PPI, and DPI, what do they do?
Even those persons with just a nodding exposure to digital photography would have come across the terms PPI and DPI. Despite their ubiquity, considerable confusion exists on what exactly they mean.
This leads to their erroneous usage, frequently. Many wrong notions persist and unfortunately, people in the know – like photographic societies and many publications err by using one instead of the other, further complicating the issue. In this article, Smart Photography will give you the correct meaning of these in a simple way without resorting to complicated jargon.
The basic building block of an image is the picture element commonly known as the pixel. Each pixel is a square that can take any hue and shade but it is so small that a naked eye cannot see it individually. Once pixels are arranged properly as an array of rows and columns, your eye integrates them to form an image. If you open an image and enlarge it sufficiently with a suitable software package then you will be able to see individual pixels as discrete squares (Picture 1).
We often ask or speak about ‘image size’. What does that mean? Let us take an example of an image file that is 6000 (horizontal, H) and 4000 (vertical, V) pixels, or 24 megapixels (MP) in total. This image file cannot exist in a vacuum and has to be stored on a storage device like a hard disk. When you do so, it will occupy some storage space on the disk just as your book occupies some space on a shelf. This is specified in megabytes (MB). So, what does size refer to - size in pixels or size on
