Dr. I. D. Clever explains the DESKO world
Today: the world of resolution and line pairs
may I introduce myself? I am Dr. I. D. Clever and my task at DESKO is to explain things worth knowing about "document science" in a simple and understandable way.
- What is an identity document and what is not?
- How are identity documents structured?
- What technology is used to retrieve data from documents and how is it analyzed?
If these questions are relevant to your everyday work, then you've come to the right place. And if you are a non-specialist and want to impress with agent knowledge at the next boring stand-up reception, then you may also read on. Write to me, to which question in the matter of identity verification you are looking for an answer. Email me at email@example.com, keyword "Question for Dr. Clever" will do!
Your Dr. I. D. Clever
And so to our topic today:
What is actually understood by the term "resolution"?
Typically, when dealing with images and image-generating devices such as cameras or scanners, we talk about their resolution or resolution performance. But the term "resolution" is not as trivial as it might seem at first glance. The resolution of an image or device can mean different things. Basically, a distinction is made:
- Resolution as image dimensions: Height and width of the image in pixels.
- Resolution as pixel density of the image: The quotient of pixel / distance. The distance is usually measured in "inches" and thus the pixel density in "pixels per inch" (ppi or dpi).
- Resolution as a value for determining the quality of an optical system
Resolution as pixel density of an image file (dpi or ppi)
The units of measurement ppi or dpi indicate how many pixels can be imaged on one inch (2.54 cm). As a rule of thumb, the more pixels on a given distance, the higher the pixel density (resolution) and the more object details become visible.
Although the right image has a higher pixel density of 700 dpi, it looks much blurrier than the left image (pixel density of 500 dpi). The reason for this is that the quality of an image cannot be mapped with a single value such as pixel density. For example, the contrast behavior is also central when it comes to the quality of an image. If the contrast value is poor, the image will be blurred - even a high resolution in the sense of a high pixel density will not help.