ActionScript 3.0 :: Delete All The Images The Size Decreases To 81 MB Only?

This is my scenario

1: I upload an image

2: Without altering it,I make a copy of it and use it display to users in resized format note: I won't display the original image.

3:Now when user deletes the resized image,i need to delete the image loaded as bitmap i.e. the original image which i won't be displaying

For that I used bitmap.bitmapData.dispose() method.But,it doesn't free up the memory taken by the bitmap. For instance at initial state the memory usage is 58 Mb and upon loading 3 images the size increases to 87 Mb. And when I delete all the images the size decreases to 81 MB only. So,I feel the loaded bitmap is not completely removed.