diff --git a/ffv1.md b/ffv1.md index f93a7f2..939824f 100644 --- a/ffv1.md +++ b/ffv1.md @@ -294,7 +294,7 @@ 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. Both color spaces 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. @@ -395,6 +395,10 @@ 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] +### Color Filter Array + +(TODO) + ## 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: @@ -722,6 +726,10 @@ Parameters( ) { | for (i = 1; i < 256; i++) | state_transition_delta[ i ] | sr colorspace_type | ur + if (colorspace_type == 2) { | + for ( i = 0; i < 4; i++ ) { | + cfa_pattern [ i ] | ur + } | if (version >= 1) | bits_per_raw_sample | ur chroma_planes | br @@ -810,16 +818,42 @@ 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 | Color Filter Array | JPEG2000-RCT | Color difference | `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, transparency MUST be 1. + +### 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 | + +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