Picture format on the simple definition digital receiver output is 720 horizontal pixels and 576 vertical pixels.
For economic resons, provider can broadcast a TV with pictures with less resolution (less pixels).
The MPEG device in the receiver will be in charge to put the picture in a correct size for the display. Of course decreasing pixels changes the details in the picture.
To show this, some example of test cart broadcasted with different resolutions.
Test cart with max SD resolution 720x576:
We are looking on a detailed part of the test cart (yellow part), and compare picture with other test cart with less resolution.
resolution of 528x576:
resolution of 480x576:
resolution of 352x576:
We can see the effects due to less resolution, only the full resolution (720x576) do not alter the picture.