Re: Alternative pixel-based regtest checker

[David Kastrup]

Werner LEMBERG <address@hidden> writes:

>> I know from my Windows pixel-based checker that, generally, the PNG
>> files contain the same image, version after version (there are a few
>> oddities with some text, which I'm used to).  I would have believed
>> that identical images would only be produced by identical PNG files?
>
> Usually, picture container formats like PNG also contain metadata like
> the date of image creation or a comment.  This makes PNGs different
> even in case the contained images are identical.

Also they are compressed, and even with lossless compression, there is
more than one valid representation for most data.

However, if there is no time stamp in the image data and the image is
created by the same software, chances are that a byte-by-byte comparison
will largely reduce the amount of data one has to compare more
carefully.

-- 
David Kastrup