What is DPI? Tell
DPI is a measurement of spatial print or density of video points that can be placed in a line within 1 inch (2.54 cm). Monitors do not have points, but they have pixels. A similar concept for monitors and images is pixels per inch or PPI. Many resources, including the Android Developer Guide, use the terms DPI and PPI interchangeably.
What is DPI in computer systems? This is an indicator of sharpness (density of the illuminated points) on the display screen. Dots per inch for a given resolution will differ depending on the overall screen size. Some users prefer the term “pixel per inch (PPI)” as a measure of image sharpness, retaining the DPI for use with print media.
What is DPI when printing? This is the number of dots per inch as an indicator of print quality on paper. The average personal computer printer today provides a resolution of 300 DPI or 600 DPI. Choosing a higher value usually reduces the speed of printing each page.
What is DPI? Measurement at the press
To a certain extent printers with a higher rate provide a clearer and more detailed output.A printer does not necessarily have a single DPI measurement. It depends on the print mode, which is affected by the driver settings.
The DPI range supported by the printer is most dependent on the print head technology used. So, a dot matrix printer, applies ink through tiny rods that damage ink ribbon, and has a relatively low DPI resolution, usually in the range of 60 to 90 (420 to 280 microns). An inkjet printer sprays ink through tiny nozzles and is usually capable of 300-720 DPI. A laser printer uses toner through a controlled electrostatic charge and can be in the range from 600 to 2400 DPI.
The DPI measurement for a printer often needs to be significantly higher than the measurement of pixels per inch (PPI) of a video display to provide an output of this quality. This is due to the limited range of colors for each DPI button normally available on the printer.
In each exact location, the simplest type of color printer can either print without a dot, or print a dot consisting of a fixed amount of ink in each of the four color channels (usually CMYK with cyan, magenta, yellow and black ink).
High-performance inkjet printers can offer 5, 6 or 7 ink colors, giving 32, 64 or 128 possible tones per spot.
Some color printers can create variable drop volumes at each point and can use additional color ink channels.
An exception to this rule are printers for sublimation of dyes, which can apply more of the latter, close to the number of 256 levels per channel available on a regular monitor, to each “pixel” on the page without smoothing, but with different restrictions:
Low spatial resolution (usually 200 to 300 dpi), which can make text and lines somewhat coarse.
Low output speed. One page requires three or four full passes, one for each color of the dye, each of which can take more than fifteen seconds, which is usually faster than the “photo” modes of most inkjet printers.
The uneconomic ink cartridge system.
Random color registration errors (mainly along the long axis of the page), which requires the printer to recalibrate to account for slippage and drift in the paper feed system.
These shortcomings mean that, despite their marked superiority in creating good photographic and non-linear graphic output, dye sublimation printers remain niche products, while devices with higher resolution, low color depth and smoothing patterns remain the norm.
What is DPI? Printing process
The printing process may require a range of four to six dots (measured across each side) to accurately reproduce the color in one pixel. An image that is 100 pixels wide may require from 400 to 600 dots wide in a printed output.
If the 100 × 100-pixel image needs to be printed in a one-inch square, the printer must have a resolution of 400 to 600 dpi to reproduce the image.
Accordingly, 600 DPI (sometimes 720) is today a typical output resolution for entry-level laser printers and some inkjet printers, with 1200/1440 and 2400/2880 being common “high” resolutions.
This contrasts with early 300/360 (or 240) dots per inch and an approximate 200 DPI for dot-matrix printers and fax machines that provide fax and computer-printed documents, especially those that used graphics or a color block.
DPI or PPI in digital image files
What is DPI, and how is it different from PPI? When printing, this figure refers to the output resolution of the printer or image processing device, and PPI (pixels per inch) refers to the input resolution of the photo or image.
DPI refers to the physical density of image points when it is reproduced as a real physical object, for example, printed on paper. The digital image does not have its own physical dimensions, measured in inches or centimeters.
Some digital file formats record the DPI value or, most often, the PPI value (pixels per inch) that should be used when printing. This allows the printer or software to know the size of the image or (in the case of scanned images) the size of the original scanned object. For example, a bitmap image can measure 1000 × 1000 pixels, a resolution of 1 megapixel.
If it is labeled 250 PPI, then this is the instruction for the printer to print it 4 × 4 inches. Changing the PPI to 100 in the image editing program will allow the printer to print it at a size of 10 × 10 inches.However, changing the PPI value would not change the image size in pixels, which would still be 1000 × 1000.
The image can also be reprocessed to change the number of pixels and, therefore, the size or resolution of the image.