Sony FX1: Resolution vs bandwith question at DVinfo.net

Thom Seaman · September 11th, 2004, 02:17 PM

OK so what am I missing here..?

JVC HDV Cams: 1280x720 at 30p requires 19.7Mbps bandwith
Sony FX1: 1440x1080 at 60 requires 25Mbps bandwith

So how does it follow that a 68% increase in image size only requires a 27% increase in data? Does this automatically indicate a more severe rate of compression, and if so is that likely to be noticed? Or is there another variable I'm not taking into account?

Can't wait for the PAL version to hit London - I'm praying for a price cutting war to break out on Tottenham Court Road!

Peace,
Thom

Barry Green · September 11th, 2004, 04:32 PM

The 1440x1080x60i mode has 1.7 times as many pixels per second as the 1280x720x30P mode, but the data rate is 1.3x higher.

So yes, the 1080i mode should be using somewhat more compression. Whether that has any delitirious effect remains to be seen in the footage. Is it possible the field-based compression of 1080i may make it more efficent than the frame-based compression of the 720P? Or maybe 1080i footage WILL show more artifacts, due to the heavier compression... don't know...

David Newman · September 11th, 2004, 06:46 PM

Interlace encoding is typically harder than propressive compression, but putting his aside; as resolution goes up so does image redundancy, so the data rate for the 70% more pixels will not need the same increase in the compressed output. This fact, coupled with reduced noise from 3CCD vs 1CCD, the 25Mbs stream looks very good.

September 11th, 2004, 02:17 PM	#1
Thom Seaman New Boot Join Date: Jan 2004 Location: London, UK Posts: 21	Sony FX1: Resolution vs bandwith question OK so what am I missing here..? JVC HDV Cams: 1280x720 at 30p requires 19.7Mbps bandwith Sony FX1: 1440x1080 at 60 requires 25Mbps bandwith So how does it follow that a 68% increase in image size only requires a 27% increase in data? Does this automatically indicate a more severe rate of compression, and if so is that likely to be noticed? Or is there another variable I'm not taking into account? Can't wait for the PAL version to hit London - I'm praying for a price cutting war to break out on Tottenham Court Road! Peace, Thom

September 11th, 2004, 06:46 PM	#3
David Newman CTO, CineForm Inc. Join Date: Jul 2003 Location: Cardiff-by-the-Sea, California Posts: 8,095	Interlace encoding is typically harder than propressive compression, but putting his aside; as resolution goes up so does image redundancy, so the data rate for the 70% more pixels will not need the same increase in the compressed output. This fact, coupled with reduced noise from 3CCD vs 1CCD, the 25Mbs stream looks very good. __________________ David Newman -- web: www.gopro.com blog: cineform.blogspot.com -- twitter: twitter.com/David_Newman

September 11th, 2004, 04:32 PM	#2
Barry Green Barry Wan Kenobi Join Date: Jul 2003 Location: North Carolina Posts: 3,863	The 1440x1080x60i mode has 1.7 times as many pixels per second as the 1280x720x30P mode, but the data rate is 1.3x higher. So yes, the 1080i mode should be using somewhat more compression. Whether that has any delitirious effect remains to be seen in the footage. Is it possible the field-based compression of 1080i may make it more efficent than the frame-based compression of the 720P? Or maybe 1080i footage WILL show more artifacts, due to the heavier compression... don't know...