Dots per inch (DPI) is a measure of spatial printing or video resolution, in particular the number of individual dots or pixels within the span of one linear inch (2. Printing is a process for reproducing text and image typically with ink on Paper using a printing press Video is the technology of electronically capturing, Recording, processing storing transmitting and reconstructing a sequence of Still images In Digital imaging, a pixel ( pict ure el ement is the smallest piece of information in an image Inches redirects here To see the Les Savy Fav album see Inches. 54 cm. A centimetre ( American spelling: centimeter, symbol cm) is a unit of Length in the Metric system, equal to one hundredth )

A close-up of the dots produced by an inkjet printer at draft quality. Inkjet printers operate by propelling variably-sized droplets of liquid or molten material ( Ink) onto almost any sized page Actual size is approximately 0. 25 inches square (. 635 square centimetres). Individual coloured droplets of ink are visible; this sample is about 150 DPI.

DPI measurement in video resolution

Because color display units use three coloured sub-pixels (red, green and blue) per pixel, the DPI measurement is frequently misused, especially in the automotive market. Video is the technology of electronically capturing, Recording, processing storing transmitting and reconstructing a sequence of Still images In Digital imaging, a pixel ( pict ure el ement is the smallest piece of information in an image An example of misuse would be if an LCD monitor manufacturer claimed that a 320x240 pixel 3" monitor (2. 4"x1. 8") actually had a resolution of 400 DPI, (three times the pixels per inch). Technically this would be correct (as each sub-pixel could be considered a dot), but compared to the standard accepted practice of using pixels as a means of measuring resolution, it could mislead customers into thinking the relabeled monitor had a greater resolution and therefore better picture quality than identical but normally labeled monitors. Such misuse is commonly found in advertising for in-car LCD displays.

A less misleading term, therefore, is pixels per inch. Video displays are almost universally rated in dot pitch, which refers to the spacing between the sub-pixel red, green and blue dots which make up the pixels themselves. Dot pitch (sometimes called line pitch, phosphor pitch or pixel pitch) is a specification for a Computer display, Computer printer Very often, DPI is confused with image size, leading to expressions such as "1024 x 768 DPI XGA. "

DPI measurement in printing

Up to a point, printers with higher DPI produce clearer and more detailed output. A printer does not necessarily have a single DPI measurement; it is dependent on print mode, which is usually influenced by driver settings. The range of DPI supported by a printer is most dependent on the print head technology it uses. A dot matrix printer, for example, applies ink via tiny rods striking an ink ribbon, and has a relatively low resolution, typically in the range of 60 to 90 DPI. A dot matrix printer or impact matrix printer refers to a type of Computer printer with a print head that runs back and forth on the page and prints by impact striking An inkjet printer sprays ink through tiny nozzles, and is typically capable of 300-600 DPI. Inkjet printers operate by propelling variably-sized droplets of liquid or molten material ( Ink) onto almost any sized page ^[1] A laser printer applies toner through a controlled electrostatic charge, and may be in the range of 600 to 1800 DPI. A laser printer is a common type of Computer printer that rapidly produces high quality text and graphics on plain paper For the Irish surname see Toner (surname. Toner is a powder used in Laser printers and Photocopiers to form

The DPI measurement of a printer often needs to be considerably higher than the pixels per inch (PPI) measurement of a video display in order to produce similar-quality output. This is due to the limited range of colours for each dot typically available on a printer. At each dot position, the simplest type of colour printer can print no dot, or a dot consisting of a fixed volume of ink in each of four colour channels (typically CMYK with cyan, magenta, yellow and black ink). CMYK (short for '''c'''yan, '''m'''agenta, '''y'''ellow, and k ey ( Black) and often referred to as process color Cyan (saɪæn from Greek κυανός / kyanos, meaning "blue" may be used as the name of any of a number of a range of colors in the blue/green part of Magenta is a purplish red Color evoked by lights with less power in yellowish-green Wavelengths than in blue and red wavelengths ( complements of magenta have Yellow is the Color evoked by light that stimulates both the L and M (long and medium wavelength Cone cells of the Retina about equally Black is the Color of objects that do not emit or Reflect Light in any part of the Visible spectrum; they absorb all such frequencies of Contrast this to a standard sRGB monitor where each pixel produces 256 intensities of light in each of three channels (RGB) to additively create 256³ = 16,777,216 colours. sRGB is a standard RGB (Red Green Blue color space created cooperatively by HP and Microsoft for use on monitors printers and the Internet An additive color model involves Light emitted directly from a source or illuminant of some sort The number of unique colours for a printed CMYK dot from this simplest type of inkjet printer is only 8 since no coloured ink is visible when printed on black and black is used instead of CMY:

• white (no ink)
• cyan
• magenta
• yellow
• blue = cyan + magenta
• green = cyan + yellow
• red = magenta+yellow
• dark brown (not used) = cyan + magenta + yellow
• black

