220.127.116.11.1.1 Performing the First Progressive Pass
For the first pass, the data received is sent to the RLGR entropy decoder to produce the progressively quantized coefficients DecProgQ.
For each element being decoded, except elements in the LL band, the sign is recorded (positive, negative, or zero). This tri-state (referred to as Sign) is used for successive upgrade passes.
Sign = -1 if DecProgQ-NonLL < 0
Sign = 0 if DecProgQ-NonLL = 0
Sign = 1 if DecProgQ-NonLL > 0
The LL3 deltas MUST be summed up to produce the LL3 elements, even if the tile is not an original tile (section 18.104.22.168.2).
DecProgQ-LL = DecProgQ-LL-Deltas
DecProgQ-LL[idx+1] = DecProgQ-LL[idx] + DecProgQ-LL-Deltas[idx+1]
Elements in all the bands are dequantized.
DecDwtQ-NonLL, DecDwtQ-LL = DecProgQ * PQF
DecDwtQ is the data that MUST be de-quantized and inverse DWT transformed to produce the image pixels.
If the tile is a difference tile (section 22.214.171.124.2), then the progressively quantized coefficients are simply added to the DecDwtQ elements:
DecDwtQ = DecDwtQ + DecProgQ * PQF