How Many Megapixels Do I need?
This may seem like a strange answer but, it is not the number of pixels but the size of them and the size of your sensor that is also important. The question is important though, as companies use the number of pixels their cameras have as key feature and selling point.
Why do they do this?
Well it is easier for a lay person to understand, “this camera has more pixels than that camera and I know pixels are important, so this one must be better”.
All the camera manufacturer had to do was double the number of pixels on a sensor was to add 40% more pixels to the height or the width. This additional 40% though would only make a small difference in image quality but have a large effect on the number of mega pixels.
This sounds like there was a cold war pixel race between companies?
In 1991 to get a good quality 4×6” print you needed a 0.3MP image and that was great, in the late 90’s when digital started to gain speed most cameras had 1.2 or 2MP sensors, which with some printing resolution manipulation could still meet the majority of printing needs. It did this by using the best resolution for the viewing distance, the bigger you print the further back people stand from the print. When you print a billboard you are going to view this from about 300 meters to see the whole board. For a billboard a 6MP image is fine.
For the last 15 years we have had a Megapixel race with digital cameras and a second race is also taking place in the camera phone market. In 2005 the average number of Megapixels in a DSLR was around 6, in 2008 it was 10 and now in 2013 it is 18.
With so much choice in the number of pixels a camera has, which is best?
It really depends on what you are going to be doing with the image. For the average person who takes pictures and shares them on social media and may print them from time to time but no bigger than a 6×4” print uncropped, you will need no more than 4MP. Yet most people now do crop their images, be it with Instagram or even on Facebook and Twitter, to be safe I would say 6MP would be fine.
Wait, Nikons Cheapest Coolpix camera has 16MP, is this a scam?
No it is not a scam but I would ask; what size is the sensor and the pixels? Head here to find out why size matters.
16MP that they are stating the camera has is for the best quality image, there will be other options inside the camera that will allow you to shoot at a different resolution therefore with a lower number of pixels
For someone who wants to shoot and print (10×8”) as well as share on Flickr as well as social media with some room for cropping, you would need about 16 megapixels.
How did you work that out Mr Smarty Pants?
With maths and some basic assumptions. To calculate the number of pixels needed in your camera I will make the assumption that the image will be; printed, put on the web or viewed digitally. The optimal resolution for a print image is 300PPI and for web 72PPI.
Using these assumptions we can calculate the number of pixels needed using a simple formula; (Width inches X Resolution) x (Height inches X resolution) =Number of Megapixels.
For a 10×8” print (10×300)x(8×300)= 7.2MP. This is not 16MP as I said earlier but digital sensors are not scaled to 10:8 ratio so cropping of a larger size must take place.
For social media (using Facebook as the standard), an images maximum size is 2048px x 2048px. This time we just multiply the two sides together to find out the number of megapixels that is needed. For social media it is 4.1MP.
Wait, Wait, Wait, 300PPI? What is this?
300PPI (pixels per inch) is the optimal resolution for printing. This resolution would represent 300 pixels in one square inch, with each pixel having a colour tone and all nicely sat next to each other with no gaps.
When a digital image is prepared for printing the pixels are converted into dots and the dots have gaps between them. 300PPI translates into 150 DPI (dots per inch), which is the accepted standard for printed photographic image.
Printers (people and companies not necessarily machines) like to use rows or lines and use the resolution LPI (lines per inch). 150 LPI is 150 rows of 150 dots per inch, LPI and DPI can be converted 1:1.
150 LPI and 133LPI is the standard resolution for printing in magazines and books. Newspapers use a lower resolution of 85LPI for photographs and detail is lost in the image because the dots are plainly visible.
Ok, but earlier you said that a 6MP image could produce a billboard size print and now you are saying that 16MP can only produce a 10×8” print. HOW!?!?
Yes I was being a bit inconsistent and at the same time I wasn’t.
Viewing distance changes everything.
150DPI (dots per inch) or 300PPI is accepted as photo quality because an average person cannot see the dots at a few inches away. A darkroom print has no dots and this is the standard that a photo quality print is measured against. The further the viewer moves back from an image the more acceptable a lower resolution (DPI) is. A huge billboard may be printed at 40DPI about 80PPI but no one will see the dots as they are standing at least 50 meters away.
It is acceptable to scale down the resolution to make the print size bigger, a method known as up sampling. This is how Instagram images can be printed onto huge canvases.
How many Mega Pixels DO I NEED?
Once again this is a guide and I would not just choose a camera by the number of mega pixels but by the size of the sensor and the size of the pixels. Bigger sensors with bigger pixels produce better quality images. I would also recommend that you get more pixels than you need so that you have the ability to crop an image if you want to.
For an average consumer who may print occasionally but mainly shares on the web, I would say between 6 and 8 megapixels would be enough.
For someone more interested in photography and wanting to start out, 10-12MP will be about right. For an enthusiast I would say between 16-18MP.
As your interest grows in photography the more editing and cropping will take place with the aim of better quality images for output and more pixels will be needed.
Remember pixels don’t make the photographer; they are the slave to the photographer and his imagination.
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