Tuesday, December 13, 2011

Improving the Dissolve effect

In a previous post [Link], the fade-in, fade-out, and dissolve effects were described and computed in ImageJ for static images. Here are two main improvements...

1- Dissolve effect between two video clips (stacks).

Our previous examples have been done with static images, it's useful to calculate this effect between two video clips ... 

Download the two samples stacks (in TIF format) here and there. 

You have to split the stacks in two parts: video#1 between the transition and during transition, video #2 during transition and after transition.

2- Interpolation scheme

The second improvement corresponds to the transition speed between the two images (or video clips...)

Fig.2: Starting images for dissolve effect.

By default, the dissolve effect via the Scale function of ImageJ only allows linear interpolation as shown if you compute the Z-plot (Image > Stacks > Plot Z-axis Profile) of the stack generated from montage of Fig.2. At the beginning, the pixels are black (v=0) and are linearly increasing up to reach the values of the second image.
Fig.3: Time (Z-) plot. At frame 0, the selected pixels are black and are linearly evolving to a light gray pixel (frame 40).

Sometimes, you need a faster transition and need an interpolation following a sigmoid curve. In that case, the transition begins slowly, becomes faster during the transition and slows down at the end.

Hope that helps...

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