If you imported as a composition maintaining layer sizes then you should have no trouble unless the comp is rectangular pixels or your Photoshop file was set up with rectangular pixels, or AE is improperly interpreting the file as rectangular pixels because your Photoshop fils is a standard rectangular pixel frame size.
One more thing, for your artwork to be perfectly aligned you should be creating every element at a precise even number of pixels high and wide.
Show us a screenshot. Give us some details.
If you import a PSD as a composition with "Retain Layer Size", your anchor points will be the centre of each layer.
If you import a PSD as a composition without "Retain Layer Size", your anchor points will be the centre of the composition frame.
Charles Bordenave wrote a great little script that allows you to instantly correct anchor points, with plenty of alignment options as well as centre, and without moving the layer's position.
thank you for the replies.
it seems that i imported psd file as a composition but without "retain layer sizes".
However, when i import the psd as a comp with "retain layer sizes", all layers are positioned at the center of the composition, thus distorting the object (in this case a bicycle):
This wasn't happening when i imported the .psd as a comp without "retain layer sizes" - even though all layers' anchor points were at the center of a compositions, they were placed at appropriate positions, thus displaying a proper bicycle:
The "rectangular pixels" theory seems interesting but i could not find any setting or property of it in my photo editing program
Your mistake is that you did not open the composition created when you imported the PSD as a composition. Instead, you added all of the layers to a new composition. After Effects will do all the work for you, you just need to open the composition that was created.