I need help evaluating different strategies for upping the resolution of an original file of 3504X2336 pixels
we need it to be printed very large ( 1meter by 3meters= 40x120 inches)
If you look at posters of a similar size on the street, you will find on getting close, that they are usually a very low resolution, 72dpi or even lower. Yet dspite that they look fine. Why? You tend to stand at a distance that is comfortable for viewing shot, which means it doesn't need to be as high a res as when looking at smaller images such as in magazines, which normally tend to fill one's field of view more than any other form of displaying images.
There were some shot in one of the local museums recently, which documented the rebuilding process and they were enormous. They looked great, despite the obvious low quality once you got a bit too close.
I know there are special tools with algorithms such as fractal etc... for this; also there is the step by step solution of slowly resizing it many times in photoshop bicubic; and there are also sharpening processes that may help, and finally printing processes may also increase apparent sharpness.
Try inceasing the size when opening file in ACR [if it's a RAW file], it's the best way I've found of increasing file size and I've tried the slowly resizing method and Genuine Fractals and ACR was by far the best.