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Merge pull request #29643 from uwezkhan/apng-dispose-elem-size

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fix apng background dispose overrun in png readData
This commit is contained in:
Abhishek Gola
2026-08-04 09:56:19 +05:30
committed by GitHub
parent 6e82dddfb5 6ad702680e
commit 4bee6895eb
2 changed files with 54 additions and 1 deletions
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5
modules/imgcodecs/src/grfmt_png.cpp
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@@ -490,8 +490,11 @@ bool PngDecoder::readData( Mat& img )
{
memcpy(frameNext.getPixels(), frameCur.getPixels(), imagesize);
if (dop == 1)
{
const size_t elem_size = mat_cur.elemSize();
for (j = 0; j < h0; j++)
memset(frameNext.getRows()[y0 + j] + x0 * img.channels(), 0, w0 * img.channels());
memset(frameNext.getRows()[y0 + j] + x0 * elem_size, 0, w0 * elem_size);
}
}
}
else

50
modules/imgcodecs/test/test_animation.cpp
View File

@@ -682,6 +682,56 @@ TEST(Imgcodecs_APNG, animation_imread_preview)
EXPECT_EQ(0, cv::norm(animation.still_image, imread_result, cv::NORM_INF));
}
TEST(Imgcodecs_APNG, decode_dispose_background_gray)
{
Animation animation;
Mat frame(8, 64, CV_8UC1, Scalar(192));
frame(Rect(0, 0, 32, 8)).setTo(Scalar(64));
animation.frames.push_back(frame.clone());
animation.durations.push_back(100);
frame.setTo(Scalar(192));
animation.frames.push_back(frame.clone());
animation.durations.push_back(100);
frame.at<uchar>(0, 0) = 255;
animation.frames.push_back(frame.clone());
animation.durations.push_back(100);
std::vector<unsigned char> buf;
ASSERT_TRUE(imencodeanimation(".png", animation, buf));
// Give the second frame APNG_DISPOSE_OP_BACKGROUND, which the encoder does not
// pick for these frames. dispose_op is the 25th byte of the fcTL payload.
int fcTL_count = 0;
for (size_t i = 8; i + 12 <= buf.size(); )
{
const size_t len = ((size_t)buf[i] << 24) | ((size_t)buf[i + 1] << 16) |
((size_t)buf[i + 2] << 8) | (size_t)buf[i + 3];
if (buf[i + 4] == 'f' && buf[i + 5] == 'c' && buf[i + 6] == 'T' && buf[i + 7] == 'L')
{
if (fcTL_count == 1)
buf[i + 8 + 24] = 1;
fcTL_count++;
}
i += len + 12;
}
ASSERT_EQ(3, fcTL_count);
// The disposed region is the one named by fcTL, whatever the caller asked the
// decoder to convert the frames to.
std::vector<Mat> gray, color;
ASSERT_TRUE(imdecodemulti(buf, IMREAD_UNCHANGED, gray));
ASSERT_TRUE(imdecodemulti(buf, IMREAD_COLOR, color));
ASSERT_EQ(animation.frames.size(), gray.size());
ASSERT_EQ(gray.size(), color.size());
for (size_t i = 0; i < gray.size(); i++)
{
Mat expected;
cvtColor(gray[i], expected, COLOR_GRAY2BGR);
EXPECT_EQ(0, cvtest::norm(expected, color[i], NORM_INF)) << "frame " << i;
}
}
#endif // HAVE_PNG
#if defined(HAVE_PNG) || defined(HAVE_SPNG)