I have a digital picture with a size of x*y pixels. I'm trying to figure the maximum print size I could produce and still have an image which "look good" (relatively to human perception at a given distance).
So far, I have been using basic math and the notion of the human eye resolution to think about it.
For a screen, it's relatively straightforward :
- Say that 1 pixel of my picture = 1 pixel on the screen (=3 sub-pixels RGB)
- Compute physical distance between pixels on the screen
- Compute the perceived angle function of the distance between screen and viewer
- Conclusion : if the perceived angle is superior to the eye resolution, the eye can see two distinct pixels and the image doesn't look good. I agree that this criteria of "good looking" is purely mathematic and can be discussed at length. It's all I have got so far.
When it comes to printing, it gets more complicated, as an undefined number of dots are needed for one pixel. Moreover, complex algorithms are in play (halftone and arguably dithering, even if I tend to ignore the last for now).
Is there a way to compute the number of ink dots needed to represent a pixel given the specs of the printer (brand+model) ? Is it a manufacturer "secret" ? Someone spoke of a native dpi specific to each printer (300, 600). In this context, the term dpi is confusing as this native dpi is the number of pixels - translated into ink dots - that the printer can represent on an inch of paper. Anyway, how is this conversion done ?
For example, the specs of my printer are 9600*2400 dpi (one dot = one drop of an unique ink). How can I translate 2400 dpi into something meaningful for my problem ? If the native dpi is 300, does it mean 1 pixel = 8*8 dots (2400/300=8) ?