Agorabasta from what I understand (I could be wrong of course, I thought I was wrong once but I was mistaken) 1200dpi printer output is largely meaningless in relation to the MP of an image, the printer uses dot overlay to create a particular CMYK dot colour/shade, so you can end up with a double/triple blended bleed dot that approximates the colour of the original in RGB speak, in the conversion process (printer algorithm also has to convert screen 72 or 96 PPI into printer DPI) the so called 1200dpi output may still be no more than 300dpi in real terms, if it’s lucky.
The human eye can’t resolve dots any finer than about 60 dots per inch, but what the eye can perceive is density differences, a photo printed at 300dpi looks a lot better density wise than the same one printed at 100dpi even though the eye can’t actually see the individual dots from standard viewing distance in either case.
Of course image resolution
(size) as well as file type and size
do matter when it comes to getting an excellent print or a not so good one at a given print size
, also print settings, paper, ink and monitor calibration can influence the result.
That’s why as I’ve said before there is no visible difference in images printed on my photo printer between my 6MP camera my 10MP or 12MP cameras printed out at A4 size, at larger sizes like A3 the 10MP&12MP cameras will win for sure but I, like many people, don’t have an A3 photo printer, I wouldn’t know what to do with an A3 print anyway except maybe try framing one for the living room perhaps.