Different resizing/aspect ratio scenario

[kevinm]

I have read many discussions about aspect ratio and many guides on the web but these seem to be concerned with the situation where the source aspect ratio is such that the height is less that the display aspect ratio, I think my situation is a little different:

For my situation the source height (576) is greater than the display height (480), also I have to crop some 'noise bars' from the image and I am not sure how to do this without messing up the aspect ratio.


Scenario:

Source: Analogue capture from PAL Hi-8 camcorder, captured at 704x576. Has 'noise bars' on the left (16 pixels), bottom (16 pix) and right (8 pix) of the image.

Destination: NTSC DVD

Display device: Regular NTSC TV (4:3)

The SAR is 1.2222
The DAR is 1.3333 (4:3)


The first question is, when cropping is it critical to maintain the same aspect ratio as the original?

If YES, then I have figured out that the following cropping will keep the same AR as the original ..

left=16
bottom=16
right=8
top=4

(704-16-8)/(576-16-4)=680/556= 1.223


Cropping to the above I see that the noise bars are removed but do I need to do any addborders/letterboxing? I assume not, since my source height (556) is greater than the display height (480).

So, to do the cropping and resizing would the following be the correct approach? ...

Left_crop = 16
Right_crop = 8
Top_crop = 4
Bottom_crop = 16

Crop(Left_crop,Top_crop,-(Right_crop),-(Bottom_crop)).LanczosResize(720,480)


I have used the above but I don't know if it is my imagination but the image played from the DVD onto my TV doesn't look quite right. Am I missing something?


thanks,

Kevin

[mg262]

I don't know much about this... but I think that when you apply the final resize from 704x576 to 720x480, you will be changing the aspect ratio by a factor of (704/720)/(576/480) = 0.814 . But 1.22222/1.3333333 = 0.917 is the factor you want. (Like I said, I'm new to this so I don't know whether those are factors to multiply or divide by... but it doesn't make a difference to the argument above.)

I think this should have everything you want:

http://www.doom9.org/index.html?/capture/par.html

it deals with all cases I can conceive of.

[kevinm]

mg262,
thanks for the pointer to that guide, I had come across others on this site but not that one for some reason.
Yes, it appears to cover my scenario, 'all' I need to do now if figure out what capture chip I have on my MSI VIVO board, I am thinking at the moment that since it is mated with an Nvidia MX440 it is probably a SAA7108 but I am not sure. The manufacturer doesn't admit in the manual to what is on the board, better open up my case and see if the part number is visible.

Kevin

[mg262]

Yes, it appears to cover my scenario, 'all' I need to do now if figure out what capture chip I have on my MSI VIVO board,That's really something for the Capturing forum! Although I've found Google quite effective for this kind of thing in the past. For what it's worth, my MSI TV@nywhere has a Conexant CX23881 in.

[SeeMoreDigital]

It's a shame you can't get your hands on one of Sony's Digital 8 camcorders that offers "on-the-fly" conversion of analogue "8 and Hi8" to digital, and passes the signal down an FireWire cable to your PC.


Cheers

[kevinm]

yeh that would be nice. I used to live in the UK (hence why I have a PAL Hi-8 camcorder), I did try passing the PAL video through my Canon NTSC DV camcorder but it wouldn't sync (it was a bit of a long shot).

I have found some references on the web suggesting that my MSI card uses a Philips SAA-7114H capture device, but the guides referenced from Doom9 only give capture windows for two other SAA 7xxx devices, not the one I am using.

I will open up the case of my computer and try to confirm what my VIVO card uses. Maybe then I can look at the Philips datasheet and figure it out, although I think the 7114 have scalars so I am not sure if I also need to factor in the effects of the (WDM) driver.

I read one article explaining how to use a DVD and test video to determine capture window but I don't have a PAL DVD player to input to my capture card. I suppose I could just ask the manufacturer of my card (MSI) but I don't hold out much hope of getting a reply, especially as this card is now obsolete,

Oh-hum, what fun this capturing/resizing stuff is turning out to be,

Kevin

[kevinm]

mg262,
you are right, this have moved from being a question about resizing to being about capturing. I have moved this discussion to the capture forum, I won't be posting to both so I don't think this consititutes cross-posting,

thank to everyone for their help,

Kevin

[Wilbert]

I have found some references on the web suggesting that my MSI card uses a Philips SAA-7114H capture device
If Canada is also NTSC, then it's probably the same as the SAA-7113 one. Thus cap window of 53.33 µs (section 5). If you want to know for sure you can determine the active capture window yourself:

http://www.doom9.org/index.html?/capture/capture_window.html

[kevinm]

Hi Wilbert,

yes Canada is NTSC but my dilema is that I am capturing PAL video here.

If I read that guide correctly I need a DVD player to output analogue video into my cature card, then analyze the capture to determine the window.

I don't have a PAL DVD player, and my NTSC DVD player won't play PAL disks.

So, effectively I don't have a reference with which to perform the analysis,

Kevin

[Arachnotron]

If Canada is also NTSC, then it's probably the same as the SAA-7113 one. Thus cap window of 53.33 µs (section 5). If you want to know for sure you can determine the active capture window yourself:The SAA7113 is a ITU chip without scaler that is often found on cheap USB capture devices without hardware compression.
The SAA7114 however is more like the 713x series in that it has the full set of scalers. The difference with the 713x is that the 713x series is more geared towards TV cards and decoding TV stereo sound, while the SAA7114 is used for "pure" video decoding like ViVo cards and cheap TBC's.

So my guess would be that the 7114 will be closer to the 7134 drivers as far as capture window settings goes. But in the end it depends on wat is set in the driver.