022

This is not a post, as to why Mumbai has 022 as its dialing code. 022 is the name of the utility that I concocted during the spare time at work that I am having these days.
It stands for “ 0 to(2) 2 ”,with 0 as in 4:2:0 and 2 as in 4:2:2. Now, 4:2:0 and 4:2:2 are two formats for representing raw video data in digital format. The three numbers represent the luminance (Y), and chrominance (U, V) information respectively. The difference between them is in the amount of chroma information that is stored. In 4:2:0, the resolution of the chroma samples is halved in both the vertical and horizontal directions. For instance if your luma information is represented as 176 x 144 pixels, each of the chroma samples, U and V are 88 x 72 pixels. On the other hand (It feels quite funny to use this expression – “On the other hand”, but nevertheless..), in 4:2:2 the chroma samples are halved in only the horizontal direction. So in 4:2:2 , the chroma samples are 88 x 144 pixels each. Then there is also the 4:4:4 format where the amount of chroma information stored is the same as the amount of luma stored. The chroma information, then, in 4:4:4 is 176 x 144 pixels. Don’t bother too much about why the number “4” is used to represent the various formats. There is some reason, which I cannot recollect right now. Its not too significant in this context,either.

So what is the fuss about having so many different formats to store the YUV. Supposedly, the human eye is more sensitive to the luminance aspect of an image than the chroma information. To take advantage of this weakness, they have resorted to the various formats. An image in 4:2:0 requires half the number of bytes than that required by an image in 4:4:4 without much loss (actually any) in visual perception.

Finally, what does 022 do. Not much actually. It takes a YUV file in 4:2:0 format and converts it into 4:2:2. How does it do it? Well there are a number of ways like interpolation, replication and so forth. 022 being simple, just uses the replication method wherein the pixels are replicated line by line vertically. There, you have the 4:2:2 file as output. This talks about converting from 4:2:0 to 4:2:2 using interpolation.

In all probability, this could be my first and last post on a technical issue. There are sites reserved for technical discussions and I feel this is not the right place. You can interpret that, as a euphemism for saying, “ I am dumb, so please do not expect anything technical from me”.