I am looking for a graphics library for specific features and such. But I am confused as to which to use... I know that there is SDL and Allegro. But I dont know if they do what I want them to do fully...

I am trying to start writing a game engine and I wanted to be able to include the following options for this graphics library:

Main feature:
Code does not need to be changed at all for cross-platform functionality and all the functions still remain the same. Basically, I just want to copy and paste the code, Compile the SAME EXACT CODE under windows, and linux and mac etc... Without modifying anything.

Platform Portability:
MUST:
Dos
Windows
Linux
Mac

Wishlist:
Amiga
Palm
Pocket PC/Windows Mobile

For: C++

Graphics file formats needed (All true color and high color and 256 color support):
MUST:
BMP
GIF
JPG
PNG
PCX

Wishlist:
TGA
ICO
ICL
CUR
IMG
IFF
WMF
TIF
XBM

Library Features:
Just some of the most basic features that a graphics library has. But a MUST is that it can compile in free C++ compilers. I am hoping that maybe the library can also support outputting and converting images to other file formats as well. In other words, open the file in JPG, but then save it in BMP, etc...

MUST HAVE FEATURES:
Color adjustments
Lighting adjustments


Can anyone help me find something exactly like this? Or is it possible to extend Allegro or SDL to be able to do this? Does something with my wishlist items exist? Thanks in advance for your help...