (e.g. compare_nrmse, etc), but it is not very consistent. For example, I recently noticed that denoise_wavelet enforces floats to be in [0, 1] (or [-1, 1]), but it would work equally well for unscaled data.

...

Some of these, especially the last one, may appear too magical, and in some ways I think they are, but honestly, given the frequency of problems that we get because of this, I think it’s time to suck it up and really work on doing what most of our users want most of the time. We don’t need to coddle the power users — they can be annoyed and micromanage the image range properly. To paraphrase a tweet I saw once (sorry, couldn’t find attribution): “edge cases should be used to check the design, not drive it.”

Applied to this case, we shouldn’t scale a uint32 image by 2**(-32) just because we can come up with a test case where this is useful.

Some of these problems would be alleviated by some consistent metadata conventions.

Juan.

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