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In lugnet.cad, Timothy Gould wrote:
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Its just a pity that with 24bit colour everywhere, aliasing is used on
everything (and of course it is hard to reverse). I remember in the good old
days of 256 colour images where aliasing was only for the very, very best
pictures.
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Just as a note, it’s actually antialiasing, not aliasing. Aliasing (aka
jaggies) is the problem that antialiasing solves. And you’re right; it’s very
difficult to undo normally. On the other hand, for images that stickers are
likely to be made for, down-sampling to very few colors will mostly get rid of
the problem, and the pixels can be cleaned up by hand after that.
--Travis
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In lugnet.cad, Travis Cobbs wrote:
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In lugnet.cad, Timothy Gould wrote:
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Its just a pity that with 24bit colour everywhere, aliasing is used on
everything (and of course it is hard to reverse). I remember in the good old
days of 256 colour images where aliasing was only for the very, very best
pictures.
|
Just as a note, it’s actually antialiasing, not aliasing. Aliasing (aka
jaggies) is the problem that antialiasing solves. And you’re right; it’s
very difficult to undo normally. On the other hand, for images that stickers
are likely to be made for, down-sampling to very few colors will mostly get
rid of the problem, and the pixels can be cleaned up by hand after that.
--Travis
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I did know that ;-) (and checked through all documents to make sure I had it
right). I blame it on posting too long after I’d turned into a pumpkin.
The thing is, anti-aliasing should be invertible if you know the routine used to
perform it in the first place. Of course it could be very slow as you have to
invert a #pixels x #pixels matrix (althought it would be sparse). Maybe someone
could write a GIMP or Photoshop plugin for it.
Tim
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In lugnet.cad, Timothy Gould wrote:
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The thing is, anti-aliasing should be invertible if you know the routine
used to perform it in the first place.
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Hmm, I don’t think so. Traditional antialiasing spreads the partial
pixel errors from a line (or edge) into the adjacent pixels. In order
to undo it you’d need to know where the line is, but that’s the very
information you’re trying to recover from the image.
In this case you’re not working from an antialiased image, but rather
one that has been sampled by a scanner or a digital camera. There was
no antialiasing applied. They just save what they see, blended colors
and all.
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Maybe someone could write a GIMP or Photoshop plugin for it.
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I’m pretty certain they already have edge sharpening and unblur
convolution filters which should be useful for undoing some of the
blending, before converting to the closest ldraw colors.
Have fun,
Don
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Hmm, I don’t think so. Traditional antialiasing spreads the partial
pixel errors from a line (or edge) into the adjacent pixels. In order
to undo it you’d need to know where the line is, but that’s the very
information you’re trying to recover from the image.
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Strictly speaking though, (almost) any filter is invertible. Of course you do
need to know what the original filter was which is easier said than done.
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In this case you’re not working from an antialiased image, but rather
one that has been sampled by a scanner or a digital camera. There was
no antialiasing applied. They just save what they see, blended colors
and all.
|
Although it even worse as the image has been stored a a jpeg which bleeds the
colours even more in its compression algorithm.
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I’m pretty certain they already have edge sharpening and unblur
convolution filters which should be useful for undoing some of the
blending, before converting to the closest ldraw colors.
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Yes but edge sharpening actually seems to make the antialiasing worse. If it
finds an ‘edge’ between the ‘real’ colour and its fake neighbour it tries to
exaggerate this. I suspect it has something to do with the frequency offsets in
Fourier space.
Will do,
Tim
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In lugnet.cad, Timothy Gould wrote:
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Hmm, I don’t think so. Traditional antialiasing spreads the partial
pixel errors from a line (or edge) into the adjacent pixels. In order
to undo it you’d need to know where the line is, but that’s the very
information you’re trying to recover from the image.
|
Strictly speaking though, (almost) any filter is invertible. Of course
you do need to know what the original filter was which is easier said
than done.
|
Yeah, but if you think of line antialiasing as a sort of blur filter,
you’ll notice the convolution kernel is directional. The blurring occurs
perpendicular to the direction of the line. This implies a different
filter for each line segment on an edge. Knowing the direction of ALL
the filters is the same as knowing where the lines are.
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In lugnet.cad, Timothy Gould wrote:
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Hmm, I don’t think so. Traditional antialiasing spreads the partial
pixel errors from a line (or edge) into the adjacent pixels. In order
to undo it you’d need to know where the line is, but that’s the very
information you’re trying to recover from the image.
|
Strictly speaking though, (almost) any filter is invertible. Of course you do
need to know what the original filter was which is easier said than done.
|
That may be true, but antialiasing isn’t a filter in that sense. When applied
to computer-generated graphics, it’s calculated during rendering using
information that isn’t available in the final image. When aplied during image
scaling (shrinking), it makes use of the image information in the original
(higher-resolution) image. The antialiasing you see in digital camera images is
a combination of a physical antialiasing filter placed in front of the camera
sensor (often integrated into the camera’s IR filter, apparently) and smoothing
algorithms. So even if you knew which form of antialiasing was used on a
particular image, I don’t think you could create a filter to undo it.
--Travis
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