Complete Communications Engineering

A Basic Video Scaler increases the input resolution for video output at the specified ratio. Video Scaling is essential for video processing devices where the output resolution must be greater than the input resolution by some rational value.

Fig. 1 Scaling Video using polyphase vertical and horizontal filters

A common approach to video scaling is to use polyphase filters independently in the vertical and horizontal directions. A Polyphase filter could be described as 2-D array of coefficients. The number of rows of this array m is equal to the number of phases. Each row represents the individual FIR filter. The number of elements in the row (i.e. the number of columns) is a length of each FIR.

To get the output pixel value, the phase of the location of this pixel with respect to the input pixel grid is computed. The actual phase of the output pixel may have any rational value. Each phase of the polyphase filter corresponds to a quantized value of the output pixel phase. The number of phases m defines the precision of the phase quantization.

After the phase is calculated and quantized to m levels, only the one FIR that corresponds to the quantized phase is utilized to calculate the output pixel value.

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