UltimateSlice

Colour Scopes

UltimateSlice includes a professional colour scope panel to help you evaluate your grade objectively. The panel lives below the Program Monitor and is toggled with the “▾ Scopes” button.

Showing / Hiding the Scopes

Click the ▾ Scopes button just below the Program Monitor to reveal or hide the panel. The panel slides in with an animation and disappears completely when hidden (freeing vertical space).

Frames are only captured and analysed while the panel is visible — no CPU is wasted when it is hidden.

Scope Modes

Switch between modes using the tab strip at the top of the scopes panel.

Waveform

Plots the luma (brightness) of every pixel at its horizontal position in the frame.

  • Bright pixels appear near the top (high IRE).
  • Dark pixels appear near the bottom (low IRE).
  • Graticule lines are drawn at 0 %, 25 %, 50 %, 75 %, and 100 %.

Use the waveform to set exposure, check for crushed blacks or clipped whites, and match shots.

Histogram

Shows the distribution of luma values from 0 (black) to 255 (white) as a bar chart. A healthy exposure typically produces a well-spread, roughly bell-shaped histogram that does not clip hard at either end.

RGB Parade

Three side-by-side waveform monitors — one each for the Red, Green, and Blue channels. Use the parade to detect colour casts: if one channel’s waveform sits higher or lower than the others in the same region of the frame, that channel is biased.

Vectorscope

Plots Cb (U) vs Cr (V) chrominance for every pixel in a circular diagram.

  • The centre represents neutral (no saturation).
  • Distance from centre indicates saturation.
  • Angle indicates hue.

Use the vectorscope to match skin tones across shots and verify colour fidelity.

Underlying Architecture

Colour scope frames are captured by a small appsink (320 × 180 RGBA) connected via a GStreamer tee inside the program player’s video-sink bin. The tee branches to both the display (gtk4paintablesink) and the scope appsink simultaneously. The appsink uses drop=true, max-buffers=1 so it never stalls playback.

Frame analysis and Cairo drawing happen on the GTK main thread inside the existing 33 ms poll timer.