Resolution Loss

Frank Vrionis · March 21st, 2005, 09:51 AM

Maheel, tell me it's not true! I'm losing more lines?

Can't i play a PAL AVI thru a computer to a projector and get the full resolution?

Or DVD to a projector using a DVI cable or something?

Luis Caffesse · March 21st, 2005, 09:57 AM

Frank,

What Maheel is saying is that it is a limitation of the DV format.
Meaning, if your PAL video was shot on DV, you are limited to what the DV format can record (which is 500 lines).

So, even if you were to play it back through a computer to a projector you would only get the resolution that was orignally recorded to tape.

To get around this limitation you would have to take DV out of the equation completely.

Jamie Abbott · March 21st, 2005, 11:46 PM

There seems to be some confusion here regarding resolution. While it is true that DV/DVCam is limited to around 500 lines of resolution (I think it is 525 for NTSC, 625 for PAL) this refers to number of scan lines.

The 720x480 (NTSC) and 720x576 (PAL) refers to non-square pixels (horizontal x vertical) giving a 4:3 image. This is why PAL has better resolution than NTSC, i.e. more pixels. (Let's not get into the 4:2:0 vs. 4:1:1 color debate.)

For what it's worth, a cropped 16:9 DV-NTSC image is 720x406 (if I remember right), so you lose some vertical resolution. Use a Century anamorphic adapter on a PAL camera and you'll gain almost a third in vertical resolution, as it maintains the 576 vertical pixel count.

Does this help?

Frank Vrionis · March 22nd, 2005, 02:48 AM

Jamie thanks. It does help enormously. Now it has opened all sorts of questions.

Never new the pixel count and resolution were different.

<<Use a Century anamorphic adapter on a PAL camera and you'll gain almost a third in vertical resolution, as it maintains the 576 vertical pixel count.>>

Are these real lines or pseudo?

Juan's got this image form his camera:
http://www.reel-stream.com/capture/36bit_HD_sm.jpg
the resolution is 1124x720

....I don't know what my question is but I’m getting there.

Jamie Abbott · March 22nd, 2005, 07:06 AM

Don't misunderstand. These are different ways of measuring resolution.

This page --> http://members.aol.com/ajaynejr/vidres.htm

provides a darn good basic explanation of resolution variables, much better than I could do. (Better yet, read Scott Billup's book DIGITAL MOVIEMAKING.)

The Century or Panasonic anamorphic adapters "squeeze" the image to utilize the full range of a 4:3 chip to produce 16:9 images. These are "real" lines, if I get your meaning.

The near-HD 1124x720 images on the Reel Stream site are impressive, but they are captured without the compression that is performed in-camera with DV. So they are uncompressed high-resolution images.

Graeme Nattress · March 22nd, 2005, 07:17 AM

<<<-- Originally posted by Jamie Abbott : There seems to be some confusion here regarding resolution. While it is true that DV/DVCam is limited to around 500 lines of resolution (I think it is 525 for NTSC, 625 for PAL) this refers to number of scan lines.
-->>>

When people quote "lines of resolution" they're referring to vertical lines which means horizontal resolution. Although both NTSC and PAL standard def formats have 720 horizontal pixels, if you actually allowed such a detailed image to be recorded, you'd get aliassing artifacts, hence the horizontal resolution is limited by the lens, by filters etc. to around 500 lines. Although 720 pixels are recorded, think of it recording a slightly blurred image, and hence the resolution of the system is limited. All cameras do this, and it's quite necessary to avoid artifacting. Basically, think of it the other way, we record with more pixels than we need to make sure that the underlying resolution is recorded accurately.

Now to 525 and 625. These are the horizontal line counts for NTSC and PAL, and are total lines, not picture lines. The lines used for picture are 480 (or 486) and 576 respectively and equate to vertical resolution. However, just like horizontal resolution, this is number of pixels, not underlying resolution of the reproduced image, which will be lower, again to stop aliassing and line twitter on interlaced systems.

Graeme

Andre De Clercq · March 22nd, 2005, 07:47 AM

Horizontal resolution in TV is expressed in terms of vertical lines (black lines +white lines, not line pairs!) measured on length which equals the picture hight. So in a 720x480 (4:3) image the max system resolution is 720x3/4=540 TVL/ph (TV lines per pixel hight). For several reasons this limit is never being reached .

Rob Lohman · March 23rd, 2005, 05:09 AM

Thanks for that tech explenation Andre!

Frank Vrionis · March 23rd, 2005, 05:26 PM

thanks for that guys. i'm getting there.

