Cropping tool: fix occasional black borders in export at right/bottom

The image parts from all tiles/blocks are placed on the target canvas by
the cropping tool. The locations of each image parts were slightly off,
because the respective min/max locations in each tile was computed not
as zero-based index but as one-based index. Additionally, the
destination location of each part in the target canvas was accidentally
computed wrongly, because it targeted the last pixel of the previous
part as start of the new part, rather than targeting the next pixel to
avoid an overlap. Both is fixed now.

Author: tomka

CHANGELOG.md

@@ -215,6 +215,10 @@ Miscellaneous:
 - Clicking the Home link in the upper left corner with a project open, will now
   also ask for confirmation (like clicking any data view entry in the menu).
 
+- Cropping tool: in some exported sub volumes a black border of one or two
+  pixels could appear on the right side and the bottom. This is fixed now and
+  the entire space of the exported image is used correctly.
+
 ## Maintenance updates
 
 - Node distance measurements: computation of straight line distance has been

django/applications/catmaid/control/cropping.py

@@ -490,23 +490,27 @@ def extract_substack_no_rotation(job) -> List:
             image_parts = []
             x_dst = bb.px_x_offset
             for nx, x in enumerate( range(tile_x_min, tile_x_max + 1) ):
-                # The min x,y for the image part in the current tile are 0
-                # for all tiles except the first one.
-                cur_px_x_min = 0 if nx > 0 else bb.px_x_min - x * tile_width
-                # The max x,y for the image part of current tile are the tile
-                # size minus one except for the last one.
+                # The min x,y index for the image part in the current tile are 0
+                # for all tiles except the first one, where we can start within
+                # a tile. In that case we also have to subtract one to make it
+                # an index value (starting at 0).
+                cur_px_x_min = 0 if nx > 0 else bb.px_x_min - x * tile_width - 1
+                # The max x,y index for the image part of current tile are the
+                # tile size minus one except for the last one. For instance, a
+                # 64x63 tile will have a max x index of 63 (again, starting at 0).
                 if nx < (num_x_tiles - 1):
                     cur_px_x_max = tile_width - 1
                 else:
-                    cur_px_x_max = bb.px_x_max - x * tile_width
+                    cur_px_x_max = bb.px_x_max - x * tile_width - 1
                 # Reset y destination component
                 y_dst = bb.px_y_offset
                 for ny, y in enumerate( range(tile_y_min, tile_y_max + 1) ):
-                    cur_px_y_min = 0 if ny > 0 else bb.px_y_min - y * tile_height
+                    # Similar to cur_px_x_min above
+                    cur_px_y_min = 0 if ny > 0 else bb.px_y_min - y * tile_height - 1
                     if ny < (num_y_tiles - 1):
                         cur_px_y_max = tile_height - 1
                     else:
-                        cur_px_y_max = bb.px_y_max - y * tile_height
+                        cur_px_y_max = bb.px_y_max - y * tile_height - 1
                     # Create an image part definition
                     z = bb.px_z_min + nz
                     source_meta = job.get_source_metadata(stack, mirror, (x, y, z))
@@ -517,10 +521,14 @@ def extract_substack_no_rotation(job) -> List:
                     except Exception as e:
                         # ignore failed slices
                         logger.error(f'An error happend while creating an impagepart: {e}')
-                    # Update y component of destination position
-                    y_dst += cur_px_y_max - cur_px_y_min
-                # Update x component of destination position
-                x_dst += cur_px_x_max - cur_px_x_min
+                    # Update y component of destination position. The next image
+                    # part should not begin with the max location of the current
+                    # part. Therefore, add one to the difference of min/max in
+                    # the current part.
+                    y_dst += cur_px_y_max - cur_px_y_min + 1
+                # Update x component of destination position. The same applies
+                # here as it does for y_dst above.
+                x_dst += cur_px_x_max - cur_px_x_min + 1
 
             # Write out the image parts and make sure the maximum allowed file
             # size isn't exceeded.