Hi Rene -
Sorry it took more time than I thought to get back to you.
Thank you for the information you sent. That's exactly what I needed to know to make some recommendations.
You stated that:
(a) people will be able to view the final print from "very close" distances;
(b) you already have selected the background image.
Item (a) tells me that to appear sharp at such very close distances, your hard-edged graphics (ie, the Japanese logo) must be reproduced at 200 ppi or greater, preferably, more like 300 ppi.
The only way to do this without having enormous file sizes is to prepare the logo in a vector program such as Adobe Illustrator, Corel Draw or even Adobe InDesign. The logo should be saved and exported in a file format that supports vector graphics such as *.ai, *.pdf, *.eps, *.svg, etc. PDF is the file format most widely accepted by RIP software.
When prepared this way, the file size for the logo will be small and its size will be exactly the same whether you eventually print it 1 inch across or 6 meters across.
The next question is how to handle the continuous tone (ie, photographic) part of your product -- the background image. Currently, it is 20669 x 10335 pixels. This will become approximately 88 pixels per inch if printed at 6 meters by 3 meters. This is not terribly high resolution, but:
(a) It sounds like you don't have much choice in the matter - you are stuck with this image. Obviously, it will have to be up-rez'ed by about a factor of 3 or 4 in both directions to eliminate pixelation, but whether you up-rez it (say, with a specialized program such as Genuine Fractals), or you let the very capable Roland RIP software (essentially, the printer driver) do the up-rezing, the image will always appear slightly soft when viewed from distances of a foot or less.
(b) The existing image will probably be adequate when printed at your final size as long as the logo and any other hard-edged graphics are sharp. I, and many other people regularly make large prints at 50 ppi, and no one has ever complained that they were soft. See the discussion about this in the nice article that I previously cited:
http://graphicdesign.stackexchange....on-should-a-large-format-artwork-for-print-be
Of course, if you do the up-rez'ing to, say, 300 ppi, you will be forced to deal with 10x larger file sizes, whereas if you let the Roland RIP engine do the up-rez'ing you will only have to deal with the existing size of the background image.
So, my recommendation is to do exactly what is recommended in the articles I cited: Don't use Photoshop, but instead, use a program such as Illustrator that will allow you to bundle both vector and bit-mapped graphics in one PDF file. That gives you the best of both worlds. The logo and other graphic elements will be razor sharp, while the background image will be as sharp as possible, and the file size will be reasonable.
Again, you are facing an extremely common problem, and the solution that I am suggesting is the industry-wide standard way to solve it. The articles that I cited describe this approach (bundling both vector and bit-mapped, continuous tone imagery together in a PDF using Illustrator) in much more detail than I have.
Hope this helps.
Tom M