PHOTOSHOP - Image resolution, high or low res?

As all digital cameras and Photoshop deal with Pixels, it is a good idea to understand just what they are.

A digital image is comprised of a matrix of light sensitive pixels (Picture Elements) called a bitmap, in much the same way as film uses a matrix of ‘grain’ to record an image, and newspapers, books and magazines use a matrix of dots in a screen to reproduce an image. The more (finer) grain you have, the sharper your image is. The same is true with pixels.

Photoshop is a pixel ‘editing’ program, so you can change the proportions of your image (rotate, distort or resize your image), you can re-colour it, or turn it to black & white, you can ad elements to it or remove them simply by changing the pixels. Your digital cameras resolution, or its ability to reproduce an image, is measured in Millions of pixels (Megapixels).
The images below show this.

2000 pixels wide

1000 pixels wide

100 pixels wide

50 pixels wide

10 pixels wide

1. Original frame but reduced to 72 pixels per inch

2. Original high res file size info

3. Original high res file enlarged to 300 percent

4. Original high res file enlarged to 1200 percent

5. Original high res file enlarged to 6400 percent

But let’s look at a very basic way of understanding your cameras resolution. Each frame of a 10 Megapixel camera at its highest resolution is 3872 x 2592 pixels or 10 million (Mega) pixels. This equates to a 28.7MB file, which is the equivalent of a high resolution 32 x 21 cm file for print, a little larger than A4. The image above of the trio at an airport in Tanzania was taken with a Nikon D800, you can see the file size in the info window, 149Mb!.

If we assume that modern computer monitors display roughly 2000 pixels wide, then each image on its long side is nearly 4 screens in width. This is by no means exact but it does give you an idea as to what this all means. A 17.5 Megapixel file is 5120 x 3427 pixels, and a 25 megapixel file is 6144 x 4113 pixels.

Now here’s where it gets a little more complicated. If we viewed (1) as an A4 image, we would probably be 30cms away from it. If we enlarged it to the size of (5), to get the same clarity as (1) we would need to view it from three to five metres away or more. It’s a bit like holding a magnifying glass to a magazine photo, you will see dots! but at 30cms, no dots.

A general rule of thumb; any image destined for on screen viewing should be 72 PPi (Pixels per inch). Anything for high quality print (brochures, books etc) should be 300 PPi.

All photographs © Jon Davison 2022.

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