What you should know about video processing.
The last few years have seen an increase in the number of video processing options available to the home theater consumer. I have seen an increase in the 'Amps, Receivers and Processors' forum wondering what video processing can do for them. This thread is an attempt to educate buyers.
Video processors in receivers can perform a number of tasks. From my experience, people tend to focus on deinterlacing and scaling. This article will focus mainly on those two features. But the video processing chips used in receivers may be able to perform other tasks such as noise reduction.
Before discussing deinterlacing and scaling, a little background may be helpful. For simplicity, this article will discuss TVs, but much of this article applies to projectors as well.
When discussing TV resolutions, there are two basic categories of display devices, CRT based and non CRT based. CRT based display devices are being rapidly replaced by addressable pixel displays based on LCD, Plasma or DLP technology.
Not too long ago, all displays were CRT (cathode ray tube) based. The US TV standard is often referred to as NTSC, named after the National Television Standards Committee. In the US system 525 scan lines, of which 486 are visible, are sent, but only half at a time (either the even scan lines, or the odd scan lines.) This is called interlaced scanning. This number of scan lines is often rounded off to 480 and an 'i' is added to indicate interlacing (p indicates progressive scan.)
CRT based TVs are being replaced by addressable or fixed pixel displays. These TVs have pixels which can be turned on and off individually. The picture made up of a bunch of pixels (picture elements) which can be independently controlled. These include LCD, plasma and DLP technologies. This includes projectors based on LCD or DLP technology as well.
Both CRTs and fixed pixel displays have a resolution. CRT resolutions can be specified in a number of ways, some of which are misleading. Fixed pixel displays resolutions are given by specifying either the number of vertical and horizontal pixels, or just the number of vertical lines. Common HDTV vertical line resolutions are 720p and 1080p. Common HDTV pixel resolutions are 1376x768 and 1920x1080. 1920x1080 is the exact resolution of a 1080p HDTV signal. 1376x768 is also referred to as 720p, but the exact resolution of 720p is 1280x720. I could not find a reliable explanation for why manufacturers use 1376x768, but the HDTV article in wikipedia has an explanation.
All fixed pixel displays have to convert the incoming signal to their native resolution. If the signal is interlaced, then they also have to deinterlace it. For example, a TV with a resolution of 1376x768 must first deinterlace a 480i signal and then scale it to match the TVs resolution. This is important to understand. Manufacturers put scalers into DVD players and then claim they will give you “near HD quality”. But if your TV is a fixed pixel display like most HDTVs, it HAS to scale to it’s native resolution. This makes this scaling ability in DVD players much less useful than in looks. The DVD player may have a better scaler chip in it than your TV does, but scaling isn’t particularly difficult. Also note that “near HD quality” is potentially misleading. Scaling an image to a higher resolution doesn’t add detail.
Deinterlacing is a harder problem than scaling. A receiver with a better deinterlacer than your TV may be helpful. For example, you may be able to use your receiver to deinterlace 480i from a cable box or game console and improve the video quality because your receiver does a better job of deinterlacing.
Without getting into too much detail, it’s perhaps useful to discuss why deinterlacing is challenging. There are two main problems to deinterlacing. The first problem is that interlaced scanning breaks the image up into two fields, that were usually captured at slightly different times. If all a deinterlacer did was to combine the lines, any object in motion would have artifacts caused by the fact that half of it is one place, and half in the other.
The other problem occurs when attempting to deinterlaced film material, such as off a DVD. Because films have a frame rate of 24 frames per second, and the NTSC standard is 30fps we have a mismatch. DVD players will use something called 3:2 pulldown to convert from 24fps to 30fps. 3:2 pulldown work perfectly fine for displaying a movie using interlaced scanning. Remember DVD players were designed back when most TVs used interlaced scanning. The problem occurs when some device tries to convert the image to progressive scan. If the device has no ability to detect that the signal it’s receiving is using 3:2 pulldown, it will combine fields from two different frames. A good deinterlacer can detect 3:2 pulldown, and assemble fields into frames correctly.
