Re: [Gegl-developer] Proposition : GeglInterpolator
What I tried to do with the gegl_interpolator was in fact what gimp is
doing in gimpdrawable-transform,
Gimp only downsamples in the scale-funcs not during the transformation .
I'm not sure if it is possible to corectly downsample during transformation.
So the resampler should use a transformation matrix, and take source
coördinates.
instead of :
matrix3_copy (inverse, matrix);
matrix3_invert (inverse);
fu = du = inverse[0][0] * dest-x + inverse[0][1] * dest-y + inverse[0][2] -
src-x;
fv = dv = inverse[1][0] * dest-x + inverse[1][1] * dest-y + inverse[1][2] -
src-y;
for (dest_ptr = dest_buf, y = 0; y dest-height; y++)
{
for (x = 0; x dest-width; x++)
{
gegl_interpolator_get (interpolator, fu, fv, dest_buf);
fu += inverse [0][0];
fv += inverse [1][0];
}
du += inverse [0][1];
dv += inverse [1][1];
fu = du;
fv = dv;
...
}
The transformed coordinates should be calculated within the resampler.
gegl_resampler_set_matrix(resampler, matrix);
for (y = 0; y dest-height; y++)
{
for (x = 0; x dest-width; x++)
{
gegl_resampler_get (resampler, x, y, dest_buf);
}
...
}
The gegl_resampler_get should then calculate the number of transformed
coordinates needed by the
resampling method (lanczos/bicubic/bilinear/nearest) as in
gimpdrawable-transform.
ca= cos a
sa = sin a
. = don't touch
gegl_resampler_set_matrix_identity()
| 10 0 |
| 01 0 |
| 00 1 |
gegl_resampler_set_scale(x, y)
| *sy . 0 |
| .*sy 0 |
| .. 1 |
gegl_resampler_set_translscale(tx, ty)
| .. 0 |
| .. 0 |
| tx ty1 |
gegl_resampler_set_rotate(a)
| *ca *sa 0 |
| *-sa *ca 0 |
| .. 1 |
gegl_resampler_set_matrix(a,b,c,d,e,f )
| ad0 |
| be0 |
| cf1 |
Geert
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Re: [Gegl-developer] Proposition : GeglInterpolator
Nope, the point is that interpolation is wrong when scaling down you as will happen when scaling down using an affine transform or a perspective transform. By transforming the corners of a pixel, one would get an idea about the size needed for the resampling kernel. If you scale a image to 10% of the original size using cubic, you have a situation where the data for each destination pixel is taken from a region of 4x4pixel, whilst it should at least be taken from a region of 10x10pixels, 84% of the image data is thrown away. OK, the handling of scaling down is not yet in the proposition Could we not just add the scale factor to the API ? ___ Gegl-developer mailing list Gegl-developer@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gegl-developer
Re: [Gegl-developer] Proposition : GeglInterpolator
On 10/17/06, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote: If you scale a image to 10% of the original size using cubic, you have a situation where the data for each destination pixel is taken from a region of 4x4pixel, whilst it should at least be taken from a region of 10x10pixels, 84% of the image data is thrown away. OK, the handling of scaling down is not yet in the proposition Could we not just add the scale factor to the API ? The scale factor is not enough, if we scale it to 10% horizontally and 70% vertically (or add some kind of rotation as well). A fixed scale factor would no longer be correct. Doing a reverse transform of the corners of the destination pixel would give us all the information we need, and work for perspective transforms as well, hence the method I suggested. /Øyvind K. -- «The future is already here. It's just not very evenly distributed» -- William Gibson http://pippin.gimp.org/http://ffii.org/ ___ Gegl-developer mailing list Gegl-developer@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gegl-developer
Re: [Gegl-developer] Proposition : GeglInterpolator
I've added the implementation to bug report : Bug 360888 – Interpolation
for operations
GeglInterpolator
+ GeglInterpolatorNearest
|
+ GeglInterpolatorLinear
|
+ GeglInterpolatorCubic
|
+ GeglInterpolatorLanczos
usage :
void displacementmap(GeglBuffer *src,
GeglBuffer *aux,
GeglBuffer *dst,
gdouble scale,
gint cx,
gint cy)
{
gint i, j, k;
gint dst_pos;
gdouble dx, dy, xc, yc;
gfloat *buf = g_malloc0 (4 * 4 * 4);
gfloat *aux_buf = g_malloc0 (aux-width * aux-height * 4 * 4);
gfloat *dst_buf = g_malloc0 (dst-width * dst-height * 4 * 4);
gegl_buffer_get_fmt (aux, aux_buf, babl_format (RGBA float));
gegl_buffer_get_fmt (dst, dst_buf, babl_format (RaGaBaA float));
* GeglInterpolatorCubic *interpolator = g_object_new
(GEGL_TYPE_INTERPOLATOR_CUBIC,
input, src,
format, babl_format (RaGaBaA float),
NULL);
gegl_interpolator_prepare(GEGL_INTERPOLATOR(interpolator)) ; *
for (i = 0; i src-height; i++)
for (j = 0; j src-width; j++)
{
/* Calculate x/y - offset relative to origin */
dx = (gdouble) j / (src-width-1.0);
dy = (gdouble) i / (src-height-1.0);
xc = j + (gint) (displacement (aux, aux_buf, dx, dy, cx) * scale);
yc = i + (gint) (displacement (aux, aux_buf, dx, dy, cy) * scale);
* gegl_interpolator_get(GEGL_INTERPOLATOR(interpolator), xc, yc, buf);
/* returns a interpolated pixel in dst */ *
dst_pos = (i * dst-width + j )* 4;
for (k = 0 ; k 4 ; k++)
dst_buf[dst_pos+k]= buf[k];
}
gegl_buffer_set_fmt (dst, dst_buf, babl_format (RaGaBaA float));
g_object_unref (interpolator);
g_free (aux_buf);
g_free (dst_buf);
}
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