Monday, June 28, 2010

Okay, this is driving me mad…

Allow me a moment to talk about HD. That's HD as in 'High Definition'. It's amazing how long it's been around and how so few people still understand what 'HD' means.

For example, last night, I was perusing the interwebs when I found a review of my Netbook where the owner complained that it chugged a little when he tried to watch a HD movie.

My question was this: Why in the blue hell would you try to watch a 1080p movie on a 1024x600 screen?

Ok, let me start with a little primer. You know how some HDTVs are 720p and others are 1080p? What that number refers to is the number of horizontal rows of pixels (dots) that make up the picture. A 1080p TV simply has more pixels to make up the picture, so given a constant screen size, a 1080p picture will be sharper and more detailed than a 720p picture.

Think of it this way: Imagine trying to draw a picture on graph paper, but you have to draw the picture by completely filling in the squares on the paper. If you have a large sized piece of paper, and that paper has 720 rows of squares, you won't be able to draw as detailed a picture on that as you would on a same piece of paper with 1080 rows of smaller squares.

Put simply, the more pixels/dots you have, the sharper the image.

However, and this is the part people miss: screen size is a huge factor. It's actually possible to have a sharper picture on a 720p set than it is on a 1080p set.

Okay, most people are at least vaguely aware of the term 'Dots per Inch' or DPI. You know when you print something, if you print a picture at 100 DPI it's not going to be as sharp as if you print at 300DPI. That's common sense. If we go back to our graph paper analogy, if you can fit 300 dots in an inch, it's going to make up a sharper image than if you can only fit 100 dots in an inch.

So let's imagine you have a huge-ass 50" 1080p HDTV with a screen that's around three feet tall. With those 1080 rows of pixels spread over three feet, that's 30 pixels per inch. For all intents and purposes you have a '30 DPI TV'.

Now imagine you have a smaller 720p TV with a screen that's only a foot tall. When you divide those 720 rows over a single foot, that works out to 60 pixels per inch, meaning you have a 60 DPI TV, which means even though there aren't as many pixels, the picture is going to appear twice as sharp as the big 1080p TV.

In fact, that was the whole point of HD. Screens were getting bigger, and when you stretch a standard definition picture (320p) across a fifty inch screen, it looked like crap. As screens got bigger, the number of pixels per inch fell, so you needed the higher resolution to just to keep the original picture quality. Basically, you need a 1080p screen just so the picture on a big 50 inch screen will look as good as a standard definition picture will look on an old 20" screen.

The easiest way to understand this is to go watch a youtube video and see just how much the picture quality falls between watching it in a widow and watching it full screen. There's the same number of pixels making up the movie in both cases, but in full screen mode, those pixels are having to stretch over a much larger space. The number of pixels isn't nearly as important to picture quality as pixel density is…the number of pixels per inch.

So back to the guy complaining about a 10" netbook not being able to show Hi-Def video without chugging…there's no point. You're watching a 1080p video downsized to 600p…and that 1080p video isn't going to look any sharper on the netbook screen than a video that's 'natively' 600p.

Basically, the netbook screen is only 5" tall, meaning that at its max resolution of 600p, the screen has a resolution of 120 pixels per inch. When you compare this to even a smaller 32" 1080p screen, which is approximately 16" tall…that works out at 67 pixels per inch, just over half the pixel density, and therefore 'sharpness', of the netbook.

Yes, we like to get hung up in the numbers, and we want a 1080p screen because 1080 is a bigger number than 720…but the math is simple. A 600p movie on a netbook's 10" screen is actually going to be significantly sharper than 1080p movie on a 32" 1080p screen.

Long story short, your netbook doesn't need to be able to run HD movies, because a 600p movie will appear to be just as sharp (and in many cases sharper) on a 10" screen than a 1080p movie will appear on even a 32" screen.

I know that to a lot of people this is blasphemy…but from a picture clarity and quality point of view, that 10" netbook screen is actually higher definition than your 1080p TV set. The higher the number of pixels per inch, the sharper the final image.

No comments: