Digital BW, The Print

But Austin, If you had a 16x24 print from a velvia slide and the same
size from a 20 megapixel camera, (with a top of the line Leitz, Zeiss,
Canon, or Nikkor Lens), could anyone on the planet see any difference,
anywhere in the print? I doubt it very much. Of course if you're
speaking of billboard size prints, you'd need the 100 meg. An 8x10 print
from a Canon D30 absolutely equals a velvia slide. Ther is no question
about it. I've done this comparison many times. You just can't see any
difference that's worth talking about. Your figures may be correct, but
what difference could it possibly make? 

Jerry


Austin Franklin wrote:
> 
> > Rather than comparing grain size to resolution, I think an interesting
> > comparison would be between the film's resolving power and the digital
> > resolution.  The data sheet for Fuji Velvia, for instance, says it can
> > resolve 80 lines/mm at a chart contrast of 1.6:1.  The
> > measurement for this
> > is described in ISO 6328:2000.  Does anyone have a copy of this?  What I
> > don't know is if lines/mm means lp/mm.
> 
> Hi Thomas,
> 
> lp/mm means line PAIRS per mm.  One black line, next to one white line.  If
> you have two lines of same color next to each other, then you can't see
> them.  Reason for solid black next to solid white is because it's %100
> contrast.
> 
> Resolution of digital imaging systems is hard to measure...since they have a
> regular structure for their arrays.  The worst case is diagonally...which is
> typically about 1.4x worse than on axis...and most digital imaging systems
> list only the BEST they can do, not the worst!
> 
> > If you assume it means exactly what it says, "lines/mm," then that
> > translates to 4064 pixels per inch which would mean an image of
> > 3840 x 5760
> > (or 22.1 megapixels) is equivalent.  This is closer to the number
> > thrown out
> > by Gordon Brown.
> 
> 80 line pair/mm is actually 160 lines/mmm, which is what you used to do your
> arithmetic with apparently...since 160 x 24mm = 3840.
> 
> The big issue to remember when comparing digital imaging sensors to film is
> that digital imaging sensors are regular patterns, and film is not.  This is
> very important when trying to compare resolutions.  Film has a LOT more
> information than just comparing squared segments (as you are doing when
> calculating digital equivalent based on lp/mm)...remember the diagonal issue
> I mentioned above.
> 
> You are also confused by pixels vs sensors.  Digital imaging sensors use
> FOUR sensor cells to make ONE color pixel...so if you want to get the same
> amount of color information, you need four times the amount of sensors!  So,
> 4 x 22.1 is reasonably close to my claim of 100M pixels.
> 
> There is also another issue...called sampling.  In the digital world, you
> need to sample at slightly more than 2x the smallest thing you want to
> RELIABLY detect.  So, in order to RELIABLY detect 160lines/mm (only on axis,
> off axis is 1.4x), you need to sample at 320 lines/mm...in both axes (X and
> Y), therefore giving you 4x your initial estimation of 22.1 M pixels, and
> this doesn't take into account the Bayer pattern (four sensor cells for one
> color pixels worth of information).  Again, showing that more like 100M is
> in reality what is needed to equivalent top 35mm film.
> 
> So, even the 80lp/mm shown for Velvia, clearly shows that 22.1M sensors is
> clearly not enough to give a reliable 80 lp/mm with digital.  Others will
> argue that anything over 40 lp/mm is wasted...and that very much depends on
> what your shooting techniques are.
> 
> If you want any of this explained any further, I'd be more than happy to.
> 
> Regards,
> 
> Austin
> 
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