dualpass

Dualpass, often written dual-pass or two-pass, is a term used in computing to describe a processing strategy that completes data analysis in an initial pass and then uses the results of that analysis to guide a second pass that produces the final output. The two-stage approach enables more informed decisions, optimization, and better handling of dependencies that are difficult to resolve in a single pass. In practice, dual-pass systems appear in several domains, reflecting the common need to separate analysis from execution.

In compilers and assemblers, the first pass typically collects symbol definitions and addresses, while the second pass emits code with correctly resolved references. In image processing, two-pass connected-component labeling uses a first pass to assign provisional labels and record label equivalences, followed by a second pass to finalize the labeling. In video and audio encoding, two-pass rate control analyzes content in an initial pass to optimize bitrate distribution, then encodes in a second pass with the planned budget. In rendering, dual-pass or multi-pass rendering can separate scene setup, depth or shadow calculations, from shading and final output.

Disadvantages of dual-pass approaches include added latency and higher resource usage due to performing work twice. In some cases, single-pass or more than two passes may be preferable depending on data characteristics and performance constraints. The concept is general and appears across fields, where the first pass informs the second to improve quality, accuracy, or efficiency.