.RW2 File Format – Tags and raw data

Panasonic tags in IFD 0

Standard tags in IFD 0 include Make (0x010F), Model, StripOffsets (0x0111), Orientation, RowsPerStrip, StripByteCounts, Artist, XMP (0x02BC), Copyright, IPTC, and the Exif and GPS IFD pointers.

Sub-tables

• WBInfo (0x0013): shorts. Index 0 is the number of entries; then up to seven pairs of a light source type (Exif LightSource codes) and red and blue levels.
• WBInfo2 (0x0027): the same, with red, green and blue levels for each entry.
• DistortionInfo (0x0119): signed shorts of distortion parameters and a scale; the low 4 bits of one field switch the correction off (0) or on (1). The model behind the parameters is not documented.
• CameraIFD (0x0120): an IFD with tags such as 0x1201 and 0x1202 (lens make and model), 0x1301–0x1303 (aperture, shutter speed, sensitivity), 0x3200–0x3203 (daylight white balance per CFA colour) and 0x3300 (white balance set: 0 auto up to 16).

Raw data

The sensor data starts at RawDataOffset (or StripOffsets). Older RW2 files are either unpacked or use the original Panasonic compression below, which dcraw decodes. Newer cameras use further coding versions (RawFormat values beyond the original), supported in LibRaw but not publicly specified; they are not described here.

The original compression reads the data in blocks of 16384 bytes. Each block is stored rotated: to rebuild it, move its last 0x2008 bytes to the front. Bits are then read with a position p that starts at 0 for each block and, for each read of n bits, becomes (p − n) mod 0x20000; the bits are taken from the 16-bit little-endian value at byte (p >> 3) XOR 0x3FF0, shifted right by p mod 8. Each row is coded in groups of 14 pixels, with a predictor for even and one for odd columns:

at the start of each 14-pixel group:  pred[0] = pred[1] = nonz[0] = nonz[1] = 0
for each pixel, i = column mod 14, c = i mod 2:
  if i mod 3 == 2:  sh = 4 >> (3 - read 2 bits)
  if nonz[c]:
      j = read 8 bits
      if j != 0:
          pred[c] -= 0x80 << sh
          if pred[c] < 0 or sh == 4:  pred[c] &= (1 << sh) - 1
          pred[c] += j << sh
  else:
      nonz[c] = read 8 bits
      if nonz[c] != 0 or i > 11:  pred[c] = nonz[c] << 4 | read 4 bits
  value = pred[c]

Values are 12-bit. The pixels of each row are all coded, including any beyond the visible width.