Brian writes, "I bought an LCD HDTV and the picture looks great on my local Comcast HD channels. I notice a lot of 'pixilation' What is that? Is that my TV, the feed, or the general current technology? I also bought a cheaper progressive scan DVD player. Why is the DVD quality so much worse then my cable feed? It looks OK, but not like the HD channels?"
There are a number of elements that might play into the issues you are facing, but without knowing specifics about the particular model of your TV, the way you are connecting all the devices, and the overall environment of your home theater setup, I'll need to make a few generalizations and then offer several potential solutions for you to try. There are a number of issues at work here, but they all boil down to differences in the quality of the video information for each content type.
Since you indicate the picture looks great on your Comcast HD channels, I'm going to assume the pixilated image you are experiencing with some channels is in reference to non-HD or standard definition channels. As you point out, your HD channels look significantly better than the alternatives. The biggest reason for a difference in picture quality is the difference in resolution between HD content and standard definition content. Most of the HD channels available through the cable and satellite providers broadcast 1080i content, which means the picture is made up of 1080 interlaced lines of image information. Standard definition television is 480i or 480 interlaced lines of vertical picture resolution.
Because standard definition contains less image information it will never look as good as HD content, but several factors can make it look better or worse. A few of the stations may be over-compressing their signal, which is fairly obvious when you see how much worse certain stations look on a plain old TV compared to other stations with crisp image quality. Stations sending a poor signal are going to deliver a poor picture just like any other garbage-in garbage-out method of operation. If all non-HD stations look bad on your screen, this is likely not the problem. One of the big factors in making standard definition look better on an HD screen is the amount of filtering built in to your particular TV. Some manufacturers go the extra mile and add special filters designed to improve the quality of the standard definition signal, specifically because most television stations are still broadcasting in standard definition.
The picture may also look better or worse depending on how well your screen scales the image from the standard 4:3 aspect ratio the more common 16:9 aspect ratio for HD content. Standard definition content is optimized for 4:3 which means the television is stretching the image to fit the HD screen. In general, stretching results in a distorted image, not a pixilated one, but you may be able to improve the image quality by turning off the image stretching feature on your TV and watching non-HD channels in their native aspect ratio.
When you connect your cable box to the television for HDTV reception, you need to use the component connectors in order to take advantage of the signal quality. There are mixed opinions about whether using the component connections to pass the standard definition signal actually makes it look worse. For some televisions people have found that using a component signal or S-Video cable improves the image quality for standard definition channels, although this is not true across the board. Another potential problem is line noise created by a cable signal that has been split several times before reaching your cable box. This is best avoided by running a clean line straight from the outside source to the back of the cable box. Attenuation do to lack of power for pushing the signal is also a potential side effect of splitting the signal. Asking the cable company to adjust the power of your signal often results in a massive improvement to the overall image quality of all channels.
The second problem you are experiencing with DVD images not looking as good as HD is again partially related to a difference in resolution. DVD video is 480p or 480 progressive lines of resolution where broadcast HD is typically 1080i. As more DVDs are released in HD, this problem will gradually go away. While you mention the DVD player is a progressive scan DVD player, you don't mention how the it connects to the HDTV. In order for you to take advantage of the progressive scan feature of the DVD player you need to connect the DVD player to the television using the component outputs rather than the S-Video or composite output. An additional possibility for improving your DVD image on the HDTV screen is to make sure the stretch feature of the screen isn't impacting the image quality of the DVD. For instance, if you are watching a full screen 4:3 DVD in the native 16:9 aspect ratio of the HDTV, you may experience some image distortion you wouldn't see when watching the DVD with the television's stretch feature turned off.