The details can be confusing. To summarize, deinterlacing is challenging, and some deinterlacers are better than others. There are some discs that can test the abilities of a deinterlacer such as the Silicon Optix HQV benchmark.
The best video processor can only correct some issues. When it comes to bad looking analog cable, there's not much hope. If the signal is ghosted, colors are distorted, the picture is fuzzy, etc, well then you have a bad signal. Bug the cable company to fix it, live with it, or upgrade to high definition cable when and if possible. Can a receiver’s video processor improve the signal? Certainly. But don’t expect miracles. Manufacturers always want you to believe that various features in their product will dramatically improve your experience. In my experience, dramatic improvements are rare. In my opinion, the last dramatic improvement for home audio/video was the DVD.
Hard code videophiles are more likely to see improvements in one video processor over another, because they have trained themselves for what to look for. For example, hard core videophiles are aware of a common DVD player problem called the chroma upsampling error. Most viewers won’t notice this issue. Casual viewers should not expect dramatic improvements from a receiver’s video processor, and may not know what to look for with subtle improvements.
Use the best deinterlacing solution available to you. This requires that you try out various settings in your video player and receiver. If you can’t see differences from one setting to the other, don’t worry too much about it.
Ideally, you should not be scaling multiple times. Consider TVs with a resolution of 1376x768. If you have your video player or receiver upscale a signal to 720p your TV will rescale the signal to it’s native resolution.
In summary, video processors in a receiver may or may not improve your video quality. Even though they may be able to convert a video signal to 1080p, that’s no guarantee your video quality will improve. They can’t add detail to the signal. If you want more detail, get a higher resolution source such high definition cable, HD DVD, Blu-ray or a high definition game console. Also note that some receivers may be able to “upscale” an analog signal when converting it to HDMI, but may not be able to upscale HDMI signals. Make sure you understand the receiver’s exact capabilities.
The last few years have seen an increase in the number of video processing options available to the home theater consumer. I have seen an increase in the 'Amps, Receivers and Processors' forum wondering what video processing can do for them. This thread is an attempt to educate buyers.
Video processors in receivers can perform a number of tasks. From my experience, people tend to focus on deinterlacing and scaling. This article will focus mainly on those two features. But the video processing chips used in receivers may be able to perform other tasks such as noise reduction.
Before discussing deinterlacing and scaling, a little background may be helpful. For simplicity, this article will discuss TVs, but much of this article applies to projectors as well.
When discussing TV resolutions, there are two basic categories of display devices, CRT based and non CRT based. CRT based display devices are being rapidly replaced by addressable pixel displays based on LCD, Plasma or DLP technology.
Not too long ago, all displays were CRT (cathode ray tube) based. The US TV standard is often referred to as NTSC, named after the National Television Standards Committee. In the US system 525 scan lines, of which 486 are visible, are sent, but only half at a time (either the even scan lines, or the odd scan lines.) This is called interlaced scanning. This number of scan lines is often rounded off to 480 and an 'i' is added to indicate interlacing (p indicates progressive scan.)
CRT based TVs are being replaced by addressable or fixed pixel displays. These TVs have pixels which can be turned on and off individually. The picture made up of a bunch of pixels (picture elements) which can be independently controlled. These include LCD, plasma and DLP technologies. This includes projectors based on LCD or DLP technology as well.
Both CRTs and fixed pixel displays have a resolution. CRT resolutions can be specified in a number of ways, some of which are misleading. Fixed pixel displays resolutions are given by specifying either the number of vertical and horizontal pixels, or just the number of vertical lines. Common HDTV vertical line resolutions are 720p and 1080p. Common HDTV pixel resolutions are 1376x768 and 1920x1080. 1920x1080 is the exact resolution of a 1080p HDTV signal. 1376x768 is also referred to as 720p, but the exact resolution of 720p is 1280x720. I could not find a reliable explanation for why manufacturers use 1376x768, but the HDTV article in wikipedia has an explanation.