March 21st, 2005, 09:57 AM	#17
Luis Caffesse Major Player Join Date: Apr 2004 Location: Austin, Texas Posts: 704	Frank, What Maheel is saying is that it is a limitation of the DV format. Meaning, if your PAL video was shot on DV, you are limited to what the DV format can record (which is 500 lines). So, even if you were to play it back through a computer to a projector you would only get the resolution that was orignally recorded to tape. To get around this limitation you would have to take DV out of the equation completely. __________________ Luis Caffesse Pitch Productions Austin, Texas

March 22nd, 2005, 07:17 AM	#21
Graeme Nattress RED Problem Solver Join Date: Sep 2003 Location: Ottawa, Canada Posts: 1,365	<<<-- Originally posted by Jamie Abbott : There seems to be some confusion here regarding resolution. While it is true that DV/DVCam is limited to around 500 lines of resolution (I think it is 525 for NTSC, 625 for PAL) this refers to number of scan lines. -->>> When people quote "lines of resolution" they're referring to vertical lines which means horizontal resolution. Although both NTSC and PAL standard def formats have 720 horizontal pixels, if you actually allowed such a detailed image to be recorded, you'd get aliassing artifacts, hence the horizontal resolution is limited by the lens, by filters etc. to around 500 lines. Although 720 pixels are recorded, think of it recording a slightly blurred image, and hence the resolution of the system is limited. All cameras do this, and it's quite necessary to avoid artifacting. Basically, think of it the other way, we record with more pixels than we need to make sure that the underlying resolution is recorded accurately. Now to 525 and 625. These are the horizontal line counts for NTSC and PAL, and are total lines, not picture lines. The lines used for picture are 480 (or 486) and 576 respectively and equate to vertical resolution. However, just like horizontal resolution, this is number of pixels, not underlying resolution of the reproduced image, which will be lower, again to stop aliassing and line twitter on interlaced systems. Graeme __________________ www.nattress.com - filters for FCP

March 23rd, 2005, 05:09 AM	#23
Rob Lohman RED Code Chef Join Date: Oct 2001 Location: Holland Posts: 12,514	Thanks for that tech explenation Andre! __________________ 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

March 21st, 2005, 09:51 AM	#16
Frank Vrionis Regular Crew Join Date: Feb 2005 Posts: 93	Maheel, tell me it's not true! I'm losing more lines? Can't i play a PAL AVI thru a computer to a projector and get the full resolution? Or DVD to a projector using a DVI cable or something?

March 21st, 2005, 11:46 PM	#18
Jamie Abbott Tourist Join Date: Mar 2005 Location: Tallahassee, FL, USA Posts: 2	There seems to be some confusion here regarding resolution. While it is true that DV/DVCam is limited to around 500 lines of resolution (I think it is 525 for NTSC, 625 for PAL) this refers to number of scan lines. The 720x480 (NTSC) and 720x576 (PAL) refers to non-square pixels (horizontal x vertical) giving a 4:3 image. This is why PAL has better resolution than NTSC, i.e. more pixels. (Let's not get into the 4:2:0 vs. 4:1:1 color debate.) For what it's worth, a cropped 16:9 DV-NTSC image is 720x406 (if I remember right), so you lose some vertical resolution. Use a Century anamorphic adapter on a PAL camera and you'll gain almost a third in vertical resolution, as it maintains the 576 vertical pixel count. Does this help?

March 22nd, 2005, 02:48 AM	#19
Frank Vrionis Regular Crew Join Date: Feb 2005 Posts: 93	Jamie thanks. It does help enormously. Now it has opened all sorts of questions. Never new the pixel count and resolution were different. <<Use a Century anamorphic adapter on a PAL camera and you'll gain almost a third in vertical resolution, as it maintains the 576 vertical pixel count.>> Are these real lines or pseudo? Juan's got this image form his camera: http://www.reel-stream.com/capture/36bit_HD_sm.jpg the resolution is 1124x720 ....I don't know what my question is but I’m getting there.

March 22nd, 2005, 07:06 AM	#20
Jamie Abbott Tourist Join Date: Mar 2005 Location: Tallahassee, FL, USA Posts: 2	Don't misunderstand. These are different ways of measuring resolution. This page --> http://members.aol.com/ajaynejr/vidres.htm provides a darn good basic explanation of resolution variables, much better than I could do. (Better yet, read Scott Billup's book DIGITAL MOVIEMAKING.) The Century or Panasonic anamorphic adapters "squeeze" the image to utilize the full range of a 4:3 chip to produce 16:9 images. These are "real" lines, if I get your meaning. The near-HD 1124x720 images on the Reel Stream site are impressive, but they are captured without the compression that is performed in-camera with DV. So they are uncompressed high-resolution images.

March 22nd, 2005, 07:47 AM	#22
Andre De Clercq Major Player Join Date: Sep 2002 Location: Belgium Posts: 804	Horizontal resolution in TV is expressed in terms of vertical lines (black lines +white lines, not line pairs!) measured on length which equals the picture hight. So in a 720x480 (4:3) image the max system resolution is 720x3/4=540 TVL/ph (TV lines per pixel hight). For several reasons this limit is never being reached .

March 23rd, 2005, 05:26 PM	#24
Frank Vrionis Regular Crew Join Date: Feb 2005 Posts: 93	thanks for that guys. i'm getting there.