So what is the difference between 720p and 1080p? What about 1080i vs 1080p?
One of the problems with home cinema technology, is there is a seemingly endless list of acronyms, numbers and technical terms to understand.
For instance, many people buy 1080p televisions without really understanding what it means, and the resolution of high-definition images is an area where people get very confused. They don't realise that understanding these terms a little can help them get the best from their new 1080p TVs.
But don't despair, it's a bit like riding a bike while balancing a fish on your head, it's not that difficult once you get the hang of it.
Let us start by understanding the basic terms.
1080p refers to the resolution of an image that is sent to our TV.
A 1080p resolution can also be called 'Full HD'.
It is also often used to describe a 1080p television that has a widescreen 1920 x 1080 native resolution. However, the true meaning of 1080p refers to the resolution of the image rather than a TV resolution.
Go here for an article on the difference between image and TV resolution.
A 1080p image is a high-definition picture which is created with a
1920 x 1080 resolution..
This means that one frame of the picture has a widescreen aspect ratio, with a resolution of 1,920 pixels of information across (or horizontal), and 1,080 pixels of information down (or vertical). Therefore in total it has over 2 million pixels of detail.
The 'p' at the end of 1080p is also important.
It means that the image has been recorded in progressive scan - which is a better way of creating images than interlaced scan - which is the traditional way of transmitting television images.
Progressive scan produces a better quality of image because the picture is created by drawing each frame of the image in one pass down the screen - from line one to line 1080. This produces a very stable and clear picture.
Progressive scan is also the way that flat screen televisions draw an image - which is another reason why a progressive scan image is better for this type of television.We can only get a true 1080p image from Blu-ray players and some PS3/Xbox games.
A 1080i image is still regarded as high-definition.
As you may be able to guess from the number, the resolution of a 1080i image is the same as 1080p, and it is also a widescreen aspect ratio.
It has the same resolution in pixels as 1080p - so each frame has a horizontal resolution of 1,920 pixels and a vertical resolution of 1080 pixels. Therefore, it can also be called 'Full HD'.
The big difference is in the letter at the end - the 'i'.
This means that a 1080i image is transmitted as an interlaced scan picture, which means each frame of 1080 lines is actually drawn in two passes.
First all the odd lines are drawn - from 1 to 1079. Then all the even lines are drawn - from 2 to 1080. Each of these passes is known as a field - and so two fields (of 540 lines each) make up one frame of 1080 lines.
Therefore, with an interlaced image, it takes slightly longer for our eyes to see a full frame when compared to progressive scan.
So although a TV does this drawing process pretty quickly (50 or 60 times per second depending on where you live in the world), our eyes can often detect this as a slight flicker or unstable image.
This type of image resolution is used commonly used by TV companies when they transmit an 'HD' image - and they use this method because it takes less bandwidth to transmit an interlaced image than a progressive one.
The third type of high-definition image is known as 720p.
It has less pixels compared to a 1080p/i image - but is still classed as high-definition and has a high level of detail.
It has a widescreen aspect ratio with a horizontal resolution of 1280 pixels and a vertical resolution of 720 pixels.
Therefore in total it has 921,600 pixels of information, compared to over two million pixels with 1080i and 1080p images.
As with 1080p, the 'p' at the end indicates it is a progressive scan image which is drawn in one pass down the screen.
Like a 1080i image, this resolution is commonly used by TV companies to transmit an 'HD' picture. It has less pixel information than a 1080i image and so requires less bandwidth to send - but it is transmitted in progressive scan which is an advantage over an interlaced image.
We now have a wide range of input devices to use with our flat screen TVs - Blu-ray players, DVD recorders, cable TV boxes and various forms of digital TV receivers.
The problem is many of these devices often offer a range of output resolutions, and so it can be confusing to know which one to choose.
The best way to approach this issue is to always try to match the resolution of your input signal to the native resolution of your TV.
By doing this you are minimising the amount of processing the TV has to perform - and so in theory you should get the best possible image for the equipment that you have.
However, just to confuse you, there are also circumstances when you may not want to do this.
Let us compare the common high-definition TV resolutions and try and decide which is better to use. I will assume here that we are sending these images to a modern flat screen HDTV.
So what do we go for when we have a choice of 1080i vs 1080p?
Well, in this instance it is always better to go for 1080p.
Your HDTV is a progressive scan device, and so it is better to send it a progressive image. If you send an interlaced image then the TV will have to de-interlace the picture first before it can show it - and this can affect the picture quality.
A native progressive scan picture should appear sharper and 'flicker-free' compared to an interlaced image.
This is true whether you are sending the image to a 1080p television, or a 720p native resolution screen.
This is harder to call, and if you are sitting more than 6 or 7 feet away from your screen, then many people will struggle to tell the difference regardless of the resolution you use.
Obviously 1080p has a higher resolution than 720p and so in most circumstances you would choose this - and you would always choose this resolution for 1080p TVs.
However, bearing in mind our guideline of matching the image resolution and the native resolution, it could be a slight advantage to send a 720p image if you had a 720p (or 768p) screen. This would ensure that the TV doesn't have much scaling to do before showing the image.
However, the results of this can vary between models of television, and could also depend on the quality of the image coming from the source device - so the best idea may be to test both.
If you switch the output of your source between 720p and 1080p, you may notice a difference in picture quality on your 720p TV - or you may not!
If there is no noticeable difference - then who cares which one you choose.
This is an interesting one.
With 720p you have the choice of a lower resolution image (worse) with progressive scan (better) - and with 1080i you have a higher resolution image (better) with interlaced scan (worse).
In theory, both of these has an advantage over the other - and also a disadvantage.
The one you choose may just come down to testing it on your equipment and seeing if you can see a difference.
As already mentioned, as a starting point I would try matching the image and native resolution. Therefore I would suggest 720p for a 720p/768p TV, and 1080i for a 1080p TV.
However, you may find that the stable progressive scan 720p image will look slightly better even on the 1080p screen - as the TV doesn't have to de-interlace the image.
The best results may well come down to the quality of the equipment you are using, and how well the images are scaled and de-interlaced.
Let your eyes be the judge.
Initially it can seem confusing when we see all these technical terms thrown about - and it is something that we see a great deal when we are looking to buy a new TV.
However, once we look into the details, we can see that there isn't much to be scared of.
When it comes down to deciding which resolution to send our TV (assuming we have a choice), then there isn't always a completely black and white answer - there isn't always a 'right' choice.
However, if we are prepared to do a little bit of experimenting - and learn to trust our eyes - then we will get the best results from our equipment. It's a waste to be buying a 1080p television if you don't understand how to get the best picture that you can on the screen.