[Bins] Bug in image conversion?
bins_album at oxstone.com
Sat Feb 26 02:05:33 GMT 2005
On Mon, Feb 21, 2005 at 04:38:14PM -0500, Daniel Martin wrote:
> Nicolas <bins_album at oxstone.com> writes:
> > Hello,
> > When I look at my galleries, I can sometimes see like a bug on the
> > scaled pictures. Look at there:
> > http://www.europephoto.com/moto/200502/20050220_Ballade_Repaire_Peters/dsc_0757_Pt.jpg.2.html
> > The picture right border seems to come from the left border of the
> > picture!
> I believe that this feature is a consequence of how bins uses
> jpegtran; basically, jpegtran has funny behavior when rotating images
> with dimensions are not an even multiple of the jpeg compression block
> size, usually 8 or 16 pixels.
> Quoting from the jpegtran manpage:
> 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 consistency, their actions on
> edge pixels are defined to be the same as the end result of the
> corresponding transpose-and-flip sequence.
> A 90-degree right rotation is represented as transpose followed by
> horizontal flip - you'll notice that the extra strip on the right of
> the image is not only taken from the lhs of the image but also is
> reversed left-to-right.
> So the way out of this? Three ways I can think of:
> 1. Don't use jpegtran to rotate images (that's part of the config.),
> 2. apply jpegtran only to properly sized images by setting explicit
> sizes within bins so that every image that bins rotates will be a nice
> size, OR
> 3. apply jpegtran only to proper images by letting bins rotate the
> original image (another config. setting), which should be a "nice"
> size by jpegtran's standards.
That worked perfectly.
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