Re: Why pixel peeping (usually) makes no sense

John Navas wrote:
There's a great difference between screen resolution (72-96 PPI) and
good printing, where rules of thumb for normal viewing distances are at
least 130 DPI for barely acceptable results, and up to 230 DPI for
excellent results. With current technology, anything more than 300 DPI
is pretty much wasted. This translates to:

4x6 5x7 8x10 11x14 16x20 20x30
------ ------ ------ ------ ------ ------
Acceptable: 0.4MP 0.6MP 1.4MP 2.6MP 5 MP 10 MP Very good: 0.8MP 1.1MP 2.6MP 5 MP 10 MP 19 MP
Excellent: 1.3MP 1.9MP 4 MP 8 MP 16 MP 32 MP
Best: 2.2MP 3.2MP 7 MP 14 MP 28 MP 54 MP

For my 7.2MP Panasonic FZ8, 11x14 is "excellent" at about 216 DPI.
The same effect on my high-quality 96 PPI display is 96 / 216 = 44%
zoom, more realistically 50% zoom. On a standard 72 PPI display it's
72 / 216 = 33%.

Even these reduced zooms exaggerate the issue, since display pixels are
so much bigger and more distinct than high-resolution print dots. For
this reason display zoom needs to be reduced even further for meaningful
print judging, to about 25-33% (depending on display) for a high-quality
(8MP) 11x14 print.

Because screen pixels are so much larger and coarser than good printing
dots (effectively a magnifier), zooming in more than this doesn't make
sense (unless the ultimate objective is screen display of 100% crop
rather than normal screen display or printing). If you can't see an
issue at this reduced display zoom, then you're not going to see it in
an excellent print either.

Thus my normal practice is to assess images on screen at no more than
33% zoom, zooming in farther only to examine the effectiveness of
sharpening and/or noise reduction.

This relationship does of course change for larger print sizes, but then
print degradation due to pixelation becomes an offsetting issue -- more
pixels are needed to make larger high-quality prints. When I anticipate
printing larger than 11x14 with my 7.2MP Panasonic FZ8, I shoot multiple
overlapping images and then stitch them together, multiple-frame
super-resolution. 4 image stitching is sufficient for excellent 16x20
and very good 20x30 prints, and even larger sizes can be produced by
stitching more images. In which case the same reduced zoom is
appropriate.


Shoot, hit the wrong button and send a blank replay, sorry about that.

Well I don't see how looking at the screen at %25-33% can tell you how the print is going to look, unless you are making a very small print. Say you start with 8MP and view at 25%, you effectively are throwing out 15 out of 16 pixels in your viewing, reducing your 8MP image down to 0.5 MP.

I say that many times differences that are visible at 100% view are hard to see in the print, you really need to print to tell how it is going to look.

I also would take some issue with your table of needed pixels, this is a personal thing. For an 8 x 10 print I would say 4MP is acceptable, but just and very good would be 8MP. And with a good printer you can see a noticeable improvement going from 8 to 16 MP for a 8 x 10 print, so I don't see how even 8MP could be call best for this size print.

A lot depends on the printer used, when I use Costco they can't seem to use detail much past 200 ppi, maybe a bit past but not close to 300ppi. With my cheap inkjet printer I can see detail to 400ppi.


The other thing that I have noted is over time I have found uses for higher resolution photos, part of this is making bigger prints and part of this is doing slide shows that have pan and zooms in them. I look forward to the day that I can have a 4 x 6 foot wall mounted display that has 200 ppi, that is going to take close to 140MP, and for it to really look clean you need to down size a bit, so you might want to start out at 200MP.

The point is you can never have too much resolution and your images can never look too clean. Maybe not for how you are using today, but what about 20 years from now?

Scott
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