I propose to add simple performance test.

An animation with 1 frame is not the same as one image (though it will be displayed the same).

An animation with 1 frame is not the same as one image (though it will be displayed the same).

It should be like that for webp and avif. But when an animated png saved with only one frame, the only thing that changes actually is being 10 times slower.

following code just writes IHDR and IDAT chunks like imwrite

    Mat m(2000,3000,CV_8UC4);
    Animation tanimation;
    tanimation.frames.push_back(m);
    tanimation.durations.push_back(10);
    imwriteanimation("read_c.png", tanimation);c

anyway let me work on this PR a bit more. creating a performans test and maybe rethinking on one frame apng

it was Z_BEST_COMPRESSION used for writing ( even writing with IMWRITE_PNG_COMPRESSION param)
now Z_BEST_SPEED ( 1 ) is default and IMWRITE_PNG_COMPRESSION param works

@sturkmen72 Please rebase and fix conflict after you PR merge.

@asmorkalov i will try to write tests using PngSuite - Image filtering / PNG-files

Ok, please try to use existing files in opencv-extra and do not add more. We have some subset of the suite already.

@sturkmen72 Please rebase and fix conflicts.

@vrabaud I'm ready to merge the patch. Do you have any remarks?

@vrabaud Please take a look again.