[loganross]

There is a lot of talk about anamorphic DVDs and aspect ratios.


Do I lose information when I use ATI DVD Player 7.1 running on a 1024x768 desktop to an LT150 projector (vga)?


If I do, can someone explain? Also what can I do to maintain the maximum amount of info while keeping true to the film as originally formated?



Does it help to run in a window rather than full screen and if so then how do I hide the parts of the desktop outside the video window?


I have found several threads regarding this but I am having a hard time coming to a conclusion.


Thanks

 

[loganross]

still hoping for some help.


Why do so many people not run in full screen mode and instead run in a maximized window mode?

 

[RyanDinan]

If your projector doesn't have a 16x9 mode or an anamorphic lens, then you're losing resolution from and/or altering the orignal anamorphic transfer. Here's why.


In order for your projector to output a correctly proportioned image from an anamorphic transfer, two things have to happen (and not necessarily in this order):


1) The aspect ratio of the anamorphic image (16x9) must be converted to 4x3, which requires the loss of lines of resolution. 25% of the lines (1 out of every 4) are discarded and then replaced by black bars above and below the image to fill the space.


2) The image must be scaled from 720x480 to your projectors resolution (1024x768), which requires interpolating. Since this operation is normally done last, you're interpolating from an image with less detail than the anamorphic image on the disc.


If your projector doesn't have a true 16x9 mode (if it's LCD, it doesnt), then you're going to have to get an anamorphic lens. This will allow you to output the anamorphic image without removing detail, and optically squeeze or stretch the image to the correct proportion.


-Ryan Dinan

 

[Aaron Giles]

Quote:

If your projector doesn't have a 16x9 mode or an anamorphic lens, then you're losing resolution from and/or altering the orignal anamorphic transfer. Here's why.

Actually, as long as you have an XGA or better projector, you will not lose any information with any of the major software DVD players. These players do not 'remove every 4th line' from the source material -- that's absurd. If that were the case, nobody here would be claiming the huge gains in PQ as a result of using an HTPC over a standalone player.


Rather, they take the anamorphically-encoded image (which is 720x480) and use your video card's scaler to scale that to the final 16:9 resolution. For an XGA projector, that translates to a 1024x576 image. Since 1024 is greather than 768, and since 576 is greater than 480, you aren't losing any detail. In fact, as long as the final 16:9 resolution that the image is displayed in has at least 480 lines of resolution, you'll see all the bits that were encoded on the DVD. Higher resolutions will help smooth out scaling artifacts, but they won't add any more resolution to the source.


The advantage to using an anamorphic lens is simply that the DVD player will scale the image from 720x480 to the full 1024x768, and the anamorphic lens will squish that back into the proper 16:9 ratio. Resolution-wise, you're gaining a little bit with an anamorphic lens, but don't think that you need to invest in a $1000+ piece of equipment just to get the advantage of anamorphic DVDs! (Of course, there are other, more significant, advantages to anamorphic lenses -- see the other threads for more info.)


Aaron

 

[JKohn]

I agree with Aaron, as long as you're running at least 1024x768 you shouldn't lose any information from an anamorphic disc. You can verify this by running an anamorphic DVD in a window on your desktop. Note that the aspect ratio of the window is 16:9. The only difference in full screen is that the image will be scaled to the highest resolution your desktop is wide enough to handle, and black bars will be added at the top/bottom.

 

[loganross]

thank you for the replies.



so is there any reason not to use full screen mode?

 

[RyanDinan]

You guys are forgetting that anamorphic transfers are intended to be displayed in a 16x9 aspect ratio. The resolution he's running his monitor at is 4x3. There has to be a conversion so the image appears correctly proportioned.

Software DVD players are normally set to correct for this automatically with the "keep aspect" option, as the developers figure most peopel are going to be watching movies on their 4x3 computer monitor.


Go ahead and turn "keep aspect ratio" OFF in the software, then run the movie full screen on your computer monitor. You'll notice that everything is stretched vertically. This is how it's encoded on the disc. The computer will scale it to whatever resolution you're running - In his case, 1024x768.


