Technical questions about printing and DPI

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liverpool_f_

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Hi everyone,

I have now made 1000's of images and I am really looking forward to printing. I am one of those people who want to understand things technically before I jump in and I am afraid I am stuck on a number of technical issues as far as printing is concerned. This will be very dry so fair warning!

I want to print at 300dpi. I have scanned 35mm film at the highest resolution for my scanner before its optics cannot give better results. This is 3600dpi for the 35mm, giving an image that is 300dpi at slightly smaller than a3 size. I would like to print my best images at a3.

This is my question;

If I upsize my images to a3 without upsampling, the DPI will drop below 300, probably to around 270 or 280. Can a printer actually physically print in a sliding scale of DPI and just print at 270 DPI giving a print of good quality that does not require upsampling (and the subsequent loss of quality that interpolation will cause?)

Or

(as I suspect) will the printer/printing software resample image to 300 dpi (and probably to a worse job of it than I would do myself in photoshop?)

I will happilly accept slightly below 300dpi if it means not having to upsample my images. However, if upsampling is going to happen in the background, I would rather do it myself and prepare images specially for printing.

I have been trying to find the answer to this question online and among my technically adept photography colleagues and I haven't been able to get to the bottom of it. I hope there are some techy printer folks out there who know the amswer to this!
 
Good question! But you need to say whether you're on about home printing or sending to a commercial printer.
 
My old 16mp camera gave slightly less than enough pixels to print A3 at 300dpi
The print looked fine at 270dpi and I am sure yours would too
So no it doesn't automatically upscale, you can choose what dpi to use from your printing software
 
Be prepared to receive lots of contradictory advice! FWIW here's what I do:

Being a control freak I don't hand over any processing to the printer driver/software - I don't have enough knowledge to predict what it's going to do, and I don't want it making decisions for me
I resize my image in Photoshop to the print size that I want at 300ppi, if possible.
If I can't achieve 300 ppi at the print size I want, I'm perfectly happy at 240ppi (I can't see the difference viewing from 12inches, or so)
I know one accomplished photographer, whose prints are exhibited nationally, who regularly prints at 180ppi
I would rather take this approach than upsample, but I understand that other opinions will differ.
Develop a reliable technique that suit your purposes and stick with it is my advice.

By the way, I normally mount my prints on backing board that's 500mm x 400mm and I print on A3 paper with the image size about 350-360mm on the long edge. IMO any larger and the image "overpowers" the mount.
 
Thank you all for your fast and more importantly, well considered answers. What I have taken from this is that 300 dpi is not a magic number and any print resolution in the vacinity of 300 will render almost identical results. The printer will print at whatever DPI you tell it to (up to it's maximum resulotion) and doesn't work in 'steps' of DPI e.g. (72, 150,300)

I also like the point about mounting on the backing boards. I had not considered that my A3 prints could actually be smaller than a3 to account for cutting the paper and also mmounting it in preparation for display.

If I have made a fundamentally wrong deduction from what you have all said, I would appreciate being corrected on what said above
 
Conversely, If I am printing my large images in a smaller size, for example an image that is 300 DPI at A3 size, but is being printed in A5, is it problematic to send an image with a very high DPI to the printer? Will the printing software have to process the image to reduce the DPI to something that the printer can handle, or will most modern, professional photo printers be able to deal with it and print it in a very high DPI
 
Generally speaking, only photographers will examine an image up close.

Assuming 20/20 vision...

At a standard reading distance (for example 12") the eye can only resolve about 300 ppi.

At a standard monitor distance (for example 30") the eye can resolve about 115ppi.

At a TV viewing distance (for example 6 feet) the eye can resolve no better than 50ppi.

Looking at a cinema screen distance (about 40 feet) the eye can't do any better than 7ppi.

Sadly the source for this is now behind a paywall, but the principle is sound. If you're printing to A3 and viewing from a reasonable distance (say 30") 115 ppi is absolutely fine. My 35mm scans are done at 2300 x 3500 (ish) which results in around 200 ppi at A3 and is perfectly acceptable. At A2, this drops down to about 145 ppi which is still perfectly acceptable because you tend to need to move a bit further back.
 
liverpool_f_ said:
Conversely, If I am printing my large images in a smaller size, for example an image that is 300 DPI at A3 size, but is being printed in A5, is it problematic to send an image with a very high DPI to the printer?
Click to expand...
I've never noticed a problem doing this.
 
liverpool_f_ said:
Conversely, If I am printing my large images in a smaller size, for example an image that is 300 DPI at A3 size, but is being printed in A5, is it problematic to send an image with a very high DPI to the printer? Will the printing software have to process the image to reduce the DPI to something that the printer can handle, or will most modern, professional photo printers be able to deal with it and print it in a very high DPI
Click to expand...
I have always prepared my files @300ppi to suit the size I intend to print. This has been based on that other than a few printed at home, I have used commercial printers.

FWIW one printer I used to use (since gone bust and phoenix like resurrected) and with a few images to print at the size I required i was under 300ppi, their printing software unscaled my files and the results were extremely good.

In other words prepare as needed to reduce impact of things outside my control.
 
I just printed loads of images from camera club members that don't really understand dpi and even A4 prints at 140 dpi look fine. I don't downsample my images to 300dpi as I figure I already have the colour of pixel that was there why would I let the printer guess what it is
 
wookie6262 said:
I just printed loads of images from camera club members that don't really understand dpi and even A4 prints at 140 dpi look fine. I don't downsample my images to 300dpi as I figure I already have the colour of pixel that was there why would I let the printer guess what it is
Click to expand...
I always print at 4800dpi horizontal and 1200dpi vertical :D
 
Dpi is a physical property of a printer and can't be changed.

PPI depends on pixel width and physical width. 3000px wide printed 10" is 300ppi and if you printed it 20" wide it would be 150ppi.

Upscaling loses quality anyway, and you're almost always better off just getting the printer to handle the resizing.

You can get away with larger prints with C type prints than you can giclee as well since the image isn't made up with dots of ink on a c type print.
 
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