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Set Wallpaper
Set the system (home screen) wallpaper from an SD card image file.
JPG and PNG are supported.
If no image is specified, the default system image is set.
Scale: if the image is smaller in width or height than the launcher-specified values, scale it up to those values while keeping the aspect ratio.
Crop: if the image dimensions (possibly after scaling) are greater than the launcher-specified values crop it down to those dimensions. This can be necessary to prevent Android-internal problems.
Note that it can take more than 20 seconds for this action to take effect.