System Information

OpenCV 4.12.0-dev

Detailed description

img = cv.imread("033.png",cv.IMREAD_UNCHANGED) successfully read the APNG image but cv.IMREAD_GRAYSCALE and cv.IMREAD_COLOR fails.

Steps to reproduce

using test image https://github.com/onevcat/APNGKit/blob/master/Tests/APNGKitTests/Resources/SpecTesting/033.png

import cv2 as cv

img = cv.imread("033.png",cv.IMREAD_UNCHANGED)
print(cv.imwrite("033_0.png", img))

img = cv.imread("033.png",cv.IMREAD_GRAYSCALE)
if not img is None:
    print(cv.imwrite("033_0.png", img))

img = cv.imread("033.png",cv.IMREAD_COLOR)
if not img is None:
    print(cv.imwrite("033_0.png", img))

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues, forum.opencv.org, Stack Overflow, etc and have not found any solution
• I updated to the latest OpenCV version and the issue is still there
• There is reproducer code and related data files (videos, images, onnx, etc)