GStreamer Pan Tilt Zoom and Rotate Element - Zoom

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This page serves as a reference on how to adjust zoom values on GstPTZR.

Zoom Levels

The zoom effect is achieved by taking a capture region of different sizes, and scaling it to the output size. Taking a smaller capture region, will require an upscale and pixel interpolation, achieving the zoom in effect. On the other hand, taking a bigger capture region will require a downscale, hence, the zoom out effect. The following sections describe in more detail each zoom configuration. To do so, the following standard is used:

in-size
The size of the input image
out-size
The size of the output image
zoom-level
The value currently configured in the zoom

zoom-level = 1

When zoom-level is set to 1, there is no magnification expected. Hence, a region of size out-size will be taken from the input image. No scaling is required to fit the capture region in the output image, since both match out-size. Figure 1 exemplifies this concept.

Figure 1. GstPTZR configured with zoom-level=1 on Bartok the Dachshund

0 <= zoom-level < 1

For values lesser than 1, zoom-level can take real values starting from 0. This limit value of 0 represents the biggest capture region that fits in the input image while maintaining the output image's aspect ratio. Figure 2 shows graphically this concept. For values in between 0 and 1, the capture region will vary accordingly. Note that, in this case, a downscale of the capture region is perform to fit out-size.

Figure 2. GstPTZR configured with zoom-level=0 on Bartok the Dachshund

zoom-level > 1

For values greater than 1, zoom-level is taken literally as a multiplication factor. For example, for a value of 2, half out-size is taken and upscaled. Internally, OpenGL will interpolate the pixels. The only upper bound defined to the zoom is for the case that the capture region is a single pixel. Figure 3 exemplifies this concept.

Figure 3. GstPTZR configured with zoom-level=2 on Bartok the Dachshund


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