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app: fix gradient dithering

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In gimp:gradient, fix dithering to correspond to how we actually
round float values to 8-bit.  In particular, this avoids
introducing noise when a component is fixed at 0 or 1 along a
segment.
This commit is contained in:
Ell 2019-07-19 21:38:18 +03:00
parent 60554eaed9
commit e22fcc8942
1 changed files with 33 additions and 30 deletions
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63
app/operations/gimpoperationgradient.c
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@ -158,6 +158,10 @@ static void gradient_put_pixel (gint
GimpRGB *color,
gpointer put_pixel_data);
static void gradient_dither_pixel (GimpRGB *color,
GRand *dither_rand,
gfloat *dest);
static gboolean gimp_operation_gradient_process (GeglOperation *operation,
GeglBuffer *input,
GeglBuffer *output,
@ -985,22 +989,9 @@ gradient_put_pixel (gint x,
if (ppd->dither_rand)
{
gfloat r, g, b, a;
gint i = g_rand_int (ppd->dither_rand);
gradient_dither_pixel (color, ppd->dither_rand, dest);
r = color->r + (gdouble) (i & 0xff) / 256.0 / 256.0; i >>= 8;
g = color->g + (gdouble) (i & 0xff) / 256.0 / 256.0; i >>= 8;
b = color->b + (gdouble) (i & 0xff) / 256.0 / 256.0; i >>= 8;
if (color->a > 0.0 && color->a < 1.0)
a = color->a + (gdouble) (i & 0xff) / 256.0 / 256.0;
else
a = color->a;
*dest++ = MAX (r, 0.0);
*dest++ = MAX (g, 0.0);
*dest++ = MAX (b, 0.0);
*dest++ = MAX (a, 0.0);
dest += 4;
}
else
{
@ -1011,6 +1002,31 @@ gradient_put_pixel (gint x,
}
}
static void
gradient_dither_pixel (GimpRGB *color,
GRand *dither_rand,
gfloat *dest)
{
gfloat r, g, b, a;
guint i;
i = g_rand_int (dither_rand);
r = color->r + (gdouble) (i & 0xff) / 256.0 / 256.0 - 0.5 / 256.0; i >>= 8;
g = color->g + (gdouble) (i & 0xff) / 256.0 / 256.0 - 0.5 / 256.0; i >>= 8;
b = color->b + (gdouble) (i & 0xff) / 256.0 / 256.0 - 0.5 / 256.0; i >>= 8;
if (color->a > 0.0 && color->a < 1.0)
a = color->a + (gdouble) (i & 0xff) / 256.0 / 256.0 - 0.5 / 256.0;
else
a = color->a;
*dest++ = CLAMP (r, 0.0, 1.0);
*dest++ = CLAMP (g, 0.0, 1.0);
*dest++ = CLAMP (b, 0.0, 1.0);
*dest++ = CLAMP (a, 0.0, 1.0);
}
static gboolean
gimp_operation_gradient_process (GeglOperation *operation,
GeglBuffer *input,
@ -1138,24 +1154,11 @@ gimp_operation_gradient_process (GeglOperation *operation,
for (x = roi->x; x < endx; x++)
{
GimpRGB color = { 0.0, 0.0, 0.0, 1.0 };
gfloat r, g, b, a;
gint i = g_rand_int (dither_rand);
gradient_render_pixel (x, y, &color, &rbd);
gradient_dither_pixel (&color, dither_rand, dest);
r = color.r + (gdouble) (i & 0xff) / 256.0 / 256.0; i >>= 8;
g = color.g + (gdouble) (i & 0xff) / 256.0 / 256.0; i >>= 8;
b = color.b + (gdouble) (i & 0xff) / 256.0 / 256.0; i >>= 8;
if (color.a > 0.0 && color.a < 1.0)
a = color.a + (gdouble) (i & 0xff) / 256.0 / 256.0;
else
a = color.a;
*dest++ = MAX (r, 0.0);
*dest++ = MAX (g, 0.0);
*dest++ = MAX (b, 0.0);
*dest++ = MAX (a, 0.0);
dest += 4;
}
}
else