Why does rendering result in a slightly cropped image?

Post by **jparnold** » Fri Feb 09, 2007 3:24 am

I have noticed that when a DVD is burnt from a project and then shown either on a CTR TV or flat panel (lcd or plasma) all the original picture is cropped - that not all of the original picture is seen.
I realise that this is why there is a "title safe" area when editing.
Actually from what I have observed that amount 'lost' is around half the width of the are OUTSIDE the title safe area.
The original image is 1024 x 576 (PAL 16:9) and the output video also appears to be1024 x 576. It seeems that during rendering the image is a slightly zoomed in image.
Why is this small amount of original image lost during rendering?

daniel · Post by **daniel** » Fri Feb 09, 2007 12:44 pm

I'll make a few assumptions here (to assume is...)

First one since it's 1024*576 I think your ratio is 16:9, not 4:3

Second one: by CTR you mean CRT (Cathode Ray tube) or traditional TV.
In this case the four borders are lost due to the manufacturer of the TV using the overscan area (of Safe Title by Ulead) to hide the barrelling effect of the sphere-section that the tube is. Nothing you can do.

BUT: this does not apply to LCD/plasma screens..
So my guess is either you made a mistake in the square/non square pixels setting, or in the image attributes (keep original ratio vs. use projects size).

As often, it's either that or "something completely different", and then you need to refer to the early Monty Pythons.

Post by **jparnold** » Fri Feb 09, 2007 12:53 pm

Daniel,
Yes I am using 16:9 aspect ratio and a typo resukted in CTR instead of CRT.

I AM using a plasma flat panel and have created a very short video with text characters all over the image (so that I could detect what was lost and what wasn't) in the preview window both INSIDE and OUTSIDE the title safe area and have PROVED (with my Panasonic plasma panel) that some of the image seen in the preview window IS lost (but not everything outside the title safe area).

Trevor Andrew · Post by **Trevor Andrew** » Fri Feb 09, 2007 3:06 pm

Hi John

When you say you are using 16:9 is this the video file (dvd) or the TV settings.

Check the aspect ratio that your TV is set to.

There are several options from Auto, 16:9, 4:3 etc The zoom option the most likely culprit. If I choose the wrong one I loose some of the frame.

If you set 4:3 then you should see full frame but squashed horizontally. Black bars left and right, but you should see all the titles. This shows that the dvd contains the true info.

I have used 16:9 widescreen for quite a while and have no problems. My last slide show displayed the full image. Cannot say what it would be like on a normal TV.

Trevor

Post by **jparnold** » Fri Feb 09, 2007 11:02 pm

Trevor,

With respect I have the TV aspect ratio set to 16:9 which according to the manual "will display a true 16:9 (anamorphic) picture with no aspect distortions. It is NOT set to ZOOM.
There are NO settings for aspect ratio on the DVD recorder/player EXCEPT for RECORDING to DVD (which is 16:9 or 4:3 and mine is set to 16:9). Regardless of that the DVD I used was recorded with the DVD burner in my PC.

You seem to be saying that plasma/lcd TVs do not loose any picture like CRT TVs do.

I still maintain it is something to do with VS and/or the rendering as I have recorded a show on TV, imported into VS and burnt a DVD. The DVD rendered/recorded with VS displays on my plasma TV slightly cropped whereas the original DVD recorded shows the original full picture on the SAME TV.

What is your suggestion now!

IT seems clear cut to me that it is in the encoding performed by VS!

But why? To allow for showing on CRT TV's which display using overscan? If so why isn't there a setting within VS so the user has the option?

Trevor Andrew · Post by **Trevor Andrew** » Sat Feb 10, 2007 11:16 am

Hi John

Just staying with the tv,s aspect ratio, for one more question.

Not all widescreen TV¡¦s have a 16 9 screen.
Some are wider than others, Home cinema type systems comes to mind.

I have a Samsung, the screen measures 71 x 40 cm. this is 16:9 aspect.
The dvd slide show made using VS 10 shows in full, there is no overscan that is noticeable to me.

If I viewed a 16:9 on a wider screen then I would expect to see the conditions you describe.

What are the measurements of your screen???????

I will do some further tests/checks on the videos I produce.
Maybe place a 20px border around the images, then create a slide show.
If i can view the border then i an loosing nothing.

Regards

Trevor

Post by **jparnold** » Sat Feb 10, 2007 12:38 pm

Trevor,

Firstly the image is cropped around the same amount vertically AND horizontally (if the screen was not a true 16:9 then the cropping would be more vertically than horizontally (or vice versus).

Secondly my screen is 920 X 518 (according to my tape measure) which is almost exactly 16:9 (within 0.5mm which is probably due to my inaccurate measurement).

Below is a screen shot of how I proved the partial loss of image after burning to DVD. Note how I have added text above and below the top line of the title safe area as well as numbers to the far left and right sides of the image (both inside and outside the title safe area).

I have superimposed on the screen shot a yellow coloured box which approximates the area of the picture which is displayed on my plasma TV when playing the DVD burnt using VS.

I challenge you to create a short video using VS with similar/same text in the same places and view on your TV and tell me if you can see EVERY character.

2

Trevor Andrew · Post by **Trevor Andrew** » Mon Feb 12, 2007 11:08 am

Hi John

I created a widescreen slide show using 1024 x 576 images.
The images had a 10 pixel border so I could identify the edges when playing the dvd.

Video Studio created the dvd accurately, all details of the images were burned to disc.

Playing the dvd on the PC using Windows Media Player showed the full content including the border.

Playing on my TV was another matter.
The border could not be seen and more of the frame was also lost.

I took a photo of the TV screen and compared the result with the original image.
Using ¡¥photoshop¡¦ I could identify the lost portions of the image.
This was about 30 pixels top and bottom.
30 pixels is not a lot when viewing an image 576 px high. About 5%

Video Studio for me, has not cropped any portion of the original image.
What has been lost is in the viewing of the dvd on my tv.
We cannot compare tv like for like, each tv may produce a different view.

As I came to post this reply I noticed your image in the above post. I will look into this a little further, but I am convinced that it is a viewing problem not a production one.

Can you view your disc using windows media player?

Regards

Trevor

Post by **jparnold** » Mon Feb 12, 2007 12:43 pm

Trevor,

Yes when I play the movie using Windows media player I can see ALL of the original.

It is when viewed on a TV I loose some of the top, bottom and sides and I wonder why with modern flat panel technology. I can understand it with CRT TVs as for a start older TV screens don't have completely square corners but cannot u7nderstand it with flat panels which have square corners.

Thanks for your replies.

sjj1805 · Post by **sjj1805** » Tue Feb 13, 2007 1:45 am

I have recently bought one of those flat screen TV sets that can also double up as a computer monitor. When I get the time I will have to do some tests relating to the 'overscan area.'

What does spring to mind though is that if you are providing copies of your DVD disc to others you must assume that they are viewing on a traditional cathode ray tube television set. Even if your new flat screen monster displays the entire video, your friends/relatives/customers TV sets may not.

You would therefore still need to take the overscan into account even if it isn't an issue with your own set.