OpenEuphoria

Re: Scaling images

• Posted by Alexander Toresson <toressonodakra at swipnet.se> Nov 22, 2004
• 2334 views

Jonas Temple wrote:
> 
> Alexander Toresson wrote:
> > 
> > > Since graphics in Windows is my weak spot...how does one scale an image
> > > (BMP, PNG, JPEG, etc.) such that when the image is shrunk by the user
> > > it doesn't look funny?  What I mean by "funny" is that I have a window
> > > that displays an image (using FreeImage).  I want to show the image in
> > > the window for a "preview" so I use the stretchBlt function in 
> > > Win32Lib to shrink the image.  But the shrunken image does not look as
> > > good as say, shrinking the image in the Windows Picture and Fax Viewer in
> > > XP.
> > > 
> > > Can this be done with stretchBlt or is more complicated than that?
> > > 
> > 
> > Here's a way to do perfect scaling-down of images, using only a nearest-
> > neighbour scaling routine and a mosaic (square) effect:
> > 
> > You first have to scale the original picture up to make the width and 
> > height a multiple of the destination picture's size, and bigger than 
> > the original. Ie if the original is 1024x768, and the destination is 
> > 100x100, you'll have to scale it to 1100x800. For this operation,
> > linear interpolation helps, but ain't necessary.
> > 
> > Then we'll apply the mosaic effect, with a size of 
> > (width / dest_width)x(height / dest_height), in this example 11x8.
> > 
> > Then we just have to scale it down to the wanted size.
> > 
> 
> That all sounds good...I was hoping for a code example, though!  
> 
> Got one?   :)
> 

No, not at the moment. I'll code one. Anyway, I do not know the win32 api,
and doing it in eu may be too slow. I don't know if the win32 api
features a mosaic function. I'll code one 100% eu anyway.
I assume it's a 24-bit bitmap kept in a sequence, that is to be
processed.

/Lex

Shhh! Be vewy quiet! I'm hunting wuntime ewwows!