[Zope] Photo: somes issues and thoughts

[J M Cerqueira Esteves]

* J M Cerqueira Esteves <jmce@artenumerica.com> [2002-01-03 19:40 +0000]:
> Unfortunately, I had no time to determine the precise equation used
> by ImageMagick to calculate new sizes maintaining aspect ratio.
> Having it, you could use that instead of the calculation at
> _getAspectRatioSize when resizing with PIL (since PIL's `resize',
> unlike ImageMagick's `convert', doesn't try to maintain aspect ratio
> and needs to be given precise final sizes).

I have just found what ImageMagick uses, in magick/image.c, function
ParseImageGeometry.  If (w0, h0) are the original width and height and
(wM, hM) are the maximum width and height allowed (specified with
-geometry wMxhM), ImageMagick defines the final width and height
as follows (in Python):

  scale = min (float (wM) / w0, float (hM) / h0)
  width = max (int (scale * w0 + 0.5), 1)
  height = max (int (scale * h0 + 0.5), 1)

while Photo uses (with integer division, therefore with truncation everywhere):

  if hM > h0 * wM / w0:
    height = h0 * wM / w0
    width = wM
  else:
    height = hM
    width =  w0 * hM / w0