All fixed pixel displays have to convert the incoming signal to their native resolution. If the signal is interlaced, then they also have to deinterlace it. For example, a TV with a resolution of 1376x768 must first deinterlace a 480i signal and then scale it to match the TVs resolution. This is important to understand. Manufacturers put scalers into DVD players and then claim they will give you “near HD quality”. But if your TV is a fixed pixel display like most HDTVs, it HAS to scale to it’s native resolution. This makes this scaling ability in DVD players much less useful than in looks. The DVD player may have a better scaler chip in it than your TV does, but scaling isn’t particularly difficult. Also note that “near HD quality” is potentially misleading. Scaling an image to a higher resolution doesn’t add detail.
Deinterlacing is a harder problem than scaling. A receiver with a better deinterlacer than your TV may be helpful. For example, you may be able to use your receiver to deinterlace 480i from a cable box or game console and improve the video quality because your receiver does a better job of deinterlacing.
Without getting into too much detail, it’s perhaps useful to discuss why deinterlacing is challenging. There are two main problems to deinterlacing. The first problem is that interlaced scanning breaks the image up into two fields, that were usually captured at slightly different times. If all a deinterlacer did was to combine the lines, any object in motion would have artifacts caused by the fact that half of it is one place, and half in the other.
The other problem occurs when attempting to deinterlaced film material, such as off a DVD. Because films have a frame rate of 24 frames per second, and the NTSC standard is 30fps we have a mismatch. DVD players will use something called 3:2 pulldown to convert from 24fps to 30fps. 3:2 pulldown work perfectly fine for displaying a movie using interlaced scanning. Remember DVD players were designed back when most TVs used interlaced scanning. The problem occurs when some device tries to convert the image to progressive scan. If the device has no ability to detect that the signal it’s receiving is using 3:2 pulldown, it will combine fields from two different frames. A good deinterlacer can detect 3:2 pulldown, and assemble fields into frames correctly.
The details can be confusing. To summarize, deinterlacing is challenging, and some deinterlacers are better than others. There are some discs that can test the abilities of a deinterlacer such as the Silicon Optix HQV benchmark.
The best video processor can only correct some issues. When it comes to bad looking analog cable, there's not much hope. If the signal is ghosted, colors are distorted, the picture is fuzzy, etc, well then you have a bad signal. Bug the cable company to fix it, live with it, or upgrade to high definition cable when and if possible. Can a receiver’s video processor improve the signal? Certainly. But don’t expect miracles. Manufacturers always want you to believe that various features in their product will dramatically improve your experience. In my experience, dramatic improvements are rare. In my opinion, the last dramatic improvement for home audio/video was the DVD.
Hard code videophiles are more likely to see improvements in one video processor over another, because they have trained themselves for what to look for. For example, hard core videophiles are aware of a common DVD player problem called the chroma upsampling error. Most viewers won’t notice this issue. Casual viewers should not expect dramatic improvements from a receiver’s video processor, and may not know what to look for with subtle improvements.
Use the best deinterlacing solution available to you. This requires that you try out various settings in your video player and receiver. If you can’t see differences from one setting to the other, don’t worry too much about it.
Ideally, you should not be scaling multiple times. Consider TVs with a resolution of 1376x768. If you have your video player or receiver upscale a signal to 720p your TV will rescale the signal to it’s native resolution.
In summary, video processors in a receiver may or may not improve your video quality. Even though they may be able to convert a video signal to 1080p, that’s no guarantee your video quality will improve. They can’t add detail to the signal. If you want more detail, get a higher resolution source such high definition cable, HD DVD, Blu-ray or a high definition game console. Also note that some receivers may be able to “upscale” an analog signal when converting it to HDMI, but may not be able to upscale HDMI signals. Make sure you understand the receiver’s exact capabilities.
