The Truth About Megapixels
Today’s topic is megapixels. Camera manufacturers and advertisers are constantly pushing new expensive cameras with more and more megapixels. It is time to push back and stop spending more money than you actually need to. So, the question is just how many megapixels do you really need.
My first digital camera was a Fuji FinePix 3800. It was a 3-megapixel point-and-shoot camera with a digital viewfinder to look through. Yet even with its limitations, I was able to get many nice photographs with this camera. Here is an example. I took some shots of a young woman in costume as part of an annual parade. The contrast was tweaked a bit in Photoshop because she was standing in the shade. However, nothing was done to enhance the gradation or resolution.
I made an 8x10 print and photographed it with a sharp 100mm macro lens as seen below:
From a normal viewing distance of 3 feet, the photograph looks good. Then I moved the camera in for a close-up:
Now you can see some blocks of pixilation, but still nothing horrible. What stands out is the lack of sharpness. This is not pixel related but the result of using a cheap lens.
The thing that makes this 8x10 acceptable is that no normal person is going to get up close and look at a print with a magnifying glass.
Now for the data on megapixels. Suppose you must have that new 50-megapixel camera just in case you take a photograph to go on a billboard. This may surprise you but billboards actually, only need 2.1 megapixels and 6 megapixels are more than enough. Why? The answer is viewing distance. The further away, the fewer dots per inch (DPI) are needed. The lower the DPI, the lower amount of megapixels required.
Roadside billboards are viewed from between 500 to 2500 feet away. So from the below chart, 3 DPI is more than enough.
Viewing distance and minimum amount of DPI needed for a sharp image:
2ft / 0.6m = 300 DPI
3.3ft / 1m = 180 DPI
5ft / 1.5m = 120 DPI
6.5ft / 2m = 90 DPI
10ft / 3m = 60 DPI
16ft / 5m = 35 DPI
33ft / 10m = 18 DPI
50ft / 15m = 12 DPI
160ft / 50m = 4 DPI
200ft / 60m = 3 DPI
650ft / 200m = 1 DPI
Let us say you want to have a 24x36 inch print made at 300 DPI. The resolution needed for it is 5400x3600 pixels, which comes out to 19,440,000 pixels or 19 megapixels.
(I reviewed a lot of webpage articles and tables about megapixel/print size. Unfortunately, not all of them agree. Finally, I found a site that does the actual math based on what I entered https://www.scantips.com/mpixels.html. Another useful site is https://toolstud.io/photo.)
If your target is a computer monitor, tablet, or television screen, the resolution is around 2000 by 1000 pixels, which are about 2 megapixels. Also for full-screen webpage photos, the best size is 1920 pixels wide x 1080 pixels high. That comes out to 2 megapixels as well.
With this in mind, a 24-megapixel camera will produce a photograph with room for cropping. For most of us, money spent on a higher megapixel camera is a waste of money. Take the money you save by taking this advice and spend it on better lenses. The poor optical quality of a lens definitely shows in larger prints
- - David