Hi Matt,
Its strange that the single most important thing when working in PS is the one thing you didn't mention....the PIXEL dimensions! LOL.
That aside here's an attempt to clarify what's going on.
Put simply any image you have in PS can be PRINTED at ANY size.
There are 3 values that need to be considered:
1. The dimensions of the image......in PIXELS.
2. The resolution.........................in PPI (mistakenly named DPI in PS)
3. The printed output size.............in meters, mm, parsecs, whatever.
The calculation itself is no more difficult than A = B*C but, there are many different ways of using that formula to get what you want, and that is usually where the confusion comes in.
In your case you know the OUTPUT size and from what I can gather you know that you want to print @ 300 PPI.
Therefore the formula equates to:
Output Size (in inches) * PPI = dimensions in PIXELS.
What this means is that to PRINT a document to a certain size, at a certain PPI you have got to have 'x' amount of pixels.
Now, it may be that the amount of pixels in your image are fixed, in which case this limits you as to what PPI you can use...
For EG:
Your image is 3000px wide.
You HAVE to print @ 300 PPI.
Therefore the biggest PRINT size you can have is 10" wide. (3000 / 300 = 10)
Now, it may be that this is not big enough, (well we know it isn't...), so that means with a fixed pixel dimension AND a fixed print size the PPI has to change...
For EG:
Your image is 3000px wide.
You need a PRINT 100" wide.
Therefore the maximum PPI you can set is 30. (3000 / 100 = 30)
Now, that PPI may be too small for a decent quality print and will have that 'pixelated' look.
So, what to do?
Well, there is only one thing you can do and that is to 'upscale' the image, make it bigger in terms of how many pixels it has.
This is generally frowned upon and avoided at all costs but sometimes its your only option. Upscaling also degrades the image as 'pixels' have to be 'made up' from sampling the surrounding pixels. the amount of degradation is of course dependant on the pixels in the image, how many there are to start with and by how much you 'upscale' it.
If OTOH you have enough pixels in the image then no problem...you can either set the PPI to give you the correct OUTPUT size OR set the output size which will tell you the maximum PPI.
So, as you didn't specify the pixel dimensions I can't give you a more exact calculation but you can see from the above that basically you cannot have your cake and eat it.....if there aren't enough pixels in the image to give you the right print size at a certain PPI then you have to upscale.
If there are enough pixels then the output size may not give you the PPI you want for a decent print.
Likewise, a fixed PPI may not give you the output size you need.
I appreciate all that may seem a little daunting at first but it really isn't that complex.....if the numbers don't work out then something has got to give...be that the pixels, the PPI or the output size....its all a matter of 'balance'.
If none of that makes any sense then don't worry, we'll get there.
Sorry if I've mentioned stuff you already know, its just easier to say it all regardless.
Regards.
MrTom.
