Reducing Noise by Downsampling? at DVinfo.net

Brian Klug · October 10th, 2004, 06:07 PM

My theory: If I have a 100x100 pixel movie - and it has lots of noise - I can resize it to 25x25, and remove noise at the same time. This is because 16 source pixels = 1 pixel on the final cut, and this 1 pixel is an average of the 16 noisy ones. Therefore a much better signal.

Am I correct? I have DV footage (shot in frame mode) that looks noisy, and I don't mind reducing the size of the movie to enhance it.

Yet simply changing the output resolution in premiere doesn't seem to cut it.

Rob Lohman · October 11th, 2004, 02:30 AM

Your theory is sound in theory. However it largely depends on
how the downsample is done. See if you can change the way
Premiere does the downsample. It might just drop columns and
lines instead of averaging them out.

Andre De Clercq · October 11th, 2004, 03:44 AM

If straight downsampling is performed, not only there will be no noise reduction, but also extra aliasing effects will be introduced if the original (yr 100x100) was sampled at near Nyquist limit. Most decimators used for downsampling use FIR or IIR lowpass filtering before downsampling. Whether noise will be significantly reduced if further dependend on the original noise "spectrum"

October 10th, 2004, 06:07 PM	#1
Brian Klug New Boot Join Date: Nov 2003 Location: Maryland Posts: 7	Reducing Noise by Downsampling? My theory: If I have a 100x100 pixel movie - and it has lots of noise - I can resize it to 25x25, and remove noise at the same time. This is because 16 source pixels = 1 pixel on the final cut, and this 1 pixel is an average of the 16 noisy ones. Therefore a much better signal. Am I correct? I have DV footage (shot in frame mode) that looks noisy, and I don't mind reducing the size of the movie to enhance it. Yet simply changing the output resolution in premiere doesn't seem to cut it.

October 11th, 2004, 02:30 AM	#2
Rob Lohman RED Code Chef Join Date: Oct 2001 Location: Holland Posts: 12,514	Your theory is sound in theory. However it largely depends on how the downsample is done. See if you can change the way Premiere does the downsample. It might just drop columns and lines instead of averaging them out. __________________ Rob Lohman, visuar@iname.com DV Info Wrangler & RED Code Chef Join the DV Challenge \| Lady X Search DVinfo.net for quick answers \| Buy from the best: DVinfo.net sponsors

October 11th, 2004, 03:44 AM	#3
Andre De Clercq Major Player Join Date: Sep 2002 Location: Belgium Posts: 804	If straight downsampling is performed, not only there will be no noise reduction, but also extra aliasing effects will be introduced if the original (yr 100x100) was sampled at near Nyquist limit. Most decimators used for downsampling use FIR or IIR lowpass filtering before downsampling. Whether noise will be significantly reduced if further dependend on the original noise "spectrum"