Returns the number of horizontal scanlines in an image given the DXGI format and pixel height.
size_t ComputeScanlines( _In_ DXGI_FORMAT fmt, _In_ size_t height );
For most images, the number of scanlines is the same as the height of the image. For block-compressed (BC) images, the number of scanlines is 1/4 of the original height since each scanline contains 4x4 blocks. For planar images, this number can be 1.5x or 2x
the original height.