Why Pixel Size Matters
September 9, 2007
Thanks to the marketing of retailers and manufacturers, consumers have been led to believe that more pixels equates to higher image quality. With more pixels consumers are left with the option to crop images tighter on a computer to compensate for the shorter focal length lenses typical of point and shoot cameras. However, new point and shoots still won’t produce as high quality of an image as those produced from a professional or consumer grade DSLR with the same number of pixels. Lens quality has an effect, but sensor size is the key factor here.
A single frame of 35mm film measures 36mm x 24mm. A digital sensor with those dimensions is called “full frame”. There are only a few pro-level cameras (currently $3000 to $8000) that contain this size sensor. A more common sensor size found in many consumer level DSLRs is 22.5mm x 15mm (with slight variations), referred to as APS-C, with prices ranging approximately $700 to $1500. Point and shoot cameras have a range of sensor sizes with many commonly around 7mm x 5mm, about the size of a small fingernail.
The following image shows the relative sizes of three 8mp Canon camera sensors.
Because all three cameras have 8 megapixels it’s obvious that individual pixels on the point and shoot SD850 sensor are drastically smaller in comparison to the pixels on the professional 1D mkll DSLR and consumer grade 20D DSLR sensors.
So why is image quality better on cameras with larger pixels?
To create a print an image captured on a smaller sensor needs to be enlarged more than an image captured on a larger sensor with the same number of pixels. In short, the smaller pixels get “stretched out” a lot more. But there are more benefits to having larger pixels than just the amount of “stretching”.
Larger pixels have more surface area for gathering light, resulting in each pixel capturing a wider dynamic range (information between light and dark). This is because more possible variations of light can be collected before the pixel reaches maximum capacity. The image captured will contain more detail in transitions between light and dark areas and will contain less digital noise than an image captured on a smaller sensor with the same number of pixels.
For more in depth information on dynamic range and digital noise please refer to the following articles found on dpreview.com:
