Pixel Power - Perfect!

 

Anna's hummingbird showing why pixel count is important.

A pixel is an individual dot of colour. It does not have a particular size; that depends on how much an image is enlarged.  You can see in the above examples that the pixels in number 5 are much larger than that of number 4 and so on.  What's more important than pixel size is pixel count.  How many pixels there are.

Image number 1 is composed of almost a quarter of a million pixels.  We would call that 0.25 megapixels.  Although that seems like a lot, the truth is that modern cameras are capable of capturing 20 million or more pixels.  Although we rarely need that many pixels when working with a photo, the advantage is that we can significantly crop it as a means of enlarging the photo.  Cutting out 75% of the original image still leaves 5 megapixels which are still enough to do quite a bit with.

You may have noticed that each iteration represents a reduction in pixel count by a factor of 4.  That is because I shrunk each shot by 50%.  If that doesn't make sense to you, consider an 8x10 reduced to a 4x5.  An 8x10 has an area of 80 square inches while the 4x5 has only 20.  Half the dimensions, a quarter of the area.  Also, notice that the pixel size increases as the pixel counts get smaller.  The original images (left side) all have pixels the same size which is why the shots become progressively smaller while the enlarged images (right side) are all the same size but then need larger pixels to facilitate that. 

How many pixels are enough?  The answer to that question is another question.  What do you want to do with the image?  Viewing a shot on a cell phone requires fewer pixels than viewing it on a computer.  Making a print of an image requires even more than that, especially if enlargements are made.  A 4x6 print should have around 2 million pixels.  An 8x10 requires 7 million, and a 16x20 print may use over 25 million pixels.  The 4x6 viewed on a computer, cell phone, or other device needs less than 0.25 megapixels.

The conclusion then is to consider what you want to do with an image.  Going to keep it only for computer use?  No cropping required?  A small pixel count under 1 megapixel is fine.  Want to crop something heavily?  Make an enlargement?  Better to start off with 20 or 25 megapixels and then whittle that down as needed.  You can make a decent 8x10 print by taking a 25-megapixel image and doing a 75% crop.  Pixel count is especially important to consider when sharing files with others.  Ask what their purpose is and you will know what to do.  

Thanks for reading.   

Eric Svendsen      www.ericspix.com