I want to know some information about YV12 image format.
1st question is YV12 Image format is equal to YUV420p format or YVU420p or YUV420Sp or YVU420Sp. I know that U and V have the same amount of memory in the format so in the case of planer image formats does swapping U and V makes some major difference. and if it does can some body explain me what is that.
Also i have heard that YV12 and NV12 are both 12 bits formats. Then can some body tell me that what is 4:2:0? it will be great if some can explain me in simple words thanks
According to this site, YV12 looks the same as NV12 except that NV12 is interleaved and YV12 is not. I think that YV12 correspond to YVU420p and NV12 is YVU420sp, but I'm not 100% sure about that.
What this means however, is that instead of having triplets [yuv][yuv][yuv][...] repeated all over your buffer to draw the image, one triplet per pixel, you have a large buffer of [y], then a buffer 1/4 of the [y] size containing all the [u], then another one 1/4 of [y] containing the [v]. For an image of 320x240 (76800 pixels), you will have 76800 Ys at the start of your buffer, then 19200 Us, then 19200 Vs.
In the NV12 case, you have a large buffer of [y], then a buffer 1/2 of the [y] size containing [uv] pairs. When drawing the image, or converting to another format such as RGB, you need a least 2 pointers, one that will read Ys and another one that will read the Us and Vs
When reading such as compressed format, the trick is that you have one Y per pixel, but the UV components change only on odd rows and odd columns and your eye will not see the difference. You reuse the same UV values for 4 pixels at a time while changing the Y for every pixel.