Support for YUVU source images

[danilostefani]

Hi, Thank you for your library. I needed to create a JPEG image from an YUVU image in memory, directly, without the overhead of transcoding in RGB back and forth. I Tryed to keep the modifications to your clean and nice code as little as possible... take a look and see if could be useful to others. Not extensively tested, at the moment.

[stbrumme]

Thanks for your contribution ! Currently I’m on a vacation and will take a look at your code when I come back home (mid-May). At first glance it’ll probably make sense to support YUV444 (input) as well. Have a nice day, Stephan

[antonysigma]

Wow! I thought no one would care to encode JPEG directly from YUV444 or YUV420 buffer.

I do have a similar patch to support YUV420 buffer input with custom padding/stride between Y colorspace and UV colorspace. I will prepare a PR then.

By the way, @stbrumme, could you suggest a best practice to pass the following info to the toojpeg API?

• 8-bit U and V values needs an offset prior to JPEG compression, i.e. uint8_t corrected_U[i][j] = uint8_t(U[i][j]) - 128
• "horizontal" / "vertical" paddings, as shown in the illustration below; and

Edit: There is a very similar question at https://github.com/stbrumme/toojpeg/issues/5.

    +-------------------------------------------+
    |-------------------------------+           |
    ||                              |           |
    ||                              |           |
    ||            Y space           |  right    |
    ||                              |  padding  |
    ||                              |  for      |
    ||                              |  alignment|
    +-------------------------------+           |
    |     padding between Y and UV              |
    |                                           |
    +-------------------------------+           |
    ||           UV space           |           |
    ||                              |           |
    |-------------------------------+           |
    +-------------------------------------------+