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-   -   a couple of newbie q's (https://www.dvinfo.net/forum/general-hd-720-1080-acquisition/44628-couple-newbie-qs.html)

David Downes May 15th, 2005 07:27 PM

a couple of newbie q's
 
Please excuse the newbie questions regarding 1080i on the Sony FX1/Z1E. Firstly, if you shoot 50i with the shutter speed at 25, arent you essentially shooting progressive frames?

Secondly, I keep reading about 1080i being a resolution of 1920 x 1080 pixels but isnt it true that the actual number of horizontal captured pixels is 1440, each pixel being 'stretched' to fill a 1920 (square) pixel frame width? Can someone tell me why non square pixels are better (or worse) than square ones?

Douglas Spotted Eagle May 15th, 2005 08:26 PM

Quote:

Originally Posted by David Downes
Please excuse the newbie questions regarding 1080i on the Sony FX1/Z1E. Firstly, if you shoot 50i with the shutter speed at 25, arent you essentially shooting progressive frames?

Secondly, I keep reading about 1080i being a resolution of 1920 x 1080 pixels but isnt it true that the actual number of horizontal captured pixels is 1440, each pixel being 'stretched' to fill a 1920 (square) pixel frame width? Can someone tell me why non square pixels are better (or worse) than square ones?

No, you're not shooting at 1080p, because the Z1 image is always interlaced in HDV mode.
Stretched pixels or square pixels is not really an issue. The real issue lies in how the pixels are generated. DV also uses a stretched/non-square pixel aspect ratio. The concern that some folks have with HDV is the compression coupled with the non-square pixel issue.

Tommy James May 15th, 2005 08:55 PM

Electronically the image may be interlaced but for all pratical purposes shouldnt shooting in cf30 produce progressive like images?

Jack Zhang May 15th, 2005 09:21 PM

Quote:

Originally Posted by Tommy James
shouldnt shooting in cf30 produce progressive like images?

No, CF30 is "field doubling," it's still interlaced, it's way better to shoot interlaced footage then de-interlace and interpolate feilds on your PC/Mac. you can watch some CF30 footage and see for yourself below: (in the de-interlacing panel of VLC, choose Bob to see the footage at 60 fields)

Andrew J Hall May 15th, 2005 11:53 PM

My own newbie question, how does the camera shoot 1/25 (or 1/3) second while delivering 50/60i?

Andrew

Ron Evans May 16th, 2005 06:48 AM

In simple terms the CCD's in a camera collect light for the time period defined by the shutter speed( there isn't a real shutter as in a still film camera). The collected data for each pixel is then read out into a buffer that is sampled at either 50 or 60 times a second alternating between odd and even lines to create an interlaced image for recording to tape. When the shutter speed is equal to or faster than the buffer sample rate new data is provided at each sample. If the shutter speed is slower than the sample rate there will be repeat samples. That is, movement in the image will be affected.
This is a simple explanation, it is a little more complicated in practice due to the way CCD's collect light charge and transfer to the read buffer!!.

Ron Evans


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