While some colour printers can produce variable drop volumes at each dot position, and may use additional ink colour channels, the number of colours is still typically less than on a monitor. White is a Color, the perception which is evoked by Light that stimulates all three types of color sensitive Cone cells in the Human eye Cyan (saɪæn from Greek κυανός / kyanos, meaning "blue" may be used as the name of any of a number of a range of colors in the blue/green part of Magenta is a purplish red Color evoked by lights with less power in yellowish-green Wavelengths than in blue and red wavelengths ( complements of magenta have Yellow is the Color evoked by light that stimulates both the L and M (long and medium wavelength Cone cells of the Retina about equally Blue is a Colour, the Perception of which is evoked by Green is a Color, the perception of which is evoked by light having a spectrum dominated by energy with a Wavelength of roughly 520–570- nm. Red is any of a number of similar Colors evoked by light consisting predominantly of the longest wavelengths of Light discernible by the human eye in the wavelength Black, when used as a general term is a color that is a Very dark Black, black, or Black, of low Luminance relative to Black is the Color of objects that do not emit or Reflect Light in any part of the Visible spectrum; they absorb all such frequencies of Most printers must therefore produce additional colours through a halftone or dithering process. Halftone is the Reprographic technique that simulates Continuous tone imagery through the use of equally spaced dots of varying size Dither is an intentionally applied form of Noise, used to randomize Quantization error, thereby preventing large-scale patterns such as contouring that are more objectionable The exception to this rule is a Dye-sublimation printer that utilizes a printing method more akin to Pixels per inch. A dye-sublimation printer (or dye-sub printer) is a Computer printer which employs a printing process that uses heat to transfer dye to a medium such as a plastic

The printing process could require a region from four to six dots (measured across each side) in order to faithfully reproduce the colour contained in a single pixel. An image that is 100 pixels wide may need to be 400 to 600 dots in width in the printed output; if a 100×100-pixel image is to be printed inside a one-inch square, the printer must be capable of 400 to 600 dots per inch in order to accurately reproduce the image.

A 10×10-pixel image on a computer display usually requires many more than 10×10 printer dots to accurately reproduce, due to limitations of available ink colours in the printer.

DPI in digital image files

DPI refers to the physical size of an image when it is reproduced as a real physical entity, for example printed onto paper, or displayed on a monitor. A digitally stored image has no inherent physical dimensions, measured in inches or centimetres. Some digital file formats record a DPI value, which is to be used when printing the image. This number lets the printer know the intended size of the image, or in the case of scanned images, the size of the original scanned object. For example, a bitmap image may measure 1000×1000 pixels, a resolution of one megapixel. In Computer graphics, a bitmap or pixmap is a type of memory organization or Image file format used to store Digital images The In Digital imaging, a pixel ( pict ure el ement is the smallest piece of information in an image If it is labeled as 250 DPI, that is an instruction to the printer to print it at a size of 4×4 inches. Changing the DPI to 100 in an image editing program would tell the printer to print it at a size of 10×10 inches. However, changing the DPI value would not change the size of the image in pixels which would still be 1000×1000. An image may also be resampled to change the number of pixels and therefore the size or resolution of the image, but this is quite different from simply setting a new DPI for the file.

For vector images, there is no equivalent of resampling an image when it is resized, and there is no DPI in the file because it is resolution independent (prints equally well at all sizes). Vector graphics is the use of geometrical primitives such as points lines, Curves and shapes or Polygon (s which are all based However there is still a target printing size. Some image formats, such as Photoshop format, can contain both bitmap and vector data in the same file. Adjusting the DPI in a Photoshop file will change the intended printing size of the bitmap portion of the data and also change the intended printing size of the vector data to match. This way the vector and bitmap data maintain a consistent size relationship when the target printing size is changed. Text stored as outline fonts in bitmap image formats is handled in the same way. Other formats, such as PDF, are primarily vector formats which can have bitmaps pasted into them. In these formats the target DPI of the bitmaps is adjusted to match when the target print size of the file is changed. This is the converse of how it works in a primarily bitmap format like Photoshop, but has exactly the same result of maintaining the relationship between the vector and bitmap portions of the data.

Proposed metrification

There are some ongoing efforts to abandon DPI in favour of giving the inter-dot spacing in micrometres (µm). Metrication (or metrification refers to the introduction of the SI metric system as the International standard for physical measurements—a long-term series A micrometre ( American spelling: micrometer; symbol µm) is one millionth of a Metre, or equivalently one thousandth of a Millimetre A resolution of 72 DPI for example equals an inter-dot spacing of about 350 µm, 96 DPI → 265 µm, 160 DPI 160 µm, 300 DPI → 85 µm, 4000 DPI → 6. 4 µm. Going the other way, 1 µm → 25400 DPI, 30 µm → 850 DPI, 200 µm → 127 DPI. Note that 25400 = 1 DPI·µm, so dividing 25400 by a measurement in one of these units gives the measurement in the other unit.

Some have also proposed using “dots per centimetre” (DPCM). ^[2]

See also

• Pixels per inch
• Samples per inch
• Lines per inch
• Metric typographic units
• Display resolution
• Mouse DPI

References

External links

• All About Digital Photos - The Myth of DPI