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Re: Backend and non-backend (was Re: Stencil bounding box)

From: Johannes Schindelin
Subject: Re: Backend and non-backend (was Re: Stencil bounding box)
Date: Tue, 2 May 2006 21:29:39 +0200 (CEST)


On Tue, 2 May 2006, David Feuer wrote:

> On 5/1/06, Johannes Schindelin <address@hidden> wrote:
> > You cannot just compare PNGs. The really important information is: where
> > is the object, not: what color is that pixel. Just think about the
> > consequences of a small adjustment of the position. The difference of the
> > PNGs is potentially quite large, even if the difference of the location is
> > quite small.
> I'm not convinced.  What if you apply a slight blur to both images and
> then subtract them?


The thing is that you don't know what caused the difference when just 
subtracting them. For example, it is an error if a half note is printed 
instead of a quarter note, but the difference can be smaller than if the 
quarter note is shifted (for example to avoid a clash).


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