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Friday, October 20, 2017 27° Partly cloudy

Auto Focus: Pixel Dimension

Published

By Albert Pedrosa

I often hear people that a medium format is best for billboards because it has higher megapixels. Is it true? Before answering that question, I’ll try to explain what resolution is in relation to camera sensors. Regardless of the sensor size, resolution is the number of photodiodes found in a sensor.

If you have a 24-megapixel camera, then it means that there are actually 24 million photodiodes or active pixel in your sensor plane and all of which will convert light into electric current which will then be converted into a digital color. Pixel dimension refers to the number of pixel lined up horizontally and vertically.

pixel dimension

A 5D Mark III would give you  5760 x 3840 pixels. If you will multiply the horizontal and vertical pixel count, you’ll get 22 million pixels. As advertised, 5D Mark III is a 22-megapixel DSLR camera. If you want to know the size in inches, you need to assign a number of pixels in an inch. For high-end printers, they will ask for 300 ppi. If you divide the pixel dimension by 300 then you’ll get 19.2 inches x 12.8 inches.

How can you print billboards from a 19.2 x 12.8-inch image?  Yes, you can. By using Photoshop, you can enlarge your image to bigger size. Photoshop will add pixels for you based on the color of the neighboring pixels. There are a few algorithm on how Photoshop assigns the color of a pixel but let’s just trust Photoshop on that for now.

Billboards are not supposed to be scary for photographers. It’s normally printed at a very low resolution. It can go as low as 20 dpi. Since billboards are posted far from the viewer, the pixels or dots in printing will visually merge due to the distance. What photographers should be afraid of are the large prints viewed from a close distance like wall prints or big posters. These are normally printed in high resolution.

A 20-megapixel camera is practically enough to create images for diverse commercial use. The size of the sensor will matter though. Note that a 20-megapixel cropped sensor or APS-C will have a smaller photodiode compared to a full frame sensor. A bigger sensor will always deliver a cleaner image in relation to color and luminance noise.

One of the advantages of a high resolution camera like the 5Ds Mark III or the Nikon D800 that carries a 50-megapixel full frame sensor is the option to crop your image and still get a good resolution out of it.

You probably want to buy a medium format camera not for the purpose of producing image for big prints but for a better dynamic range with higher resolution while still having a good clean image with less noise. The quality of the pixel will always matter when enlarging images.

Obvious examples are images produced by cellphone camera with 16-megapixel sensor. Even with a high resolution sensor, it will be disastrous to enlarge the image coming from a small-sized sensor. Bigger sensor is always an advantage but it comes with a hefty price tag.

Apart from the creative part of photography, technical aspect such as resolution will affect your image quality. Photography is always a marriage of technical and art. Keep on shooting everyone!

Albert Pedrosa is a commercial photographer who loves to shoot fashion. He teaches fashion photography and High-End Retouching at PCCI and maintains a studio in Malate, Manila for both commercial and creative works (Website: www.albertpedrosa.com / Instagram: @albertpedrosaph)

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