I also tried to print a PSD file with layers and Qimage only picked up the bottom layer and ignored the rest. Does this mean I should flatten the image before printing ?
The DNG file has a "sidecar" file that is an Adobe exclusive.
In order to carry the adjustments you made, you would have to create a TIF or a JPG from the adjusted file.
As to the PSD, Qimage reads PSD files and prints them whether they are flattened or not.
Look at your PSD and see what is going on.
You are aware that PSD files must be saved with the Max Compatibility box checked.
Fred