Efficient down conversion system for 2:1 decimation

A method for forming a low resolution video signal from an encoded video signal representing a video image, the encoded video signal being a frequency-domain transformed high resolution video signal, the method comprising the steps of:

• (a) receiving the encoded video signal as a plurality of high resolution frequency-domain video coefficient values;
• (b) weighting a set of the plurality of high resolution frequency-domain video coefficient values to form a set of a respective plurality of low pass filtered frequency-domain video coefficients;
• (c) transforming the set of low pass filtered frequency-domain video coefficients into a first set of pixel values;
• (d) transforming selected ones of the pixel values in the first set of pixel values into averaged pixel values and providing a second set of pixel values including the averaged pixel values;
• and
• (e) deleting selected ones of the pixel values in the second set of pixel values to provide the low resolution video signal.

An apparatus for forming a low resolution video signal from an encoded video signal representing a video image, the encoded video signal being a frequency-domain transformed high resolution video signal, the apparatus comprising:

• receiving means for receiving the encoded video signal as a plurality of high resolution frequency-domain video coefficient values;
• down-conversion filter means for receiving and weighting selected ones of the plurality of high resolution frequency-domain video coefficient values to form a set of a respective plurality of frequency-domain video coefficients;
• inverse-transform means for receiving and transforming the set of frequency-domain video coefficients into a first set of pixel values;
• averaging filter means for receiving the first set of pixel values and transforming selected ones of the pixel values in the first set of pixel values into averaged pixel values to provide a second set of pixel values including the averaged pixel values;
• and
• decimating means for deleting selected ones of the pixel values in the second set of pixel values to provide the low resolution video signal.