引言

最近有需求需要进行如下步骤

  1. 透明背景转白色背景
  2. 白色背景和划痕底图混合模式进行滤色
  3. 白色背景转透明背景

代码

透明背景转白色背景

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def transparent2white(img_path):
    img = Image.open(img_path)
    if img.mode != 'RGBA':
        img = img.convert('RGBA')
    width = img.width
    height = img.height

    # 生成一张白色图片
    new_img = Image.new('RGB', size=(width, height), color=(255, 255, 255))
    new_img.paste(img, (0, 0), mask=img)    # 将原透明图片覆盖到白色图片上
    # pillow为RGB格式，opencv为BGR格式。输出将RGB转为BGR的ndarray格式
    img = cv2.cvtColor(np.asarray(new_img), cv2.COLOR_RGB2BGR)
    return img

混合模式滤色

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def screen(img1, img2):    # 滤色
    """
    img1和img2均为opencv处理图片时的ndarray类型
    """
    img1 = img1 / 255.0
    img2 = img2 / 255.0
    img = 1 - np.multiply((1 - img1), (1 - img2))   # 根据滤色算法矩阵相乘
    img = (img*255).astype(np.uint8)
    img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)  # 输出将BGR转RGB的ndarray格式
    return img

白色背景转透明背景

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def white2transparent(img_ndarray):
    threshold = 100
    dist = 5
    img = Image.fromarray(img_ndarray).convert('RGBA')
    arr = np.array(np.asarray(img))
    r, g, b, a = np.rollaxis(arr, axis=-1)
    mask = ((r>threshold) & (g>threshold) & (b>threshold) & (np.abs(r-g)<dist) & (np.abs(r-b)<dist) & (np.abs(g-b)<dist))
    arr[mask, 3] = 0
    img = Image.fromarray(arr, mode='RGBA')
    return img

整体代码

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import cv2
import numpy as np
from PIL import Image


def transparent2white(img_path):
    img = Image.open(img_path)
    if img.mode != 'RGBA':
        img = img.convert('RGBA')
    width = img.width
    height = img.height

    # 生成一张白色图片
    new_img = Image.new('RGB', size=(width, height), color=(255, 255, 255))
    new_img.paste(img, (0, 0), mask=img)    # 将原透明图片覆盖到白色图片上
    # pillow为RGB格式，opencv为BGR格式。输出将RGB转为BGR的ndarray格式
    img = cv2.cvtColor(np.asarray(new_img), cv2.COLOR_RGB2BGR)
    return img


def screen(img1, img2):    # 滤色
    """
    img1和img2均为opencv处理图片时的ndarray类型
    """
    img1 = img1 / 255.0
    img2 = img2 / 255.0
    img = 1 - np.multiply((1 - img1), (1 - img2))   # 根据滤色算法矩阵相乘
    img = (img*255).astype(np.uint8)
    img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)  # 输出将BGR转RGB的ndarray格式
    return img


def white2transparent(img_ndarray):
    threshold = 100
    dist = 5
    img = Image.fromarray(img_ndarray).convert('RGBA')
    arr = np.array(np.asarray(img))
    r, g, b, a = np.rollaxis(arr, axis=-1)
    mask = ((r>threshold) & (g>threshold) & (b>threshold) & (np.abs(r-g)<dist) & (np.abs(r-b)<dist) & (np.abs(g-b)<dist))
    arr[mask, 3] = 0
    img = Image.fromarray(arr, mode='RGBA')
    return img


white_img = transparent2white('transparent.png')
basemap_img = cv2.imread('basemap.jpg')
colorfilter_img = screen(white_img, basemap_img)
white2transparent(colorfilter_img).save('final.png', format='PNG')