invert y axis and retain image python

Question

I have a custom game engine I am writing, where I feed a sprite sheet into a python file to produce a JSON detailing which of the 8 adjacent spaces can have a given tile layer appear.

I am attempting to create a bounding outline of each sprite in a sprite sheet and I need to be able to translate opencv's imread from an origin of 0,0 being at the top left corner -> bottom left corner as the origin.

I know I can flip the image, but that's not what I'm looking for. I want to invert the y axis such that y increases from the bottom to top, while the x-axis remains unchanged.

Have also seen examples where, using MatPlotLib, the y axis itself can be inverted. But I need to be able to read pixel colors, which is why OpenCV was preferable.

Answer 1

Have you tried re-indexing the image array so that the Y-axis is inverted while the X-axis remains unchanged. In this case, you don't need to flip the image or manipulate the axes using Matplotlib. Instead, you can simply access the pixel values by inverting the Y-coordinate with respect to the image height.

import cv2

def get_inverted_y_pixel(image, x, y):
    inverted_y = image.shape[0] - 1 - y
    return image[inverted_y, x]

def main():
    image_path = 'path/to/your/sprite_sheet.png'
    image = cv2.imread(image_path)

# Accessing a pixel with inverted Y-axis
x, y = 100, 50
pixel_color = get_inverted_y_pixel(image, x, y)

print(f"Pixel color at ({x}, {y}): {pixel_color}")

if __name__ == "__main__":
    main()
#In this example, the get_inverted_y_pixel function inverts the Y-axis 
#for the given coordinates and returns the pixel color from the OpenCV image.