F_Align and F_Steadiness work in a similar way, which is distinct from the way F_RigRemoval works. These two effects calculate a four-corner pin for each frame and save it into the corner pin parameters. These pins are then used during the render to move the source image.
These effects analyze images over a range of frames to figure out their four-corner pins. This is done in response to the user pressing the Analyse button in the effects control panel. During analysis, the effect will run through a range of frames adding keys to the corner pin parameters. These corner pins are then applied to the source clip to render a frame.
F_Steadiness has a separate analysis pass that happens interactively; it then uses the previously computed and key-framed corner pins during render. This speeds up its operation, as the analysis step only has to be done once, and once it has been done this plug-in is very quick to render. However, F_Align, which only ever needs the two current frames from each clip, can compute the corner pin on the fly (but not keyframe it!). This leads to a slightly different mode of operation for the following effects:
• F_Steadiness
• needs to have an analysis run before it renders useful output,
• will always use the value in the corner pin parameters when rendering the output image.
• F_Align
• no need to have the analysis run to render output, but doing so will give you a key-framed corner pin,
• during render, it will use the value of the corner pin parameters only if there is a keyframe there, otherwise, it will analyse on the fly during render. This means that analysis will speed up later renders, as just rendering the corner pin is much cheaper than calculating it.
Some parameters to the effect control how the effect performs GME analysis, and some only affect the rendering. If you ever modify one of these parameters, then any analysis you may have performed will be out of date. To let you know, an overlay warning will be posted whenever this happens. You don’t have to re-analyze and your renders will still look at the keyed corner pins.
If you have not modified a parameter that affects analysis (the warning overlay will let you know), pressing Analyse will only re-analyse a frame if there is no key on the corner pin at that time. This avoids redundant re-analysis if you have interrupted the analysis or extended the analysis range. However, if you want to force re-analysis, press Clear Analysis and all keys will be deleted.
F_Steadiness and F_Align have an analysis region rectangle parameter which is used to specify which area of the reference image should be analysed during GME. So, for example, with F_Steadiness set to Lock Mode, this is the area inside the lock frame that a match will be sought for. The documentation for each plug-in describes exactly how to use the analysis region.