Size
The size setting refers to the image resolution in pixels. A higher image resolution allows you to print that image in larger sizes without degrading the image quality.
The bigger the number of recorded pixels is, the better the image quality becomes. As the number of recorded pixels lessen, you will be able to record more images on a memory card.
OIS
This mode can help reduce photo blur caused by unintentional hand shake, low light or slow shutter speed.
Use Stabilization Mode in dark environments or when using a slower shutter speed.
Shooting in a windy or unstable environment (such as a moving vehicle) may cause blurred images.
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