On the front page, I do not understand explanation of 4:2:2 etc

[vonj]

The text says "y is the number of changes of chroma samples between the first and seconds rows of a pixels."

But isn't it more accurate to say:

"y is the number of changes of chroma samples between the first and last rows of a pixels."

If not, I still don't understand how chroma subsampling is used!

[matteocontrini]

The sentence referes to the grid that is taken as a reference for chroma subsampling. When you say 4:*:* you mean a grid that has 4 columns and 2 rows (the 2 is fixed). So the y is the number of changes between the first row in the grid and the second row in the grid.

We had a discussion about chroma subsampling previously in #24, you might find useful reading it :)

[vonj]

So the grid is not always 4 by 4 pixels? I don’t know why I assumed that but I did...

…

25 juni 2019 kl. 18:33 skrev Matteo Contrini ***@***.***>: The sentence referes to the grid that is taken as a reference for chroma subsampling. When you say 4:*:* you mean a grid that has 4 columns and 2 rows (the 2 is fixed). So the y is the number of changes between the first row in the grid and the second row in the grid. We had a discussion about chroma subsampling previously in #24, you might find useful reading it :) — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or mute the thread.

[matteocontrini]

It's usually 4 by 2, with some uncommon exceptions like 4:1:0 and 4:2:1, according to Wikipedia.

[vonj]

I may create sample images of how I understand the situation... but later in that case.