The perception of "sharp" will also be affected by the contrast of the colors and the softness/sharpness of shadows, plus any focal (depth of field) issues, in addition to the actual "rendering" settings discussed previously.

There are some color grading options in Iray, but you could also experiment with that some in post production.

For the shadows, a small light object, will produce a sharp-edged shadow in Iray, while a larger light-emitting object will produce software shadows, just like in real life.  Consider the difference between a bright flashlight and a large window.  (That's in addition to, or separate from, IBL contributions.)

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iClone 7... Character Creator... Substance Designer/Painter... Blender... Audacity...
Desktop (homebuilt) - Windows 10, Ryzen 9 3900x CPU, GTX 1080 GPU (8GB), 32GB RAM, Asus X570 Pro motherboard, 2TB SSD, terabytes of disk space, dual  monitors.
Laptop - Windows 10, MSI GS63VR STEALTH-252, 16GB RAM, GTX 1060 (6GB), 256GB SSD and 1TB HDD

As to the Iray render size, it has its own settings. Make sure that you have selected iClone Export Size in the Preview Settings:

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Thanks for the Tip 4u2ges, with so many options it good to be pointed in the right direction.
Cheers
N.

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View my latest Iclone project THEY ARE HERE Renegades versus the overlords 

Well, *the best possible* would comment with individual preferences.
But if you are looking to get the sharpest possible output and don't mind jagged edges iClone render produce,
then you may set Anti-aliasing Radius to 0 in Iray Render settings and avoid using denoiser.

I did a few test shots in iclone with iray using 500 iterations and 1200 iterations but I find the images are a bit soft and not as sharp as an iclone render grab, should the iterations be higher?
Also when you save out the still image of the iray and the still image using the iclone export, the iray image is about 10 / 15% smaller?
I do like the iray stills in iclone but how to get the best image possible I'm not too sure at the moment,,,,,all very new.



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View my latest Iclone project THEY ARE HERE Renegades versus the overlords