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OpenCV Color Conversion Discrepancy in Image Loading
When attempting to load and display a color image using Python OpenCV, users may encounter unexpected color deviations in the resulting image. This issue arises due to a difference in the default color ordering schemes between OpenCV and the Matplotlib library.
Problem Description
The code provided by the user involves loading a color image using OpenCV's cv2.imread() function and converting it to grayscale using cv2.cvtColor(). Subsequently, both the original image and the grayscale image are plotted using Matplotlib's plt.imshow() function. Despite using the IMREAD_COLOR flag, the plotted image exhibits distorted colors.
Underlying Issue
By default, OpenCV utilizes the Blue-Green-Red (BGR) color ordering for images, while Matplotlib uses Red-Green-Blue (RGB). When the image loaded by OpenCV is displayed in Matplotlib, the channels are inverted, leading to the color discrepancy.
Solution
To resolve this issue, the user can explicitly convert the BGR image loaded from OpenCV to RGB using the cv2.cvtColor() function. The converted RGB image can then be used for plotting in Matplotlib.
<code class="python">import cv2 import matplotlib.pyplot as plt # Load image in BGR img = cv2.imread('lena_caption.png', cv2.IMREAD_COLOR) # Convert BGR to RGB RGB_img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB) # Plot RGB image in Matplotlib plt.imshow(RGB_img) plt.title('Original Image in RGB') plt.xticks([]), plt.yticks([]) plt.show()</code>
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