Math lesson: Aspect ratios.

Posted on May 9, 2007

I’m writing this to hopefully eliminate any problems that others may have, and possibly enlighten some of you that aren’t aware of something you can do to improve DVD quality. The first thing to cover are aspect ratios. This short was rendered at 1920×820. That equates to an aspect ratio of roughly 2.35:1 (1920/820=2.341). Typical widescreen televisions have an aspect ratio of 1.78 (1920/1080=1.777). In order to get my short to properly fit on widescreen without any stretching, I added 130 lines of black on the top and 130 on the bottom of my frame (130*2=260 + 820 = 1080). This new letterboxed image now has an aspect ratio of 1.78.

Now, in order to take the most advantage of the 720×480 DVD resolution, the newly adjusted short res of 1920×1080 was scaled down to 720×480. This changes the aspect ratio to 1.5. In other words, the image now looks squeezed horizontally. This is what you want. When you encode your MPEG2, you simply set the aspect ratio flag to 16:9. This will tell the DVD player to stretch the image horizontally to give the proper 1.78 (or 16:9) aspect ratio on a widescreen TV. On an old fashioned 4:3 TV, it will add black above and below the image for letterbox output.

Simple enough. The reason you should do it this way is because you are taking advantage of the 480 lines that DVD allows. If you simply add more black on the top and bottom of the screen getting the right aspect ratio, then scale down the image to 720×480 without squeezing horizontally and ignore the 16:9 flag in your encoding software, the real resolution of your image is only 720×306. Doing it that way doesn’t take advantage of all the available lines.


Filed Under TDDUP-Production Log

Comments

Leave a Reply




CAPTCHA image