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Line scope

The Line-scope is an interactive signal inspection tool within decode-orc that allows detailed examination of individual video lines at the sample level. Like the Preview dialogue, it is not a pipeline stage, but a UI analysis tool that attaches to preview-capable stages.

The Line-scope is primarily intended for low-level signal analysis, making it possible to inspect timing, levels, noise, burst structure, and dropout behaviour with precision that is not possible from image-based preview alone.

Purpose and use cases

The Line-scope is used to:

  • Inspect raw luma and chroma waveforms
  • Verify black, white, and sync levels (IRE)
  • Examine colour burst amplitude and phase
  • Diagnose noise, ringing, or capture artefacts
  • Validate dropout detection and correction behaviour
  • Compare line data before and after transform stages

It is especially valuable when working with:

  • Analogue captures
  • LaserDisc RF-derived signals
  • PAL/NTSC timing and level issues
  • Dropout-heavy or marginal sources

Attaching the line-scope

The Line-scope attaches to the currently previewed stage and reflects the same field and timing context as the Preview dialogue.

When active, it operates on:

  • The currently selected field
  • A single selected field line
  • The post-stage output signal (including all upstream transforms)

Core line-scope features

Line selection

The user can select a specific field line index to inspect.

Key characteristics:

  • Line numbering is field-relative
  • Line indices reflect any upstream re-mapping or masking
  • First/second field parity is respected

This makes the Line-scope suitable for inspecting:

  • VBI lines
  • Active video lines
  • Masked or corrected regions

Sample-level waveform display

The Line-scope displays signal amplitude per sample across the selected line.

The waveform typically includes:

  • Sync tip
  • Back porch
  • Colour burst (if present)
  • Active video region

Amplitude is shown in IRE-scaled units derived from the effective video parameters.

Channel views

Depending on pipeline configuration and stage capabilities, the Line-scope may support viewing:

  • Luma (Y)
  • Chroma (composite or decoded)
  • Combined signal (where applicable)

The exact available channels depend on the upstream stages and signal type.

Interaction with transform stages

The Line-scope reflects exactly what a downstream stage will see.

Examples:

  • After video_params, black/white level overrides are visible immediately.
  • After mask_line, masked regions appear flattened at the mask IRE level.
  • After dropout_correct, corrected samples can be inspected directly.
  • After stacker, per-sample noise reduction effects are visible.

This makes the Line-scope ideal for validating the numerical effect of transforms.

Dropout and correction inspection

When dropout hints are present, the Line-scope can be used to:

  • Inspect the original corrupted samples
  • Verify the extent of dropout regions
  • Confirm that replacement data is reasonable
  • Compare corrected vs uncorrected behaviour by toggling upstream stages

When highlight_corrections is enabled upstream, corrected regions appear clearly in the waveform.

Timing and stability analysis

The Line-scope is frequently used to:

  • Verify horizontal timing stability
  • Inspect sync edge shape and jitter
  • Check burst placement and consistency
  • Compare timing between aligned sources

These checks are essential when diagnosing capture hardware issues or alignment problems.

Limitations

  • The Line-scope is read-only and non-destructive.
  • Only one line can be inspected at a time.
  • Performance depends on pipeline complexity and preview position.
  • Some sink-only or hardware-output stages do not support line-scope attachment.

Typical line-scope workflows

Common workflows include:

  • Inspecting colour burst before and after chroma-related transforms
  • Verifying black/white levels after video_params
  • Examining dropout regions before applying correction
  • Comparing stacked vs unstacked signal noise
  • Diagnosing capture artefacts at the sample level

Notes on line-scope usage

  • The Line-scope always reflects the current preview field and stage.
  • Line-scope analysis complements, rather than replaces, image-based preview.
  • For accurate interpretation, ensure video parameters upstream are correct.

The Line-scope is a critical tool for decode-orc’s low-level, signal-focused workflows, providing visibility into the exact waveform data that underpins all higher-level processing.