Merge pull request matplotlib#545 from mdboom/alpha_image_resize_bug

Broken alpha handling in images

Author: mdboom

lib/matplotlib/backends/backend_svg.py

@@ -757,6 +757,10 @@ def draw_image(self, gc, x, y, im, dx=None, dy=None, transform=None):
             im.flipud_out()
             attrib['xlink:href'] = filename
 
+        alpha = gc.get_alpha()
+        if alpha != 1.0:
+            attrib['opacity'] = str(alpha)
+
         if transform is None:
             self.writer.element(
                 'image',

lib/matplotlib/image.py

@@ -199,7 +199,7 @@ def _get_unsampled_image(self, A, image_extents, viewlim):
                 im.is_grayscale = False
             else:
                 if self._rgbacache is None:
-                    x = self.to_rgba(self._A, self._alpha, bytes=True)
+                    x = self.to_rgba(self._A, bytes=True)
                     self._rgbacache = x
                 else:
                     x = self._rgbacache
@@ -345,6 +345,7 @@ def draw(self, renderer, *args, **kwargs):
         gc = renderer.new_gc()
         gc.set_clip_rectangle(self.axes.bbox.frozen())
         gc.set_clip_path(self.get_clip_path())
+        gc.set_alpha(self.get_alpha())
 
         if self._check_unsampled_image(renderer):
             self._draw_unsampled_image(renderer, gc)
@@ -722,7 +723,7 @@ def set_data(self, x, y, A):
             A.shape = A.shape[0:2]
         if len(A.shape) == 2:
             if A.dtype != np.uint8:
-                A = self.to_rgba(A, alpha=self._alpha, bytes=True)
+                A = self.to_rgba(A, bytes=True)
                 self.is_grayscale = self.cmap.is_gray()
             else:
                 A = np.repeat(A[:,:,np.newaxis], 4, 2)
@@ -824,7 +825,7 @@ def make_image(self, magnification=1.0):
         width = width * magnification
         height = height * magnification
         if self._rgbacache is None:
-            A = self.to_rgba(self._A, alpha=self._alpha, bytes=True)
+            A = self.to_rgba(self._A, bytes=True)
             self._rgbacache = A
             if self._A.ndim == 2:
                 self.is_grayscale = self.cmap.is_gray()
@@ -851,6 +852,7 @@ def draw(self, renderer, *args, **kwargs):
         gc = renderer.new_gc()
         gc.set_clip_rectangle(self.axes.bbox.frozen())
         gc.set_clip_path(self.get_clip_path())
+        gc.set_alpha(self.get_alpha())
         renderer.draw_image(gc,
                             round(self.axes.bbox.xmin),
                             round(self.axes.bbox.ymin),
@@ -974,7 +976,7 @@ def make_image(self, magnification=1.0):
         if self._A is None:
             raise RuntimeError('You must first set the image array')
 
-        x = self.to_rgba(self._A, self._alpha, bytes=True)
+        x = self.to_rgba(self._A, bytes=True)
         self.magnification = magnification
         # if magnification is not one, we need to resize
         ismag = magnification!=1
@@ -1008,6 +1010,7 @@ def draw(self, renderer, *args, **kwargs):
         gc = renderer.new_gc()
         gc.set_clip_rectangle(self.figure.bbox)
         gc.set_clip_path(self.get_clip_path())
+        gc.set_alpha(self.get_alpha())
         renderer.draw_image(gc, round(self.ox), round(self.oy), im)
         gc.restore()
 
@@ -1096,7 +1099,7 @@ def make_image(self, renderer, magnification=1.0):
                 im.is_grayscale = False
             else:
                 if self._rgbacache is None:
-                    x = self.to_rgba(self._A, self._alpha, bytes=True)
+                    x = self.to_rgba(self._A, bytes=True)
                     self._rgbacache = x
                 else:
                     x = self._rgbacache
@@ -1148,6 +1151,7 @@ def draw(self, renderer, *args, **kwargs):
         l, b, r, t = self.get_window_extent(renderer).extents
         gc = renderer.new_gc()
         self._set_gc_clip(gc)
+        gc.set_alpha(self.get_alpha())
         #gc.set_clip_path(self.get_clip_path())
         renderer.draw_image(gc, round(l), round(b), im)
         gc.restore()

src/_backend_agg.cpp

@@ -988,6 +988,7 @@ RendererAgg::draw_image(const Py::Tuple& args)
     agg::trans_affine affine_trans;
     bool has_affine = false;
     double x, y, w, h;
+    double alpha;
 
     if (args.size() == 7)
     {
@@ -1006,6 +1007,8 @@ RendererAgg::draw_image(const Py::Tuple& args)
                   warnings from the compiler */
     }
 
+    alpha = gc.alpha;
+
     theRasterizer.reset_clipping();
     rendererBase.reset_clipping(true);
     set_clipbox(gc.cliprect, theRasterizer);
@@ -1097,7 +1100,8 @@ RendererAgg::draw_image(const Py::Tuple& args)
     else
     {
         set_clipbox(gc.cliprect, rendererBase);
-        rendererBase.blend_from(pixf, 0, (int)x, (int)(height - (y + image->rowsOut)));
+        rendererBase.blend_from(
+            pixf, 0, (int)x, (int)(height - (y + image->rowsOut)), alpha * 255);
     }
 
     rendererBase.reset_clipping(true);

src/_image.cpp

@@ -33,7 +33,7 @@
 #include "mplutils.h"
 
 
-typedef agg::pixfmt_rgba32 pixfmt;
+typedef agg::pixfmt_rgba32_pre pixfmt;
 typedef agg::renderer_base<pixfmt> renderer_base;
 typedef agg::span_interpolator_linear<> interpolator_type;
 typedef agg::rasterizer_scanline_aa<agg::rasterizer_sl_clip_dbl> rasterizer;