Pixel and DPI, picture size and resolution
Pixel
A pixel is the smallest element of a digital picture. Pixel is the abbreviation of "picture element".
Simply, pixels are rectangular points on the screen, all of which form the whole picture like a mosaic.
The real size of a pixel is not always the same; it depends from the monitor and its resolution.
The colour of each pixel on the monitor is a mixture of the three basic colours red, green and blue.
A picture resolution of 640 x 480 pixels means therefore, that each row of the whole picture consists of 640 horizontal and each column of 480 vertical picture elements.
So all in all the picture consists of 307.200 pixels.
The higher the number of pixels, the better the picture quality
The quality of a picture depends on ist resolution.
The higher the number of pixels, the better and sharper will be the print and the presentation on the monitor.
What means DPI ?
DPI means dots per inch and plays an important role in printing.
The higher this number, the "nearer together" are the picture elements (pixels) on the paper: the printing so gets sharper and more detailed, but at the same time smaller in dimensions.
Therefore if you want to print in high quality and in large dimensions, you need an adequate high number of pixels.
Following are some examples.
Examples of calculation
Example 1
Print of a picture with 2048 x 3072 pixels and 300 dpi:
2048 pixels/300 = 6,83 inch; the picture width in printing is therefore 6,83 inch
3072 pixels/300 = 10,24 inch; the picture height in printing is therefore 10,24 inch
Example 2
Print of a picture with 2048 x 3072 pixels and 72 dpi:
2048 pixels/72 = 28,44 inch; the picture width in printing is therefore 28,44 inch
3072 pixels/72 = 42,67 inch; the picture height in printing is therefore 42,67 inch
Tabelle 1: Definition of the picture quality dependent on the resolution
Resolution in dpi |
Quality |
< 100 dpi |
very bad |
100 - 150 dpi |
moderate |
150 - 200 dpi |
average |
200 - 300 dpi |
good |
> 300 dpi |
optimal |
Chart 2: Connection of picture resolution, picture size and picture quality (jpg-format)
Resolution (pixel) |
Megapixel |
Picture size (inch) |
6 x 4 (DIN A6) |
8 x 6 (DIN A5) |
12 x 8 (DIN A4) |
16 x 12 (DIN A3) |
640 x 480 |
0,3 |
moderate |
very bad |
very bad |
very bad |
1024 x 768 |
0,8 |
average |
moderate |
very bad |
very bad |
1600 x 1200 |
1,9 |
good |
average |
moderate |
moderate |
2048 x 1600 |
3,2 |
optimal |
good |
average |
moderate |
2560 x 1920 |
5,0 |
optimal |
good |
good |
average |
3008 x 2000 |
6,0 |
optimal |
optimal |
good |
average |
3264 x 2448 |
8,0 |
optimal |
optimal |
good |
good |
3648 x 2736 |
10,0 |
optimal |
optimal |
optimal |
good |
4000 x 3000 |
12,0 |
optimal |
optimal |
optimal |
good |
4752 x 3168 |
15,0 |
optimal |
optimal |
optimal |
optimal |