Imshow 不需要从 BGR 转换为 RGB

据我所知，OpenCV 以 BGR 色彩空间的顺序读取图像，我们通常必须像这样把它转换回 RGB:

img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)

但是当我试图简单地阅读一张图片并展示它时，颜色看起来很好(不需要将 BGR 转换成 RGB) :

img_bgr = cv2.imread(image_path)
cv2.imshow('BGR Image',img_bgr)
img_rgb = cv2.cvtColor(img_bgr, cv2.COLOR_BGR2RGB)
cv2.imshow('RGB Image',img_rgb )
cv2.waitkey(0)

那么 imshow()是自动改变函数内的顺序(从 BGR 到 RGB)还是一直都是 BGR？

156239 次浏览
小开
最佳答案

BGR and RGB are not color spaces, they are just conventions for the order of the different color channels. cv2.cvtColor(img, cv2.COLOR_BGR2RGB) doesn't do any computations (like a conversion to say HSV would), it just switches around the order. Any ordering would be valid - in reality, the three values (red, green and blue) are stacked to form one pixel. You can arrange them any way you like, as long as you tell the display what order you gave it.

OpenCV imread, imwrite and imshow indeed all work with the BGR order, so there is no need to change the order when you read an image with cv2.imread and then want to show it with cv2.imshow.

While BGR is used consistently throughout OpenCV, most other image processing libraries use the RGB ordering. If you want to use matplotlib's imshow but read the image with OpenCV, you would need to convert from BGR to RGB.

小开 
screen = cv2.cvtColor(screen, cv2.COLOR_RGB2BGR)

this one line code changes rgb to bgr

小开

If you do not need to use any other Image processing library (example Matplotlib's imshow), there is no need to do color scale conversion. Below code is an example, where the color scale conversion is done but when the image is loaded, it is still loaded in BGR. This conversion is not needed as the image is displayed using cv2.imshow().

import cv2


# read the image #
image = cv2.imread('<<Image Path>>')
                

image_rgb = cv2.cvtColor(image,cv2.COLOR_BGR2RGB)


# write a function to draw circles on the image #
def draw_circle(event,x,y,flags,params):
if event == cv2.EVENT_RBUTTONDOWN:
cv2.circle(img=image_rgb,center=(x,y),radius=100,color=(0,0,255),thickness=10)


# Open CV callbacks #
cv2.namedWindow(winname='ImageWindow')
cv2.setMouseCallback('ImageWindow',draw_circle)


# display the image till the user hits the ESC key #
while True:
cv2.imshow('ImageWindow',image_rgb)
if cv2.waitKey(20) & 0xFF == 27:
break
        

cv2.destroyAllWindows()
小开

Alternatively, you can use imutils.opencv2matplotlib() function, which does not need BGR to RGB conversion.

小开 
opencv_image_with_bgr_channels = cv2.imread('path/to/color_image.jpg')


matplotlib_compatible_image_with_rgb_channels = opencv_image_with_bgr_channels[:,:, ::-1]

This converts BGR to RGB Channels Image by reversing the channels.

小开

for matplotlib we need to change BGR to RGB:

img = cv2.imread("image_name")
img = img[...,::-1]


plt.imshow(img)

提交答案