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High Definition Explained
With the release of the Apple TV, we have seen a lot of confusion over High Definition standards. Benjamin takes the time to break down what all of those numbers, letters, and more numbers mean.
Benjamin Higginbotham with TechnologyEvangelist.com. Here talking today
about high definition video and what are numbers and letters mean?
First let’s start off with difference between progressive and interlaced.
Understanding the difference between progressive video and interlaced video is
key to understanding high definition. Interlaced video is what we have been
using from many many years and is the fundamental technology behind standard
definition. Half the resolution is gone it's virtual, it doesn’t actually
exist. The way that work’s is to spilt every frame into two fields and the
first field is every other line of information, so every even line of
resolution is on the screen and every odd line of resolution is not on the
screen it's black. The second field reverses that where every even line is
black and every odd line actually has all the information on the screen. When
you combine those two fields you give one frame and they flash back and forth
very very quickly. What that means is that at any moment in time you never
have the full resolution available to you. You have only got half the
resolution on the screen. Now it flashes so fast that the human eye cannot
percieve the changes in the field, but what it does to is create something
called interlaced artifacting.
Now, interlaced artifacting is when you are taking something like soccer ball,
and you kick it really quickly across the screen, what ends up happening name,
it smeers, it smudges . You get these weird lines that break though the ball
because half the information is virtual and the set can't actually keep up.
The human eye can percieve these changes. It also makes it extremely
difficult to put interlaced content on a progressive monitor, now most
high definition monitors are progressive. Your plasma monitor is progressive,
your LCD screens are progressive, your DLP screens are progressive. The only
thing that really leaves are CRT monitors.
So want is progressive? Progressive video is where every single monitor
resolution is on the screen all the time. There is no virtual field every
thing is of full frame and that means when you kick that soccer ball across
the field, all of the data is there all time. There is no weird smearing,
there is no interlaced artifacting, none of that. So the picture is pure and
perfect every single time. When you go watch a movie in the movie theater,
that’s progressive. When you watch an HD DVD or blue ray disc on your high
definition television, that’s progressive. Progressive is the best way to get
all of your content on the screen all at the same time. So what is this
matter? Let’s next talk about resolution.
There are two resolutions in high definition video 720 and 1080. Another
progressive and interlaced goes after that, so 720p will be 720 progressive
lines of resolution in other words all of the data is there all the time.1080i
would be 1080 virtual lines of resolution. So 540 actual lines of resolution.
Notice I said 540 actual lines of resolution. Well this is a tricky
interesting area here and that is when you shoot 1080i when you are displaying
1080i, there are actually 1080 lines of resolution on the screen so you get
all that extra detail. But half of them are off at any moment in time. So
if we were to convert that to progressive it's 540 progressive lines of
information. It is not exactly fair comparison because they are flashing so
quickly that the human eye can perceive them, but they are not there, they are
virtual and that’s what creates how bunch of problems. A lot of people thing
that 1080i is a standard above 720p but because of that virtual information,
it’s not, it’s actually quality wise 1080i at the bottom 720p next and
1080p.1080p being 1080 progressive lines of resolution of all of the
resolution out there . Now HD DVD and blue ray they can do 1080p you can
download1080p on the internet but you cannot broadcast 1080p, at least not
today the highest broadcast lines of resolution you can go is 1080 interlaced
lines or 720 progressive lines. So that’s why we say at Technology Evangelist
1080i comes below 720p. If you had your choice I highly recommend doing 720p
before 1080i especially if you have a plasma monitor, an LCD monitor or a
DLP monitor because your display technology is not interlaced. It’s
progressive, there is one more number that comes in to the formula and that’s
the frame rate. Understanding frame rate requires again understanding the
difference between interlaced and progressive. See interlaced is two fields
makes one frame, so they measure the frame rate by fields not frames. So let’s
use 1080i vs 1080p for example.
