使用 python Wand 替换颜色但坐标未知

Question

I am aware of Replace a color using Wand and Change color of specific pixels [Wand] but both of these use a line like

    draw.color(192,84,'replace')

In which you need to pass the location of a pixel of the relevant color. What if you know the color you want to replace but not its location? I want to replace the color of pixels in an image without passing a reference to the location of a pixel of that color. Do you really have to scan the entire image looking for something you already know is there?

The imagemagick equivalent would be

convert balloon.gif -fill white -opaque blue balloon_white.gif

Answer 1

If you want to match -opaque functionality, then you'll need to implement the MagickOpaquePaintImage C method.

import ctypes
from wand.api import library
from wand.image import Image
from wand.color import Color
from wand.compat import nested

# Map C-API to Python
library.MagickOpaquePaintImage.argtypes = (ctypes.c_void_p,  # Wand
                                           ctypes.c_void_p,  # target
                                           ctypes.c_void_p,  # fill
                                           ctypes.c_double,  # fuzz
                                           ctypes.c_bool)    # invert

with Image(filename='rose:') as img:
    with nested(Color('#E93A43'), Color('ORANGE')) as (target, fill):
        library.MagickOpaquePaintImage(img.wand,
                                       target.resource,
                                       fill.resource,
                                       img.quantum_range * 0.10, # -fuzz 10%
                                       False)
    img.save(filename='output.png')

Answer 2

Since wand 0.5.4 the method opaque_paint is available so the clever hack @emcconville proposed is not required anymore. You can do just:

from wand.image import Image
with Image(filename='rose:') as im:
  im.opaque_paint(target='#E93A43', fill='Orange', fuzz=0.10)
  im.save(filename='output.png')