- Digital Image Processing
- DIP - Home
- DIP - Image Processing Introduction
- DIP - Signal and System Introduction
- DIP - History of Photography
- DIP - Applications and Usage
- DIP - Concept of Dimensions
- DIP - Image Formation on Camera
- DIP - Camera Mechanism
- DIP - Concept of Pixel
- DIP - Perspective Transformation
- DIP - Concept of Bits Per Pixel
- DIP - Types of Images
- DIP - Color Codes Conversion
- DIP - Grayscale to RGB Conversion
- DIP - Concept of Sampling
- DIP - Pixel Resolution
- DIP - Concept of Zooming
- DIP - Zooming methods
- DIP - Spatial Resolution
- DIP - Pixels Dots and Lines per inch
- DIP - Gray Level Resolution
- DIP - Concept of Quantization
- DIP - ISO Preference curves
- DIP - Concept of Dithering
- DIP - Histograms Introduction
- DIP - Brightness and Contrast
- DIP - Image Transformations
- DIP - Histogram Sliding
- DIP - Histogram Stretching
- DIP - Introduction to Probability
- DIP - Histogram Equalization
- DIP - Gray Level Transformations
- DIP - Concept of convolution
- DIP - Concept of Masks
- DIP - Concept of Blurring
- DIP - Concept of Edge Detection
- DIP - Prewitt Operator
- DIP - Sobel operator
- DIP - Robinson Compass Mask
- DIP - Krisch Compass Mask
- DIP - Laplacian Operator
- DIP - Frequency Domain Analysis
- DIP - Fourier series and Transform
- DIP - Convolution theorm
- DIP - High Pass vs Low Pass Filters
- DIP - Introduction to Color Spaces
- DIP - JPEG compression
- DIP - Optical Character Recognition
- DIP - Computer Vision and Graphics
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
Pixels, Dots and Lines Per Inch
In the previous tutorial of spatial resolution , we discussed the brief introduction of PPI, DPI, LPI. Now we are formally going to discuss all of them.
Pixels per inch
Pixel density or Pixels per inch is a measure of spatial resolution for different devices that includes tablets, mobile phones.
The higher is the PPI, the higher is the quality. In order to more understand it, that how it calculated. Lets calculate the PPI of a mobile phone.
Calculating pixels per inch (PPI) of Samsung galaxy S4:
The Samsung galaxy s4 has PPI or pixel density of 441. But how does it is calculated?
First of all we will Pythagoras theorem to calculate the diagonal resolution in pixels.
It can be given as:
Where a and b are the height and width resolutions in pixel and c is the diagonal resolution in pixels.
For Samsung galaxy s4, it is 1080 x 1920 pixels.
So putting those values in the equation gives the result
C = 2202.90717
Now we will calculate PPI
PPI = c / diagonal size in inches
The diagonal size in inches of Samsung galaxy s4 is 5.0 inches , which can be confirmed from anywhere.
PPI = 2202.90717/5.0
PPI = 440.58
PPI = 441 (approx)
That means that the pixel density of Samsung galaxy s4 is 441 PPI.
Dots per inch.
The dpi is often relate to PPI, whereas there is a difference between these two. DPI or dots per inch is a measure of spatial resolution of printers. In case of printers, dpi means that how many dots of ink are printed per inch when an image get printed out from the printer.
Remember, it is not necessary that each Pixel per inch is printed by one dot per inch. There may be many dots per inch used for printing one pixel. The reason behind this that most of the color printers uses CMYK model. The colors are limited. Printer has to choose from these colors to make the color of the pixel whereas within pc, you have hundreds of thousands of colors.
The higher is the dpi of the printer, the higher is the quality of the printed document or image on paper.
Usually some of the laser printers have dpi of 300 and some have 600 or more.
Lines per inch
When dpi refers to dots per inch, liner per inch refers to lines of dots per inch. The resolution of halftone screen is measured in lines per inch.
The following table shows some of the lines per inch capacity of the printers.
|Screen printing||45-65 lpi|
|Laser printer (300 dpi)||65 lpi|
|Laser printer (600 dpi)||85-105 lpi|
|Offset Press (newsprint paper)||85 lpi|
|Offset Press (coated paper)||85-185 lpi|