You will sometimes see 1080i/60 that means 1080 interlaced lines at 60 fields
per second. 1080p/60 is 1080 progressive frames at 60 frames per second. So
interlacing gets you every time. It gets you on interlaced artifacting and it
gets you on the frame rate. Because 1080i/60 is really only 1080p30 and is has
got all that extra interlaced garbage and that makes image look like
poo! So let’s go over the actual HD quality spectrum again. It actually
starts at 1080i and then it goes to 720p and above that is 1080p. Now a lot of
people say, what about 480p? Technically that’s not high definition, that’s
considered enhanced definition. 480i would be standard definition, so the
entire scale looks like 480i being standard definition. 480p, 1080i, 720p and
then 1080p and that’s how the entire high definition spectrum works.
Now lot of people argue with me saying that 1080i belongs above 720p and lot
of people argue my point that belongs below it. You know there is no right
answer. The one thing is 1080p is the ultimate place to be you. That’s were
you really want to be. That’s not a high definition format, higher than that.
It’s all progressive so it's all real. 1080i is an interim format
and with all of the pains, it gives you the interlaced order fact and you have
to increase your bit rate to get a better looking picture and with the frame
rate problems don’t even deal with it. Stay with 720p or 1080p if at all are
possible. So those are your high definition formats, hopefully now you
understand what all the different numbers and letters mean, and what will work
best in your situation.
2. Posted by: Michael on April 26, 2007 5:34 PM:
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Great video! I needed some solid HD background, but never bothered since I'm poor and still watching a 15" TV.
3. Posted by: Joe on April 27, 2007 8:38 AM:
Wow - thanks for breaking it down. I check the site everyday and though ive been working with computers for more than half my lifetime, i always learn something new! Please, keep on it!
4. Posted by: Dale Smith on June 21, 2007 4:05 PM:
This is a somewhat misleading video. 1080i CLEARLY looks cripser and superior to 720p in static or slow moving shots, just as 720p CLEARLY looks smoother and superior to 1080i in fast moving shots. The whole "540" thing is, frankly, silly, because the human eye perceives all 1080 lines AT ONCE, due to persistent vision. And the idea that "your plasma tv is progressive" is also incorrect as a blanket statement, since some plasma TVs are native-progressive (like Sonys) and some plasma TVs are native-interlaced (like Hitachis). So, while I appreciate the information, this definitely needs a little correcting in order to be accurate.
5. Posted by: Benjamin Higginbotham on June 22, 2007 12:57 AM:
Dale, I would respectfully disagree.
In general 1080i does not look crisper, even in slow or static shots. Of course crisp is a subjective element that can be perceived differently by different people (some people like to turn the 'sharpness' up on their CRTs even though it starts to distort the picture) which makes it difficult to discuss. I'm coming at this from a 'what was captures is displayed' approach and not from a 'blow out the whites and blacks to get more contrast' approach. Even with little to no motion, interlacing adds jagged diagonal lines and creates throbbing on high-contrast w/ narrow elements. This can create the illusion of crispness, but in actuality it's image distortion. That's not what it looks like in person, it's not how the director intended it, it's a side effect of interlacing. The higher resolution is nice, but much of it is lost in the interlacing process. My favorite topic is how many people LOVE Discovery channel's 1080i video saying that it 'clearly shows off the clarity of 1080i'. For a while there a lot of their content was shot on a Panasonic Varicam. This is a couple of years ago, they may still be shooting that way, or they may have moved to a different system, I don't know anymore. For those who don't know, the Varicam is a 720p only camera designed to emulate film as best it can, no 1080i modes at all. They took the 720p, scaled it down to 1080i and called it a day. I must agree though, it looks stunning, but the raw 720p looks even better. I believe the primary program at the time was called 'Planet Earth'.
The 'smoother' effect has more to do with framerate than it does with interlaced vs progressive. Right now 720p supports twice as many possible frames as 1080i does. It's deceptive because it's labeled 1080i/60 or 720p/60 which would logically indicate 60 frames in each format, but 720p is frames whereas 1080i is fields or 1/2 of 1 frame meaning 30 frames per second (29.97 to be exact). Why they decided to measure differently is beyond me, it should all be done in frames and not fields, but it is what it is. This is all great, but the frame rate is first set by the content creator and then by the broadcaster. If I shoot a video at 24 frames per second, the smoothness of my video will never improve more than 24. If I shoot at 60 then broadcast at 24 I'm still limited to 24. The smoothness of a video is determined by frame rate. That's part of the reason ESPN went for 720p/60. They can capture at 60fps and then broadcast that same 60 which looks like butter. 1080i can only do 1/2 that and would tear to bits in high-action like that.
