On Tue, Jul 25, 2006 at 07:03:34PM +0100, Reuben Thomas wrote:
> Package: libjpeg62
> Version: 6b-13
> Severity: normal
>
> I have a picture on which jpegtran -flip horizontal causes a few
> columns not to be flipped.
>
> The picture was produced by mogrify from a larger picture. For the
> moment, I attach just the smaller picture (bar.jpg) and its
> incorrectly flipped version (baz.jpg), but I can provide the larger
> original and mogrify command if that's useful.
Hello Reuben,
Your image size is 230x345. Please look at jpegtran manpage:
The transpose transformation has no restrictions regarding image dimen-
sions. The other transformations operate rather oddly if the image
dimensions are not a multiple of the iMCU size (usually 8 or 16 pix-
els), because they can only transform complete blocks of DCT coeffi-
cient data in the desired way.
jpegtran's default behavior when transforming an odd-size image is
designed to preserve exact reversibility and mathematical consistency
of the transformation set. As stated, transpose is able to flip the
entire image area. Horizontal mirroring leaves any partial iMCU column
at the right edge untouched, but is able to flip all rows of the image.
Similarly, vertical mirroring leaves any partial iMCU row at the bottom
edge untouched, but is able to flip all columns. The other transforms
can be built up as sequences of transpose and flip operations; for con-
sistency, their actions on edge pixels are defined to be the same as
the end result of the corresponding transpose-and-flip sequence.
This is what is happening here. I suggest you use either the -trim or
-perfect option, see the manual.
Cheers,
--
Bill. <[EMAIL PROTECTED]>
Imagine a large red swirl here.
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