使用OpenCV在Python中将RGB图像转换为RGBA的最佳方法是什么?
假设我有一个形状为
(185, 198, 3) - it is RGB
如何将它们合并并保存到文件中?其中一个是形状为(185, 198)
的阿尔法掩码。
使用opencv3,这应该可以工作:
Python
# First create the image with alpha channel
rgba = cv2.cvtColor(rgb_data, cv2.COLOR_RGB2RGBA)
# Then assign the mask to the last channel of the image
rgba[:, :, 3] = alpha_data
C++
# First create the image with alpha channel
cv::cvtColor(rgb_data, rgba , cv::COLOR_RGB2RGBA);
# Split the image for access to alpha channel
std::vector<cv::Mat>channels(4);
cv::split(rgba, channels);
# Assign the mask to the last channel of the image
channels[3] = alpha_data;
# Finally concat channels for rgba image
cv::merge(channels, 4, rgba);
cv2.merge()
将 alpha 通道添加到给定的 RGB 图像中,但首先您需要根据 文档 将 RGB 图像拆分为 R、G 和 B
通道:
这可以通过以下方式完成:Python: cv2.merge(mv[, dst])
- mv – 要合并的输入数组或矩阵向量; mv 中的所有矩阵必须具有相同的大小和深度。
b_channel, g_channel, r_channel = cv2.split(img)
alpha_channel = np.ones(b_channel.shape, dtype=b_channel.dtype) * 50 #creating a dummy alpha channel image.
img_BGRA = cv2.merge((b_channel, g_channel, r_channel, alpha_channel))
alpha_channel = alpha_channel.astype(np.uint8)
,即确保所有通道具有相同的数据类型。 - Minh Triet由于OpenCV图像只是Numpy数组,因此您可以使用一行代码完成此操作,使用Numpy快速高效。因此,这里是设置代码:
import numpy as np
# We'll synthesise a random image and a separate alpha channel full of 128 - semitransparent
im = np.random.randint(0,256,(480,640,3), dtype=np.uint8)
alpha = np.full((480,640), 128, dtype=np.uint8)
这里的解决方案是将alpha通道堆叠到图像的"depth"轴上,使用dstack()
函数实现:
result = np.dstack((im, alpha))
这是另一个使用Grabcut的简单示例,它有助于在将图像保存到磁盘与pyplot
时获取正确的通道顺序。
from matplotlib import pyplot as plt
import numpy as np
import cv2
img = cv2.imread('image.jpg')
mask = np.zeros(img.shape[:2], np.uint8)
bgdModel = np.zeros((1,65), np.float64)
fgdModel = np.zeros((1,65), np.float64)
rect = (50, 50, 450, 290)
# Grabcut
cv2.grabCut(img, mask, rect, bgdModel, fgdModel, 5, cv2.GC_INIT_WITH_RECT)
r_channel, g_channel, b_channel = cv2.split(img)
a_channel = np.where((mask==2)|(mask==0), 0, 255).astype('uint8')
img_RGBA = cv2.merge((r_channel, g_channel, b_channel, a_channel))
cv2.imwrite("test.png", img_RGBA)
# Now for plot correct colors :
img_BGRA = cv2.merge((b_channel, g_channel, r_channel, a_channel))
plt.imshow(img_BGRA), plt.colorbar(),plt.show()
import cv2
import numpy as np
import skimage.exposure
path_input_image="./input_image.png"
input_image = cv2.imread(path_input_image2, cv2.IMREAD_UNCHANGED)
input_image_alphachann = np.full((input_image.shape[0],input_image.shape[1]), 128, dtype=np.uint8)
output_image = np.dstack((input_image, input_image_alphachann))
print(input_image.shape)
print(output_image.shape)
#(400, 200, 3); 3 channell rgb
#(400, 200, 4); 4c channel rgba
print(input_image.dtype)
print(output_image.dtype)
# uint8
path_output_image=path_input_image+'.alpha.png'
cv2.imwrite(path_output_image, output_image)
我将在此发布我的C++答案,因为它可能对其他人有所帮助(已经有足够的Python答案):
std::vector<cv::Mat> matChannels;
cv::split(mat, matChannels);
// create alpha channel
cv::Mat alpha(...);
matChannels.push_back(alpha);
cv::merge(matChannels, dst);