[Image-SIG] open, show, png, blank

[Nelson Tong]

>>
>> On 2/4/12, Randolph Bentson <bentson at holmsjoen.com> wrote:
>> > Oh, I guess the lambda function should be generalized by
>> >
>> > (lo,hi) = outI.getextrema()
>> > x = 256.0/(hi-lo)
>> > y = (0-lo)/256.0
>> > outJ = outI.point(lambda i:i*x+y)
>
> I have no experience with these type images, so I don't know if
> constant values are appropriate. The performance of the generalized
> mapping seems quick enough, so that may be safer.  BUT, there's
> one questionable issue with this function: it turns the darkest
> source pixel to black and the lightest pixel to white. I hope
> others can provide some comments on that.

I'm not an expert in image processing.  I just want to learn more
about this since we are talking about the mapping function here.

I don't quite completely understand how this generalized mapping
function work with im.point().  Given the hi and lo from getextema(),
I understand that x = 256.0/(hi-lo)
 is a way to  to adjust the scale parameter to the have a range of
values  from 0 to 256.  but where does the offset of (y= (0-lo) /256 )
comes from ? is there any reference anyone can recommend as a tutorial
about this kind of mapping function?








>
> --
> Randolph Bentson
> bentson at holmsjoen.com
>