cspear posted at 10:34PM Wed, 25 December 2019 - #4373084

Since I do this kind of printing for a living, let me throw in a few thoughts.

The 300ppi standard is based on really old requirements for photo-mechanical reproduction technology, where a 150 line screen was very common. A lot of the technology used for digital printing uses the 300ppi standard as the basis for its printing resolution, which can be 600dpi, 1200dpi, 2400dpi etc. Note the difference between pixels per inch (ppi) and dots per inch (dpi). Do not assume that you have to make an image (PIXELs per inch) match the print resolution (DOTs per inch).

A poster of this size is likely to be printed on an inkjet system, and it is highly unlikely that a regular dot pattern would be used for screening: it's almost certain to use 'stochastic' or 'frequency modulation' (FM) screening. Traditional screens rely on Amplitude Modulation (AM). AM means the dots get bigger to deliver more of a particular colour. FM means that there are more dots of a particular colour where required.

About 25 years ago I was involved in conducting research into how image resolution impacted on perceived printed results, and long story short, for most images the difference between the same image at 200ppi and 300ppi, printed at the same size using the same paper and ink (actually printed on the same page) was, if noticeable at all, negligible.

Images rendered out from 3D apps have not been softened by lenses, scanners, etc. so should not need artificial sharpening to 'improve' them.

A poster this size will be viewed mostly from a distance in excess of 1 metre and will not be scrutinised as closely as a print held in the hand.

Many of the more recent RIPs and print control systems have built-in upscaling engines which can, depending on the image, produce astonishing results even from poor quality originals. I did a job this week where a 900pixel x 600pixel image was printed at A3 (12in x 16.5in) and looked, well, not great, but by no means terrible.

With all that in mind, I'd be inclined to render out to 100ppi equivalent (2400 x 3600 pixels); keep the image in RGB, DO NOT convert to CMYK; and DO NOT apply any sharpening.

Wow. That is just invaluable information.

Just to add, Blender 2.81 has the Intel denoiser as a filter in its compositor. Which means you can use that filter on image files, like, say, Poser renders. Denoising has made my life considerably easier from the start, and I've seen comparisons show the Intel denoiser as better than both the nVidia denoiser and the Cycles one. Also, it doesn't need specific hardware or software, which the nVidia one does. That said, all of those denoisers are specifically good at raytraced noise. For instance, the Intel denoiser doesn't work on noisy digital photos or Eevee renders.