[cairo] antialias for images?

[Peter Goetz]

As you already supposed I started with a high resolution source image.
I also change the order of rotation and scale. With no success.
Even if I don't rotate at all and just scale the image down, I get a
non-antialiased result.

Any suggestions? Thanks again for help!


2007/10/15, Thomas Stover <thomas at wsinnovations.com>:
>
> > Date: Mon, 15 Oct 2007 01:24:35 +0200
> > From: "Peter Goetz" <peter.gtz2 at gmail.com>
> > Subject: [cairo] antialias for images?
> > To: cairo at cairographics.org
> > Message-ID:
> >       <64acc4780710141624ye4eadcbq4d6a91999c86ca5c at mail.gmail.com>
> > Content-Type: text/plain; charset="iso-8859-1"
> >
> > Hi all,
> > I'm trying to scale and rotate an image and then put it on a surface
> > using paint as it is shown in one of the examples.
> > However the scaling is not done by something like a bicubic filter but
> > just by a linear one, so the picture looks very noisy (see screenshot
> > attached) and has a staircase effect on the edges.
> > Is there a way to make it look smooth? Some antialias for images? I
> > haven't found something in the mail-archives.
> > Thanks for your help!
> > Peter
> >
> > Source-code:
> >
> > #include <cairo.h>
> >
> > int main (int argc, char *argv[])
> > {
> >        cairo_surface_t *surface;
> >        cairo_t *cr;
> >        int w, h;
> >        cairo_surface_t *image;
> >
> >        surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, 256, 256);
> >        cr = cairo_create (surface);
> >
> >        double M_PI=3.14;
> >
> >        image = cairo_image_surface_create_from_png ("test.png");
> >        w = cairo_image_surface_get_width (image);
> >        h = cairo_image_surface_get_height (image);
> >
> >        cairo_translate (cr, 128.0, 128.0);
> >        cairo_rotate (cr, 20* M_PI/180);
> >        cairo_scale  (cr, 256.0/w, 256.0/h);
> >        cairo_translate (cr, -0.5*w, -0.5*h);
> >
> >        cairo_set_source_surface (cr, image, 0, 0);
> >        cairo_paint (cr);
> >
> >        cairo_surface_destroy (image);
> >
> >        cairo_destroy (cr);
> >        cairo_surface_write_to_png (surface, "output.png");
> >        cairo_surface_destroy (surface);
> >
> >        return 0;
> > }
> > -------------- next part --------------
> > A non-text attachment was scrubbed...
> > Name: output.png
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> > Desc: not available
> > Url : http://lists.cairographics.org/archives/cairo/attachments/20071015/cb14c4d6/attachment.png
>
> Note: I'm new to cairo myself, and this answer is based on nothing but
> intuition.
>
> I think if the source image "test.png" is low-res then there is not much
> that can be done. However, if you start out with a higher resolution
> source image (maybe you are already), then do your rotation and effects
> at a high resolution inside cairo, then as the very last step scale the
> end result down to the smaller size you want - it might look better. In
> other words, first try doing the rotation on a 600x600 file on say a
> 1000x100 cairo surface with no other translate or scales, and just see
> what it looks like. If that looks better, then I think it's a matter of
> finding the right sequence of scale/rotate/translate/matrix operations
> that cairo likes to do everything at high res except for the final scale
> down to 256x256.
>
> This sounds like something I would want to do myself, let us know what
> happens.
>
>
>
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