Equipment & Techniques > Cameras, Lenses and Shooting gear
Up-Rez and down-rez for comparisons - why?
Deardorff:
Am wondering why comparisons of digital cameras have to be up or down rezzed to make a comparison?
With film if I wanted to make a comparison I made prints of the same size from the same of similar film. Comparing a 35mm negative to a 120 negative to 4x5 negative to an 8x10 contact print was easy to so. Printed each to 8x10 and set side by side and looked. Got closer or magnified if needed.
Same with 16x20 size prints from various sized negatives.
Could then do them developed in specific developers or even printed on specific papers if we wanted.
Why isn't it that easy with digital?
ErikKaffehr:
Hi,
If you print any image it will be resized either in your editor or in the printing process.
Let's say we talk about 16x20" prints from my two cameras printed on Epson SP 3880 at 360 PPI:
16" at 360 PPI is 5760 pixels
The Sony Alpha 99 has 4000 pixels vertically, so it will be uprezzed 44% for a 16x20" 36PPI print
The P45+ has 5433 pixels vertically, so it will be upprezzed 6%
Now, assume you have 1" borders on that 16x20" so it will get 14"x18". In that case 5040 pixels are needed vertically at 360 PPI.
So, in this case the Sony Alpha 99 image would be uprezzed 26% and the P45+ would be downrezzed 8%.
Clearly, the printer driver will do it for you, but resizing algorithms in Photoshop or Lightroom are better than the ones in the printer driver.
That said, I would say that my experience is that there is very little difference between 24MP and 39MP in A2 size (16 x 23") prints.
Best regards
Erik
--- Quote from: Deardorff on April 24, 2015, 04:28:02 pm ---Am wondering why comparisons of digital cameras have to be up or down rezzed to make a comparison?
With film if I wanted to make a comparison I made prints of the same size from the same of similar film. Comparing a 35mm negative to a 120 negative to 4x5 negative to an 8x10 contact print was easy to so. Printed each to 8x10 and set side by side and looked. Got closer or magnified if needed.
Same with 16x20 size prints from various sized negatives.
Could then do them developed in specific developers or even printed on specific papers if we wanted.
Why isn't it that easy with digital?
--- End quote ---
MarkL:
Contact prints from film formats will all be different sizes so to compare them you need an enlarger and a lens to enlarge the image like you suggest. Since printing from digital is not an optical process if different cameras produce files with different amounts of pixels they need to be resampled to all produce the same prints size (or even size on a screen at 100%).
dwswager:
--- Quote from: Deardorff on April 24, 2015, 04:28:02 pm ---Am wondering why comparisons of digital cameras have to be up or down rezzed to make a comparison?
With film if I wanted to make a comparison I made prints of the same size from the same of similar film. Comparing a 35mm negative to a 120 negative to 4x5 negative to an 8x10 contact print was easy to so. Printed each to 8x10 and set side by side and looked. Got closer or magnified if needed.
Same with 16x20 size prints from various sized negatives.
Could then do them developed in specific developers or even printed on specific papers if we wanted.
Why isn't it that easy with digital?
--- End quote ---
The big problem with that is how do you show a print to your online audience?
In a way, since lower resolution is more standard than higher, by downreszing to a common size, you can compare two cameras at equal output. If larger size is the target, then I think upsampling to a common size would be more indicative. But you are correct in general that larger film and larger and higher pixel count sensors both have an advantage and that get subverted in a downsampling scheme.
Telecaster:
You can indeed compare the results of different electronic cameras/sensor formats via print. My approach is simply to make the best 15x20" or 14x21" print I can from each camera/lens config, then place the prints side by side and see how they look. I don't try to equalize pixel counts prior to printing, but I do make sure I'm putting at least 300ppi on the paper. This means sometimes up-rezing a bit.
The most significant things I've learned from doing this are: 1) All my current gear can handle 15x20/14x21" with ease; and 2) All my current cameras, when fitted with top quality lenses, can resolve spatial detail that can't be seen in a 15x20/14x21" print from my Epson 3880. This happens to be my largest print size aside from the rare ~15x30" pano. :)
-Dave-
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