Cropping an image that retains some Megapixels

Hi...I was wondering if anyone can advise my. If i shoot in Raw and then heavily crop an image is there a way i can do it and the image will still be more than say 5/6 MP. At the moment if i have a bird picture that I like and I want to focus in on the small bird the file size obviously is reduced dramatically and as a result I can't then put that file onto certain sites that have a minimum size requirement ( 3/4 MP ) because that image is now 1/2 MP. Any advice would be warmly received.........I actually shoot in Jpeg at the moment and realise that this probably doesn't exist with JPEG files but Raw maybe..? My camera is a 18 MP camera! Thanks

Cropping and the number of pixels the final image has are two separate and different activities. Once you take the pic, you have captured the data in the form on an image. This is all the real data you have to work with.

When you crop you remove data. There is no way around that. You take your original data set, choose a portion of that data and toss the rest.

What you can do is re-sample after you crop. This allows you to set the pixel count to any number you wish. However, the pixels are not real original pixels. They are an interpolation based on the remaining pixels, a best guess of what the pixel would have been if there was a real pixel to capture the light.

If you shoot then crop the RAW image, you can always go back and amend that RAW image...provided that you saved the original RAW image. Is that what you were asking?

No. The things they do on CSI are make-believe and not possible in the real world. You capture a certain amount of detail when you take an image, anything not captured at that time is lost forever. You can get a computer to guess (but they give it a fancy name - extrapolate) what detail may have been there, but that's all it is - a guess.

If you are cropping 18 MP images down to less than 2 MP you are very seriously in need of a longer lens.