> Please suggest, how to read original image after resizing frame. You can't. The API is designed to pass the effect an input buffer; there's no way for an effect plug-in to "go upstream", and get the un-resized source media.
> Please suggest, how to display upscaled image on host after applying effect.
I'm not sure what you mean by "display", in the sentence above...? If the effect needs to resize the output buffer (which is what it sounds like you'd like to do), I recommend starting with the Resizer sample plug-in, from the AE SDK.