QOI - The “Quite OK Image Format” for fast, lossless image compression.

More info at https://qoiformat.org.

QOI targeted to FPGAs

Verilog

Fully featured encoder and decoder, all QOI_OPs supported according to the spec.

Testing

Verilator is able to emulate the fpga logic on a computer and is embeddable in C, enough for it to be a drop in qoi_{encode,decode} replacement for some of the reference implementation.

Run make VERILATED=1 test_encode, it will convert an image to qoi and then use the system converter to convert back (both ours and the reference .qoi). The md5sums of the resulting png files should match (it should mean all pixels survived being encoded), the md5sums of the .qoi files should also match if it's a full featured encoder.

Run make VERILATED=1 test_decode for a similar test exercising the decoding.

LiteX

Coming soon!

Connections

Encoder

Input

The rgba pixel data with a clk.

If image is in 3 channel mode, an alpha of 0xff must still be provided as encoder is always in 4 channel mode. Though if the alpha does not change from 0xff as it's encoding, it will produce only 3 channel QOI_OPs.

On the next clock after the last pixel please send a high finish so the encoder can immediatelly commit any QOI_OP_RUN that are in progress.

Output

The encoder will usually output a whole QOI chunk (1-5 bytes), though delayed by one clock cycle (to account for any QOI_OP_RUN). If Alpha is not needed the max chunk size is 4 bytes, which might fit in a single memory transaction.

chunk_len specifies how many bytes the current chunk contains, could be 0 bytes in case of QOI_OP_RUN for many pixels, could be as high as 5 when we have a fresh RGBA pixel.

This will eventually need to connect to some kind of bus like AXI or Avalon. Not really sure how to deal with the variable length output from the encoder yet.

Decoder

Input

A way to peek at the next chunk (5 bytes if RGBA, or 4 for just RGB).

For every clock the decoder will output how many bytes it "ate" via chunk_len_consumed,

This value can be used to advance the peek pointer (or sometimes even stay in the same spot for a while in case of QOI_OP_RUN).

Output

One RGBA pixel per clock.