Ever wondered why so many “technophobes” within the photography world scream and rant about images not being perfect and why the big hubbub about resolution?
There has been a huge amount of techno babble about cameras needing more resolution for some time if you want highly detailed images, that are crisp, accurate, well focused etc. No doubt you heard the arguments. Most likely you’ve heard people say that pixel peeping is a fools errand. And you know what, by and large they are right.
And right about now I can see all the naysayers heads shaking and plans being made to burn me at the stake for speaking such heresy.
So just what do I mean by this statement? Consider my Canon 650D. It has an 18 million pixel sensor. Thats a lot of pixels collecting light. But how does my Canon 1000D compare with just its measly 10 million pixels? Pretty good actually.
Many camera owners have noted that attached to their images in the Exif data is a supposedly native DPI setting, which one is led to believe to be the resolution of the image needed for printing. Its a false reading, that is supplied for reference for printing. We will get to this shortly.
My Canon 650D with its 18 million pixels outputs a file that is 5184 x 3456 as its maximum file size. This is what the camera measures, not DPI or any other mythical information. Cameras work in pixels and thats it. Lets see how this translates to image size, and this is where things can get pear shaped.
The image above is the RAW image from the camera imported into RawTherapee. The Exif data is shown with the sensor resolution shown at right (highlighted). There is no inclusion of DPI data as it has nothing to do with the RAW file data.
If we use the calculator we find that we have an image that can be printed at 72 x 48 inches at 72 dpi. Thats a pretty big poster. It would intended to be viewed from several feet or meters from the image to get a true feel for the scale of the picture. How likely are you to notice any minor discrepancy in an image of that size when viewed from the correct distance? If I were standing directly in from of this image and was viewing it from two feet away would I see the dots in the image from the printing process? Probably but I shouldn’t be viewing at this distance.
Most printers, commercial print house and your own personal printer at home have a default resolution of 300 DPI (Dots Per Inch) as their base printing resolution. This ensures a good fine quality print with good colour rendition, brightness and accuracy. Some home printers do this very well, others no so much. My Epson L365 Ecotank produces excellent prints, with accurate colour tone and resolution and fine detail.
For higher quality, considered as archival at 600 DPI is also achievable on your home printer depending upon the use of archival photo paper to ensure longevity.
Now lets use the calculator again and this time we will select 300 dpi and see what we get. Remember we haven’t changed the original file size, we are only selecting a DPI rate at which we wish to print. We now see that the recommended print size is only 17.28 x 11.52 which is fractionally bigger than a standard A3 sized print ( A3 = 11.7 x 16.5 inches ). Thats quite a dramatic reduction in size from our original poster size, so what does this mean? Its really just a recommendation as to the largest print size at this resolution that retains all the detail in the image. Can you print larger at this DPI? Certainly but you can find that the quality of the image at a larger size does start to show some degradation. Theres a number of factors at play here that can influence the outcome, not the least of which is the cost, which is considerable when printing high dpi images above the recommended size. If you choose to do an archival print the image will be considerably smaller than the 300 dpi print.
The next image is taken off my smartphone from a visit to the local eye-wear shop. The sensor in the camera is 13 Mp and has a file size of 4128 x 3096 pixels. I wont delve into the differences in resolution between an 18 Mp aps-c sensor and a 13 Mp 1/2.3 tiny smartphone sensor. Suffice to say the detail & resolution is far superior with the aps-c sensor, which is why I never advocate cropping more that about 20% on a smartphone image no matter how good the manufactures like to tell you their cameras are.
What the calculator does tell us is that this image printed at A4 size at 300 dpi would be fine. In fact printed as a 10 x 12 it would be fine. With some editing the image could be cleaned up, rotated a touch and printed. But you wouldn’t want to crop it, click on the image and try looking at it at different zoom levels. Its pretty obvious that when you start viewing it a 100% or more it degrades very rapidly, in point of fact when viewed at 100% in RawTherapee and you look at the sign in front of the door you can see huge halos around the wording, and the more you look the more image degradation you can see.
If you apply the same process to the image of the Kingfisher image above you can see that even at 175% view the image holds together very well. Now consider that this image was cropped from an image the same size as the bird image above and you can see that I cropped it to approx 65% in my editor. Thats a huge amount of unused image and yet the image is still very nice and printed at 300 DPI looks even better. Smartphone images just cant match this.
That being the case why does anyone pixel peep? Pixel peeping does serve a purpose although it may not be for what is generally seen as the norm. Its a way of seeing if a sensor has deficiencies in its ability to capture, detail, colour and resolution, useful if you are checking a cameras technical operation but is essentially meaningless for the average photographer, who just wants good prints.
So what can we take from all this?
- Sensor size does matter when you want prints and not web sized images.
- Pixel peeping isn’t necessary for producing quality images and prints.
- Small sensors can produce very good print and screen imagery, just dont crop heavily.
- Check your camera output file size and print to recommended sizes as a rule of thumb, bigger is not always better.
- Use a file size & print calculator to help decide your maximum print sizes or speak with your local photography/print-shop for more info.
- Most images when viewed or printed at correct sizes dont show visual defects unless they are large.
Therefore dont get caught up on the pixel peeping rhetoric, for most occasions it has very little bearing on how your images look, its more important to consider composition, subject, light values and actually getting the image you want. Post Processing in my view is always best done to a minimum unless you have seriously messed up the image in some way.
It follows that you should not read too much into all the DPI mis-information either, DPI is only important to whoever is doing you prints. Once you have done all your editing work just ensure you save the image with the correct DPI setting so the printer can do its or their jobs correctly.
And remember photography is supposed to be a fun and rewarding enterprise no matter your level of skill. The old adage “Keep It Simple” is still very much of the essence.
Matt Granger expands on this subject a little in the video below and explains when working at 100% is beneficial for printing, and when you need to pixel peep for a reason.
Next article … DPI and what its used for.