Mike Chaney's Tech Corner

I've mentioned that recently I am printing contest-winning photographs (at 21x23") for excellent amateur photographers.  I then mount the photographs in a public outdoor exhibit gallery.   About 20-25 images/month.  ( I print all the images at the same size, so that I can efficiently frame and hang them with reusable parts.)

I use Qimage exclusively for printing (which means I don't know squat about printing from Photoshop or Lightroom, etc.).   I especially appreciate its assessment of what I'll call "real-pixel density" of the image file, relative to the size I am printing at.   Image files I get will vary from 40ppi to 300ppi.

About 15-20% of the images are Poor or Fair quality according to Qimage.  I have been going back to these photographers and asking them if perhaps they submitted a downsampled file for web use, etc.    They will do their best to send me a new image file -- sometimes the files will go from 100K to 30megs!   I guess they just ticked the box that said "superresolution" or such.    Somehow, Qimage knows that those aren't real pixels.   The ppi doesn't change.

Here are my questions:
1.  Some images seem to work ok at "poor" ppi -- the nature of the image may not be something that demands precise detail.   Are there some guidelines that might help me know when to work harder with a photographer to get a better image, and when to "let it go"? 
2.  Are there any tutorials on "preparing photoshop [or lightroom] image files for printing in Qimage" that I could offer the photographers?   A good number of them are not technically sophisticated, and just click on buttons with promising-sounding names.   
3.  How does Qimage assess ppi when the files have been "up-rezed" in PS or LR?  It seems to know that the pixels are made up!   How does it do that?  Just curious.
4.  Any other suggestions for me in helping these photographers?

My next idea is to do a workshop environment where the photographers who get it right look over the shoulders of the photographers who get it wrong -- and adjust their practice.   One workshop for LR users, one workshop for PS users, etc.    I don't know this stuff well enough myself to help them.

Advice appreciated.

Qimage doesn't care about anything but pixels in the image and how large you print.  If someone says they "enlarged" the image, they must have not added any pixels and maybe they just changed the embedded size because Qimage isn't trying to detect fake vs real pixels.

As to what you should tell people, that's super simple.  Just tell them to do anything they want with respect to editing but DO NOT under any circumstances resize the image or add/remove pixels!  Qimage will do a better job upsampling than Lightroom or Photoshop so just make sure the people submitting photos do not alter the pixel resolution of the images.  Qimage will take care of that at print time and it is important that Qimage know the original size (without any resizing or resampling).  If you add "fake" pixels with second rate interpolation like those in Lightroom or Photoshop, Qimage will assume those are real pixels and it defeats Qimage's interpolation algorithms.

Regards,
Mike