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23
Dec
posted by - Wednesday, 23 December 2009

hdtvfordummies_working2

I guess you could call this “HD Formats for Dummies”, but if you’ve been reading our blog, you are certainly no dummy. There are so many varieties of HD out there and it can all get a little confusing. My aim here is to help organize the different formats and clear up some common misconceptions. To do this I’ve broken down the HD formats into three categories: Resolution, Frequency, and Frame Rate. With these three parameters, you can come up with any HD signal available. Keep in mind that not all the HD formats we will discuss can be sent for broadcast, so I will also point out those formats and how they effect your final product.


Resolution

This is the easy one because we only have two agreed upon standards for HD broadcast: 1280 pixels x 720 pixels and 1920 pixels x 1080 pixels. These two standards are often just referred to by their vertical resolution only – 720 and 1080. So if you see those number they are just simplifying the otherwise wordy description of the resolution standard.

Beyond these two resolutions we have two higher resolution standards that the DCI (Digitial Cinema Initiatives) has set – “2k” at 2048 x 1024 and “4K” at 4096×2048. These are agreed upon formats but they cannot be broadcast in the US.

Frequency

The first television broadcast standard in the US was in 60 Hz and it remained that way until 1953, when color TV was introduced. The chrominance signal caused interference with the FM sound carrier, so to reduce that, they dropped the frequency to 59.94 Hz. This was a slight modification then, but it has made things a bit confusing ever since, mainly because we humans like to round numbers up. So even though your camera might say it is shooting 60i, it is usually shooting 59.94i. If it says 30p, it is 29.97P, and if it is 24p, it is 23.98P. We’ll get into frame rates in the next section but you can see how a slight change to the signal makes things a bit confusing. What’s important though is that in the US, we always broadcast in 59.94 Hz regardless of resolution or original frame rate.

European countries, and any areas that broadcast in PAL SD, broadcast HD in 50 Hz. In HD, the resolutions and color are the same universally – it is only the frequency that is changed. Many HD cameras can switch between these frequencies, which allows them to work in all parts of the world.

So 59.94 Hz and 50 Hz are the only broadcast standards, but there are a couple of other ones out there that were developed to capture true 24P. The Panasonic VariCam has a true 60 Hz mode as well as the 59.94 Hz mode. This was developed so that 24P could easily be extracted for printing to film. For the same reason, many cameras have 48 Hz modes which allows for 23.98 PsF or 24 PsF output. PsF stands for Progressive Segmented Frame, which splits progressive frames into odd and even lines at 48 Hz. Unlike 59.94 Hz modes these frequencies allow for easy extraction of 24P content.

Frame Rate

In the US, before the days of progressive, all content was captured as 59.94 interlaced fields per second. A field consists of a set of odd or even lines of video. These fields are played back on top of each other (interlaced) to create an image. Because each field is captured at a different moment in time, the video image can appear to ‘tear’ if fast moving objects enter the frame. Many people associate 59.94 interlaced video as having the traditional ‘video’ look. It is often referred to in cameras as 60i or sometimes even 29.97i, but they all mean the same thing. So if someone asks you to shoot in 29.97 interlaced, feel free to set your camera to 60i or 59.94i.

When deciding on the HD broadcast standards, the industry came up with two resolutions: 1080 and 720. The 1080 spec allowed for 59.94 interlaced fields in a second, while the 720 spec allowed for 59.94 progressive frames in a second. Progressive capture allows for full images to be captured, instead of fields. This has some major benefits over interlaced, especially when working with fast moving action. However both 1080 and 720 resolutions support progressive capture; it is only the broadcast final product which must remain either in interlaced for 1080 or progressive for 720. Popular frame rates are 30P (or 29.97p), 24P (23.98P), and 60P (59.94). Some cameras will capture progressively and then pull down the video into an interlaced 59.94 stream, while other cameras can capture and store these frame rates natively. As long as the video is captured progressively the final product, even if converted to interlaced with a video pull-down conversion, will hold on to its progressive look

In Europe, and other countries that utilize the 50Hz video frequency, 1080 is broadcast at 50 interlaced fields per second and 720 at 50 progressive frames per second. 25P is a popular recording format, which resembles the look of 24P and can easily be converted to 50i or 50p for broadcast.

Format = Resolution + Frequency + Frame Rate

When you add all the elements together, you get your format. The only trick is that we often shorten the full description to make things faster. So here are a few examples of popular formats and what they are commonly referred to as.

1080 60i (US Broadcast 1080i Video) = 1920 x 1080 Resolution + 59.94 Hz + 59.94 Interlaced Fields

720 60P (US Broadcast 720P Video) = 1280 x 720 Resolution + 59.94 Hz + 59.94 Progressive Frames

1080 24P = 1920 x 1080 Resolution + 59.94 Hz + 23.98 Progressive Frames

720 24P = 1280 x 720 Resolution + 59.94 Hz + 23.98 Progressive Frames

1080 25P = 1920 x 1080 Resolution + 50 Hz + 25 Progressive Frames

1080 24P (True 24 for Film Out) = 1920 x 1080 + 48 Hz + 24 Progressive Frames

Camera Settings

Many camera models display these settings differently, which can add to the confusion. Here is are three examples from Panasonic and Sony cameras.

Panasonic HPX2700 – P2 VariCam

hpx2700Panasonic lists the Resolution and Frequency in the same line on top. Then your frame rate can be set beyond that. This can be confusing because frequency is often mistaken as the frame rate.

Sony PDW-F800

f800The resolution is called “System Line” to indicate the number of vertical lines of resolution. The frame rate is called “System Frequency” to indicate the capture cycle of the camera, but the base frequency is actually determined by the “Country” setting with NTSC Area being 59.94 Hz, and PAL Area being 50 Hz. If recording 23.98 on this camera, the output of the camera will change to 23.98 PsF.

Sony SRW-9000

srw9000The 9000 will only capture images in 1920 x 1080, so no resolution options are listed. Furthermore, there is no frequency choice; instead you choose only the frame rate and the frequency will change accordingly. Here the frame rate is set to 59.94 progressive frames.

It is important to note that not all cameras can shoot every format. For example, the SRW-9000 above is one of the few cameras that can record in 1080P at 59.94 frames per second. Usually the manufacturers will list exactly what formats their cameras can record in and output. There are a large variety of cameras out there each supporting different resolutions, frequencies, and frame rates. So make sure to research a cameras’ specific functions thoroughly before investing.

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