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JP4 format

So we have added a special JP4 mode that bypasses the Demosaic in the FPGA and provides an image with pixels in each 16x16 macroblock that are rearranged to separate Bayer colors in individual 8x8 blocks, then encoded as monochrome. Demosaic will be applied during post-processing on the host PC. This section describe different algorithms and implementations used to provide this functionality.

Main goals:

- compression speed improvement
- possibility to obtain more high quality image (near to RAW)
- drasticaly lowering data size

Image decoding

JP4 format can be easy manipulated by Matlab
JP4 image

1. Read image

I=imread('hdr02.jp4'); %read JP4 file like JPEG
I=I(:,:,1);            %strip color data
2. Remove block grouping
Bayer CFA encoded image
II=deblock16x16(I);    %deblock image
%file deblock16x16.m
function y=deblock16x16(I)
for x=1:16:size(I,1)
  for y=1:16:size(I,2)
      for dx=0:7
        for dy=0:7
          y0(x+2*dx  ,y+2*dy)   = blk16(dx+1,dy+1);
          y0(x+2*dx+1,y+2*dy)   = blk16(dx+9,dy+1);
          y0(x+2*dx  ,y+2*dy+1) = blk16(dx+1,dy+9);
          y0(x+2*dx+1,y+2*dy+1) = blk16(dx+9,dy+9);
2. Demosaic image (Decode from Bayer CFA (Color Filter Array) encoded image)
Decoded image

3. Show image


Stream decoding

JP4 stream can be decoded by mplayer. Use this patch for glue libdc1394 and mplayer video filter frontend.

Debayer ([Demosaic_on_client_side|Demosaic]) algorithm variants provided by libdc1394:
- Nearest Neighbor
- Simple AVT
- Bilinear
- HQLinear
- Downsample
- Edge Sense II
- Linear
- fast Linear


Bayer pattern look like this

R G1 R G1 R G1
G2 B G2 B G2 B
R G1 R G1 R G1
G2 B G2 B G2 B
R G1 R G1 R G1
G2 B G2 B G2 B

Some sensors have possibility to set independed scale to G1 and G2. Considering that the accessible optics does not give the full permission of a sensor resolution, it can be used for increase in a dynamic range of a image sensor.