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Generate image deltas

An image delta shows, pixel by pixel, how a surface plot differs between two Attitudes. It's generated from the existing plot images, so there's no need to reprocess either simulation.

Before you start

  • Image deltas work on Plots only. Movies aren't supported.
  • Delta values are recovered from the plot's colours, so the plots should use a continuous, 256-level palette. A banded palette, such as 31 levels, gives coarse, banded deltas. Palettes are set on the Postpro Settings page, Palette tab, Number Of Levels column. The plots need to have been generated with that palette.

Generate the deltas

  1. On the Results page, select Attitudes from at least two Runs, including the one you'll use as the baseline.
  2. Under Available Postpro → Plots, click the variable to compare. The postpro viewer opens.
  3. Click Generate Image Deltas. It appears while you're viewing Plots from more than one Run.
  4. In Generate Image Delta Plots:
    • Variable: the plot variable(s) to compare.
    • Camera: the view(s).
    • Delta Baseline: the Attitude to compare against.
    • Attitude: the Attitude(s) to compare with the baseline.

  5. Optionally, tick Show Advanced Settings and set:

    • Palette: the colour scale for the delta. The default is "Delta Blue to Red, White Middle".
    • Black Sensitivity (0–250, default 0): how dark a pixel must be to count as a line or border rather than data.
    • Delta Range: Min and Max, default −0.2 and 0.2. Min must be less than Max.

    With Show Advanced Settings ticked, you can also choose from every variable and camera, not just the ones on screen.

    Warning

    Unticking Show Advanced Settings resets these values and your variable and camera choices. Leave it ticked when you submit.

  6. Click Submit.

Bramble generates the deltas in the background. There's no notification when they're ready. After a short while, select the Attitudes again on the Results page and look for the Image Deltas row in Available Postpro. Generating the same delta again replaces the old one.

View image deltas

  1. Select the Attitudes on the Results page.
  2. Under Available Postpro → Image Deltas, click the variable. The buttons use the original variable name, for example Cp.
  3. Use the Variables, Baselines, Delta Ranges and Palettes filters to choose which deltas to show.

Each image is captioned with the Attitude, variable and baseline, and with its palette and range. The delta images themselves have no legend. The colour means Attitude value minus baseline value, across the range you chose.

Related: Compare results in the postpro viewer · Results and post-processing