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

[Randolph Bentson]

On Wed, Feb 08, 2012 at 02:31:37PM -0500, Nelson Tong wrote:
> Thanks Randolph.
> 
> this solution does indeed work for me.   The mapping function just
> manages to manipulate the pixel values enough so that png image can be
> opened  and be pasted onto other images without become blank.
> 
> lambda i:i * .0039062500 + 0
> 
> how important is the use of the generalized mapping function in here?
> does the  scale and offset of function definitely needs to be adjusted
> if every image I want to process is similar to each other in terms of
> min and max values?
> 
> 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.

-- 
Randolph Bentson
bentson at holmsjoen.com