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[WIP] Add Color Filter Array (Bayer) #100

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55 changes: 46 additions & 9 deletions ffv1.md
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Expand Up @@ -45,6 +45,8 @@ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "S

`RGB`: A reference to the method of storing the value of a `Pixel` by using three numeric values that represent Red, Green, and Blue.

`RGGB Color Filter Array`: A reference to the method of storing the value of a `Pixel` by using four numeric values that represent Red, Green, Blue, and Green Difference.

`YCbCr`: A reference to the method of storing the value of a `Pixel` by using three numeric values that represent the luma of the `Pixel` (Y) and the chrominance of the `Pixel` (Cb and Cr). YCbCr word is used for historical reasons and currently references any color space relying on 1 luma `Sample` and 2 chrominance `Samples` e.g. YCbCr, YCgCo or ICtCp. Exact meaning of the three numeric values is unspecified.

`TBA`: To Be Announced. Used in reference to the development of future iterations of the FFV1 specification.
Expand Down Expand Up @@ -294,7 +296,7 @@ Background: in first implementations of FFV1 bitstream, the index for Cb and Cr

## Color spaces

FFV1 supports two color spaces: YCbCr and RGB. Both color spaces allow an optional Alpha `Plane` that can be used to code transparency data.
FFV1 supports several color spaces. They allow an optional Alpha `Plane` that can be used to code transparency data.

The FFV1 bitstream interleaves data in an order determined by the color space. In YCbCr for each `Plane`, each `Line` is coded from top to bottom and for each `Line`, each `Sample` is coded from left to right. In JPEG2000-RCT for each `Line` from top to bottom, each `Plane` is coded and for each `Plane`, each `Sample` is encoded from left to right.

Expand Down Expand Up @@ -395,6 +397,10 @@ In JPEG2000-RCT, the coding order would be left to right and then top to bottom,

Y[1,1] Y[2,1] Cb[1,1] Cb[2,1] Cr[1,1] Cr[2,1] Y[1,2] Y[2,2] Cb[1,2] Cb[2,2] Cr[1,2] Cr[2,2]

### RGGB Color Filter Array

(TODO)

@dericed dericed Oct 16, 2018

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what coming here?

@JeromeMartinez JeromeMartinez Oct 16, 2018

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Some general introduction to CFA, order of planes... as for the 2 other colors spaces.


## Coding of the Sample Difference

Instead of coding the n+1 bits of the Sample Difference with Huffman or Range coding (or n+2 bits, in the case of JPEG2000-RCT), only the n (or n+1, in the case of JPEG2000-RCT) least significant bits are used, since this is sufficient to recover the original `Sample`. In the equation below, the term "bits" represents bits_per_raw_sample+1 for JPEG2000-RCT or bits_per_raw_sample otherwise:
Expand Down Expand Up @@ -745,6 +751,10 @@ Parameters( ) { |
} |
ec | ur
intra | ur
if (colorspace_type == 2) { |
for ( i = 0; i < 4; i++ ) { |
cfa_pattern [ i ] | ur
} |
} |
} |
```
Expand Down Expand Up @@ -810,16 +820,42 @@ If state_transition_delta is not present in the FFV1 bitstream, all Range coder

### colorspace_type

`colorspace_type` specifies the color space losslessly encoded, the Pixel transformation used by the encoder, as well as interleave method.
`colorspace_type` specifies the color space encoded, the pixel transformation used by the encoder, the extra plane content, as well as interleave method.

|value | color space losslessly encoded | transformation | interleave method |
|-------|:--------------------------------|:--------------------------------|:--------------------------------|
| 0 | YCbCr | No Pixel transformation | `Plane` then `Line` |
| 1 | RGB | JPEG2000-RCT | `Line` then `Plane` |
| Other | reserved for future use | reserved for future use | reserved for future use |
|value | color space encoded | pixel transformation | extra plane content | interleave method |
|-------|:------------------------|:------------------------|:------------------------|:------------------------|
| 0 | YCbCr | None | Transparency | `Plane` then `Line` |
| 1 | RGB | JPEG2000-RCT | Transparency | `Line` then `Plane` |
| 2 | RGGB Color Filter Array | JPEG2000-RCT | Transparency | `Line` then `Plane` |
| Other | reserved for future use | reserved for future use | reserved for future use | reserved for future use |

Restrictions:
If `colorspace_type` is 1, then `chroma_planes` MUST be 1, `log2_h_chroma_subsample` MUST be 0, and `log2_v_chroma_subsample` MUST be 0.
If `colorspace_type` is 2, then `chroma_planes` MUST be 1, `log2_h_chroma_subsample` MUST be 0, and `log2_v_chroma_subsample` MUST be 0.

### cfa_pattern

`cfa_pattern` indicates the actual color filter array geometric pattern of the image sensor used to capture the single sensor color image.
The pattern has a fixed size of 4 values (fixed width of 2, fixed height of 2) and is provided per line top to bottom, and for each line left to right.

|value | color |
|-------|:--------------------------------|
|0 | red |
|1 | green |
|2 | blue |
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Restrictions:
At least 1 component of each color MUST be present.

As an example, a typical pattern is 0112, which implies:

```
+---+---+
| R | G |
+---+---+
| G | B |
+---+---+
```

### chroma_planes

Expand Down Expand Up @@ -1161,7 +1197,8 @@ SliceContent( ) { |
for( p = 0; p < primary_color_count; p++ ) |
for( y = 0; y < plane_pixel_height[ p ]; y++ ) |
Line( p, y ) |
} else if (colorspace_type == 1) { |
} else if (colorspace_type == 1 |
|| colorspace_type == 2) { |
for( y = 0; y < slice_pixel_height; y++ ) |
for( p = 0; p < primary_color_count; p++ ) |
Line( p, y ) |
Expand All @@ -1171,7 +1208,7 @@ SliceContent( ) { |

### primary_color_count

`primary_color_count` is defined as `1 + ( chroma_planes ? 2 : 0 ) + ( alpha_plane ? 1 : 0 )`.
`primary_color_count` is defined as `1 + ( chroma_planes ? 2 : 0 ) + ( colorspace_type == 2 ? 1 : 0 ) + ( alpha_plane ? 1 : 0 )`.

### plane_pixel_height

Expand Down