search

MPEGGroup / FileFormat

MPEG file format discussions
24 stars 0 forks source link

HEIF mirroring interpretation #22

Closed cconcolato closed 3 years ago

cconcolato commented 3 years ago

The spec says: "axis specifies a vertical (axis = 0) or horizontal (axis = 1) axis for the mirroring operation."

One interpretation is that: when axis = 0, the axis for the mirroring is vertical and therefore the left of the image becomes the right and the right becomes the left. Similarly, when axis is 1, the axis is horizontal and the bottom becomes the top and vice versa.

Another interpretation is that a vertical mirroring (0) is when the image is modified vertically, i.e. when the bottom becomes the top and vice versa.

How do people implement it?

dwsinger commented 3 years ago

I think I need to apologize here; I was thinking the first when I wrote the text; but I should have been aware that EXIF uses the terms horizontal and vertical mirroring, which use the words horizontal and vertical in the second sense, which was going to, and has, caused confusion. I'm sorry.

joedrago commented 3 years ago

@ledyba-z I suspect this potential misunderstanding impacts your test images that use the imir transformation. I updated some of my documentation/syntax/headers to make libavif/avifenc much clearer too, as well as correcting my implementation in Vantage.

dwsinger commented 3 years ago

being addressed in amendment.2, closing