Asymmetric behavior in dtype conversion

[Christoph Gohlke]

On 12/21/2011 8:41 AM, St�fan van der Walt wrote:
> On Wed, Dec 21, 2011 at 1:30 AM, Tony Yu<tsyu80 at gmail.com>  wrote:
>> I think one of two things should happen:
>>
>> 1)
>>      [uint ->  int]: expand uint to *full* range of int.
>>      [int ->  uint]: unchanged (squeeze into range of uint)
>>
>> 2)
>>      [uint ->  int]: unchanged (fill *positive* range of int)
>>      [int ->  uint]: clip negative values from int
> People very often represent images in signed integers, even though
> they only manipulate positive values, e.g. storing 0-255 in int8.  So
> the conversion to signed should not spread those values over the
> entire range.  However, I think you're right that we should add the
> clipping in 2 to avoid the conversion bias, along with a nice big
> warning.
>
> Regards
> St�fan
>

At this point it might be worth considering other cases that are 
currently not well handled by skimage dtype conversions. For example:

1) float images in the range 0.0 - 255.0
2) 1 bit images stored as (u)int
3) 10 and 12 bit images stored as uint16

Christoph