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Memory Reduction
It is much faster to track, and check tracking, when the shot is entirely in the PC’s RAM memory, as fetching each image from disk, and possibly decompressing it, takes an appreciable amount of time. This is especially true for film-resolution images, which take up more of the RAM, and take longer to load from disk.
SynthEyes offers several ways to control RAM consumption, ranging from blunt to scalpel-sharp.
The most important control is the Max RAM Cache GB preference in the Image Input section. It controls how many frames of the shot are stored in your computer's RAM. This can be much lower than the length of the shot. If you are auto-tracking, keep at least two frames per processor (four if your processors are hyper-threaded, ie two per usable thread). If you are seeing swapping on a 64-bit license, reducing the MAX RAM Cache GB should be your first move, and can generally be your last. (If your system says it is running out of memory, check for plenty of free disk space on your main system disk!)
A reduced RAM cache will mean that your computer will have to go out to fetch images from disk more often. That can be painful for some movie codecs. If you want
fast interactive performance, but are willing to give up some other things in order to fit your shot into RAM, read on.
If your source images have 16 bit data, you can elect to reduce them to 8 bit for storage, by unchecking the 16-bit checkbox and reducing memory by a factor of two. Of course, this doesn’t help if the image is already 8 bit.
If you have a 2K or 4K resolution film image, you might be able to track at a lower resolution. The DeRez control allows you to select ½ or ¼ image resolution selections. If you reduce resolution by ½, the storage required drops to ¼ the previous level, and a reduction by ¼ reduces the storage to 1/16 th the prior amount, since the resolution reduction affects both horizontal and vertical directions. Note that by reducing the incoming image resolution, your tracks will have a higher noise level which may be unacceptable; this is your decision.
If you can track using only a single channel, such as R, G, or luma, you obtain an easy factor of 3 reduction in storage required.
The most precise storage reduction tool is the Region Of Interest (ROI) , which preserves only a moving portion of the image that you specify, and makes the rest black. The black portion does not require any RAM storage, so if the ROI is only 1/8 th the width and height of the image, a reduction by 1/64 th of storage is obtained.
Tip : If you need ROI these days, likely you should just get some more memory! It was originally intended for processing film images on 32-bit machines. This feature is subject to future removal! It may be useful for processing padded 360VR images, ie 360x120 to 360x180.
The region of interest can be used with object-type shots, such as tracking a face or head, a chestplate, a car driving by, etc, where the interesting part is comparatively small. The ROI can also be used in supervised tracking, where the ROI can be set up for a region of trackers; once that region is tracked, a different ROI can be configured for the next group. A time savings can be achieved even though the next group will require an image sequence reload. (See the section on presets, below, to be able to save such configurations.)
The ROI is controlled by dragging it with the left mouse button in the Image Preprocessor dialog’s viewport. Dragging the size-control box at its lower right of the ROI will change the ROI size.
The next section describes animating the preprocessor level and ROI.
It can also be helpful to adjust the ROI controls when doing supervised tracking of shots that contain a non-image border as an artifact of tracking. This extra border can defeat the mechanism that turns off supervised trackers when they reach the edge of the frame, because they run out of image to track before reaching the actual edge.
Once the ROI has been decreased to exclude the image border, the trackers will shut off when they go outside the usable image.
As with the image adjustments, changing the memory controls does not require any re-tracking, since the image geometry does not change.
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