If I tell you something you already know please disregard it.
By the time I posted my reply you had added that your STB has DVI. We still need to know if you are watching HD programs or SD programs to understand your examples.
Originally Posted by split63
I recentely received my 7178 and I have it connected to a Comcast STB from Motorola via Component cables. The STB does not have HDMI.
What model STB do you have? Unless it's a very old one it should at least have a DVI output port. If it does then you can connect to your TV's HDMI port with a HDMI cable that has a DVI connector on one end. Of course if you don't have a HD STB then component outputs are all you will have. You diidn't mention HDTV so we don't know what you are watching on your new HD TV set.
Your Comcast STB does have configuration screens. You need to contact Comcast to get instructions for entering the configuration screens. If you provide the model of your STB someone here can probably help you.
One thing you need to double check is that the STB is configured to work with a wide screen TV and that it's not configured to work with an older 4x3 CRT TV.
I also have a progressive scan DVD connected via component cables as well.
When I play a DVD, the image fits the screen left to right with proper aspect, but I do have about 2 inches of screen top and bottom with no image.
Movies come in several different widths. You can read about that by following the "Black Bars" link at the bottom of my post. Depending on the movie, black bars can be normal top and bottom. They can also be normal on each side of the image, and in some cases they are normal on all four sides of the image.
Your DVD player also needs to be configured to work with a wide screen TV. If you just replace an older 4x3 CRT TV or just bought a new DVD player, the chances are that it's not configured to work with a wide screen TV. You need to find a setup option where your choices are 16x9(wide screen) or 4x3 (standard screen) and be sure that 16x9 is selected.
The HD output from the Comcast STB is worse yet. In 16:9 more, the image is stretched wide.
Both the STB and the TV have to have the correct settings. I don't own a HLS TV but you should have a "Picture Size" option using your remote that give you an image the perfectly fills your screen provided you are actually watching a HDTV broadcast.
In 4:3 mode the image aspect ratio looks right, but the image is in the center of the screen with large black no image boarders on all sides.
That's exactly how the image should look.
If I use Zoom1, the image fits the screen left to right, but the image extends beyond the screen top and bottom.
Again that's exactly how Zoom1 should look.
The comcast box has no apparent adjustment.
It has options for selecting the output resolution you want it to use, and an option to tell it what type TV screen you have.
What is the trick to make the image fit the screen?
If the image wasn't created to exactly match your screen size, then the only way to fill the screen is to enlarge, crop and/or distort the image.SD
TV comes with an image that is 1.33 units wide for each unit high.HD
TV comes with an image that is 1.78 units wide for each unit high.
TV comes with a screen that is 1.78 units wide for each unit high.
Some movies come with an image that is 1.78 units wide for each unit high, or 1.85 units wide for each unit high. These movies will fill your screen without any loss of picture quality.
Some movies come with an image that is 2.35 units wide for each unit high. These movies will need black bars top and bottom, or you will have to crop some of the image.
Some movies come with an image that is 1.33 units wide for each unit high, which is the same as SDTV. To fill the screen with these movies you will have to distort than by stretching them if you want to fill the screen.
What you own is a TV with a fixed size screen. The screen size is a compromise because one screen size can't fit all the different medial sizes that are available.
Your question is a very common one, so every once in a while I try to explain it from a slightly different angle.