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by NicolasRobidoux
2010-11-12T20:41:43-07:00
Forum: Developers
Topic: image size convention in resize.c
Replies: 37
Views: 78578

Re: image size convention in resize.c

The resizes which don't involve the resample code (a.k.a. distort) methods simply only give weights to the points within the support which actually are within the image (this is not equivalent to using the nearest neighbour a.k.a. smear abyss policy). This is like chopping off the piece of the kerne...
by NicolasRobidoux
2010-11-12T18:50:21-07:00
Forum: Developers
Topic: image size convention in resize.c
Replies: 37
Views: 78578

Re: image size convention in resize.c

Nicholas, Not sure I follow all this, but it looks like how the filter kernel is extended at the edges of the image or more precisely how the image is extended so that a full kernel can be use. I am not absolutely sure -resize works with -virtual-pixel, but -virtual-pixel allows one to extend the i...
by NicolasRobidoux
2010-11-12T08:32:53-07:00
Forum: Developers
Topic: image size convention in resize.c
Replies: 37
Views: 78578

Re: image size convention in resize.c

I'll get going on this slowly. There are, actually, three desirable behaviors: corners (current behavior, and default; it extrapolates when upsampling) centers (it extrapolates when downsampling) and switch (mix and match depending on whether one is enlarging or downsampling in each direction; it ne...
by NicolasRobidoux
2010-11-11T14:28:54-07:00
Forum: Developers
Topic: image size convention in resize.c
Replies: 37
Views: 78578

Re: image size convention in resize.c

Things are a bit different for man-made images, because generally they are made with a priori awareness of the total extent of the image. For such (the dragon picture, say) I could understand one preferring the current IM default (match corners) even when enlarging, because it is better at preservin...
by NicolasRobidoux
2010-11-11T13:47:22-07:00
Forum: Developers
Topic: image size convention in resize.c
Replies: 37
Views: 78578

Re: image size convention in resize.c

Here are some examples of the difference between the two image size conventions (done with my first private pass at changing the code): The 8x enlargement of the IM built-in rose picture: convert rose: -resize 560x560 rose_corners.png resulted in http://web.cs.laurentian.ca/nrobidoux/misc/rose_corne...
by NicolasRobidoux
2010-11-09T14:21:54-07:00
Forum: Developers
Topic: image size convention in resize.c
Replies: 37
Views: 78578

Re: image size convention in resize.c

Note however that the difference jumps at you when enlarging a small image.
by NicolasRobidoux
2010-11-09T14:18:38-07:00
Forum: Developers
Topic: image size convention in resize.c
Replies: 37
Views: 78578

Re: image size convention in resize.c

1) Personal/professional: To do careful quantitative comparative testing of resampling methods, it is preferable to be able to switch image size convention (because some methods are more "friendly" to one or another of the conventions, and this levels the field; there is another reason, having to do...
by NicolasRobidoux
2010-11-08T09:43:27-07:00
Forum: Developers
Topic: image size convention in resize.c
Replies: 37
Views: 78578

Re: image size convention in resize.c

I'm going to take my time on this: I'm realizing now that to do this just right, I need to be extremely careful. It's not only the sampling positions that need to be changed, but also the way the filter kernel is scaled depending on the "resize factors." And there are other things to double check (c...
by NicolasRobidoux
2010-11-07T08:57:33-07:00
Forum: Developers
Topic: image size convention in resize.c
Replies: 37
Views: 78578

Re: image size convention in resize.c

I'll wait until I have a substantial quiet block of time to make changes. The "new" IM resize is more complex than the old version on which I did this switch years ago.
by NicolasRobidoux
2010-11-05T17:32:47-07:00
Forum: Developers
Topic: image size convention in resize.c
Replies: 37
Views: 78578

Re: image size convention in resize.c

Opinions: A switch would be nice. The default should be: For resize, switch depending on what is done in each direction (so, when enlarging in one direction and reducing in the other, both conventions would be used, depending on the direction). For everything else, "match corners" (the current defau...
by NicolasRobidoux
2010-11-05T13:46:37-07:00
Forum: Developers
Topic: image size convention in resize.c
Replies: 37
Views: 78578

image size convention in resize.c

Notation: When resizing, the sampled (input) image has m rows and n columns, the output image has M rows and N columns, output pixels are indexed with (I,J) with 0<=I<=M-1 and 0<=J<=N-1, and coordinates are set so that they equal the index right at a pixel location. (x,y) is a position in the "input...
by NicolasRobidoux
2010-09-28T06:18:35-07:00
Forum: Developers
Topic: Second even bigger improvement for Distorts [CLOSED]
Replies: 6
Views: 18540

Re: Second even bigger improvement for Distorts

Chantal Racette would like to point out that she is "only" a Masters student.
by NicolasRobidoux
2010-09-25T16:41:51-07:00
Forum: Developers
Topic: what is up with svn?
Replies: 29
Views: 50643

Re: what is up with svn?

It appears that ohloh stopped understanding the svn link for imagemagick in February or so. Maybe changing the download server link to the one used by Anthony would fix that? (It's not a great tragedy if ohloh does not update, but it's nice if it does.) Cristy is the ohloh imagemagick manager.
by NicolasRobidoux
2010-09-20T11:13:14-07:00
Forum: Developers
Topic: what is up with svn?
Replies: 29
Views: 50643

Re: what is up with svn?

anthony wrote:I have been using
svn co https://magick.imagemagick.org/subversi ... gick/trunk .
for years to get the development tree.
Well, well, well.

This works without chenanigans \o/
by NicolasRobidoux
2010-09-20T05:01:19-07:00
Forum: Developers
Topic: Cheaper sinc computation for resize.c
Replies: 83
Views: 144795

Re: Cheaper sinc computation for resize.c

LanczosFast is gone as of version 2684. Update to SVN version 2685... Removed LanczosFast from filter types and command line option parsing "resample.h" and "option.c" respecivally Added comment in ChangeLog for svn 2686 Apologies (I know better): I forgot to do a "find" on every occurence of Lancz...