… for Apple Motion

Tip #1227: Compare Two Images for Artifacts

Larry Jordan – LarryJordan.com

Differences caused by compression are very subtle and confined to edges.

A significantly enhanced difference map highlighting differences between images.

Topic $TipTopic

Ever wonder what happens to your images when they are compressed? Well, Motion has a elegant way to illustrate these differences. Here’s how to discover them.

  • Import the two clips or stills you want to compare – this works for both video and stills.
  • Select the top clip.
  • In the Inspector, change Properties > Blend mode to Difference.

The first thing you’ll notice is that differences are VERY slight.

To enhance these results, apply Filters > Color > Levels to the GROUP that holds both images. Then drag the mid-tone slider to the left. This boosts the difference results.

Anything showing gray is different between the two images. Again, you’ll see the big difference is edge definition.

EXTRA CREDIT

If you want to be extra precise, bring these images into your favorite NLE and compare them using the Waveform Monitor.

Two identical images would show a solid black line at 0.


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