If you want it to look correct, original lines of vertical resolution must be removed first. You simply can't keep all the original lines of detail if you have to correct for aspect ratio differences. This is exactly what standalone DVD players do when you tell it you have a 4x3 TV. Whenever it encounters an anamorphic disc, it must downconvert the image to display properly.

At 1024x768, only the inner 576 lines are used for the image. Yes, this is MORE than what DVD is encoded at (480 lines), BUT, the image has been CONVERTED to 4x3 aspect, then scaled to 1024x768. The combination of the aspect conversion and the scaling will introduce artifacts and loss of resolution.


Use your computer monitor to test this:

Go ahead and run an anamorphic DVD full screen on your monitor, while keeping the "keep aspect" option selected.

Take note of how the image looks.


Now,

Turn off the "keep aspect" option in your software DVD player.

Run the movie full screen.

Use the vertical resize control on your monitor to "squeeze" the image down until it's about 16x9.


In the latter method, you're not correcting for the aspect, which preserves the detail better. All that's happening is that the 720x480 image is getting scaled to 1024x768, squeezed in a 16x9 area.


-Ryan Dinan

 

[RyanDinan]

Quote:

Originally posted by JKohn You can verify this by running an anamorphic DVD in a window on your desktop. Note that the aspect ratio of the window is 16:9. The only difference in full screen is that the image will be scaled to the highest resolution your desktop is wide enough to handle, and black bars will be added at the top/bottom.

If you're running a 4x3 resolution on your computer monitor, the only way an anamorphic DVD will appear correctly in a 16x9 window on your desktop, is if you have "keep aspect ratio" selected in your software. This is NOT preserving all the resolution, as it has to convert between the different aspects.


-Ryan

 

[Aaron Giles]

Ryan,


I see your logic, but it is introducing a downconversion that doesn't need to happen, and in fact, doesn't happen.


A non-anamorphic DVD has a resolution of 720x480. It is intended to be displayed on a 4:3 set. If you're running a computer monitor at 1024x768 (which is a 4:3 aspect ratio), then it takes the 720x480 and scales it to fit in a 1024x768 area.


An anamorphic DVD also has a resolution of 720x480. It is intended to be displayed on a 16:9 set. If you're running a computer monitor at 1024x768 (a 4:3 aspect ratio), obviously a 16:9 image doesn't match. So what the software DVD player will do is figure out what's the largest 16:9 area of the current screen mode that I can use? That happens to be a 1024x576 area in the middle of the screen. It then takes the 720x480 and scales it to fit in a 1024x576 area.


There is no downconversion being done. Video cards are capable of scaling horizontally and vertically by different amounts, so it is no sweat to just take the full resolution and scale it to a different output resolution. In this case, downconversion is more work than just using the video card's capabilities to scale it to a 16:9 aspect ratio.


Aaron

 

[RyanDinan]

Aaron,


So you're saying, in your example, that the software is scaling more in the horizontal direction to compensate for the aspect ratio difference? I can see how that would work. I guess I'm too stuck on how standalone DVD players do things....I'm still getting used to the vastly superior picture my HTPC delivers.


Anyway, in that case, a resolution of 800x600 would not retain all the information encoded on a DVD, since the largest 16x9 resolution that would fit, is 800x450. About 30 lines of vertical detail would get thrown away, but 'gain' 80 pixels in the horizontal direction from the scaling. So minmum standard computer 4x3 resolution that resolves all DVD detail is 1024x768, as it allows for 1024x576.


-Ryan

 

[Aaron Giles]

Ryan,


Yes, that's exactly what I'm saying. The scaling done by video cards doesn't have to be the same in both directions ... pretty much all you have to do is tell the video card, "Here's some source data at 720x480, now go scale it to 1024x576" or any other dimension you want.


You're also right about SVGA (800x600) resolution being a bit insufficient to display full resolution from an anamorphic DVD source. XGA or greater seems to be the way to go for a 4:3 projector.


Aaron