The display technology of plasma is progressive. I've not heard of an interlaced plasma other than the scaler in the plasma, but that's just a sub-set of the monitor itself. Unless Hitachi is using something other than a gas matrix display plasmsa element, their front end is progressive with an interlaced scaler. It's completely possible that there's a second plasma technology that I'm not aware of, but if there isn't then it's simply a case of Hitachi getting cheap with the scaler and trying to show off bigger numbers than they really have access to. I would be curious to know what the display matrix of the actual glass can show vs what their scaler can do.
I stand by my assessment that 1080i is a hack job that has no place in the current market. It's a bigger number that marketers are trying to throw out until 1080p is a pricepoint reality. If you're going to buy a camera make sure it does progressive. If you're buying an HDTV make sure it does progressive. Interlaced is nothing but a nightmare that looks like poo no matter what the source.
To date there are only two times in very specific scenarios that I would consider 1080i:
1 - With a CRT display as a CRT will scan lines anyhow, so interlaced makes sense here (and looks great). The problem with CRTs is that they are super heavy and I've yet to find a 50" CRT or larger.
2 - With digital signage. When running something like SCALA on an HD monitor the interlacing can actually help the image become a bit more viewable at a distance for some odd reason. Get close and it throbs and the lines can be too skinny, but general digital signage is good about holding to the ATSC color spectrum and not putting up 1 pixel thick lines. I don't know why, but signage on interlaced monitors actually looks pretty good. Never seen SCALA run on a 1080p set yet as I left the R&D job I used to have before they could get in an industrial 1080p set with a computer powerful enough to drive it. Having said that, signage at 720p looks stunning as well and I have a feeling that signage at 1080p will blow both formats away. Now I really want to go test that...
6. Posted by: Greg on April 4, 2008 3:24 PM:
Awesome article, thanks, just what I was looking for in trying to explain "high def" to somebody who thinks their little 1080i consumer camera isn't any different than high end cameras for resolution (and quality, and audio capabilities, and lens glass, and....)
7. Posted by: Rob on June 2, 2008 12:02 AM:
Ok, so here's my problem/question about your explanation of interlaced vs progressive. I understand progressive completely, I got it. As for interlaced. Your explanation suggests that a CRT set displays images in an interlaced format and that when the upper field is showing, the lower field is actually TURNED OFF. This is where my question/disagreement is. My understanding of interlaced video is that the upper and lower fields are updated every 1/60th of a second alternatingly but that each field is actually shown for 1/30th of a second. So you would be showing fields like this:
1/2, 3/2, 3/4, 5/4, 5/6, 7/6, 7/8, etc. Am I wrong? Is it actually showing 1/black, black/2, 3/black, black/4, etc? Thanks for any clarification.
8. Posted by: Dave on April 14, 2009 7:05 PM:
Posted by: Rob on June 2, 2008 12:02 AM:
you are completely correct. this article is very misleading. As far as can be perceived by the human eye there is just as much information and resolution in 1080i. Interlaced video as stored on digital video tape is of a higher bitrate than progressive, there is actually more information. If you want to create a single still frame from interlaced footage though you will have to either merge the fields or double lines from on field, both processes will result in a blurred and lame looking still.
On artifacts, sport looks way better in interlaced. Noone shoots sport progressive because of the blur factor at slow shutter speeds and judder at higher shutter speeds. Fast motion capured in interlaced looks clearer and smoother.
Movies and drama look better progressive and sport/news look better interlaced. Having said all that, its what you shoot that matters, the display can't change that. I'd make sure to buy a tv capable of displaying 1080p as it is better for watching movies etc.