1. Resolution of the scan

a) Scan a design

		paper design			scan			digital design

The characteristics of a paper design are its height and its width in inch or in centimeters, and the continuous lines that build the design.

Scanning a paper design means translating the same height and width in a digital language, i.e. the design is translated into pixels.

		Paper design, continuous lines			Digital design, pixels

b) Pixels

A pixel is a digital notion. On the screen three photophores represent one pixel. A red, a green and a blue photophore build an aluminous point or one in color. Each of this pixel has a code to specify the color, for example 255 for black.

c) Resolution

Scanning a paper design means translating the continuous lines on a grid of pixels.

			width in inch				width in pixels
	height in inch								height in pixel

The resolution fixes the number of dots per inch.

When you choose a resolution to scan a paper design, you decide the number of points that will represent the paper design on the screen.

The bigger the resolution is, the more point it will use, the more precisely the scan will be.

Example of different resolutions

paper design width and height

scan at 45 dpi

scan at 90 dpi

scan at 180 dpi

In the scans (digital design) you keep the same width and height as in the paper design, it is just the number of dots per inch that various, the higher the resolution the more precisely the digital design will be, but the more memory it will need.


d) Resolution in cm

Example scanned at 180 dpi

	1 inch =2,54 cm
								180 dpi
					180 dpi

Convert the resolution of dpi in dots per cm;

	1 inch 2,54 cm 1 cm		180 dots 180 dots 180/2,54 = 70,87 dots

A resolution of 70,87 dots per cm is an equivalent of 180 dpi.

To convert a resolution measurement of dots per inch into, dots per cm you divide the dpi by 2,54cm. 1 inch equals 2,54 cm.

2. Changing resolution

a) changing resolution of the digital design

If you want to keep the original size of the design you need to leave the design at the same resolution as you scanned it, so when you print it remains the same.

scanned at: 1 inch =180 dots
left at: 180 dots = 1 inch
new design: 180 dots/ 180dots = 1 inch

If you change the resolution of the design before you print it.
scanned at: 1 inch = 180 dots
changed to: 360 dots = 1 inch
new design: 180 dots/ 360 dots = 0,5 inch

The design will be half the size of the original.

width in pixels

360 dpi

width in pixels

width in inch

180 dpi

paper design

digital design in pixelsprinted design in the new resolution

b) Resolution of the printer

One pixel produced by a printer is build out of different points of color, cyan, magenta, yellow, black. Each printer has a choice of different resolutions, which can not be modified and various from printer to printer.

The resolution of a digital design should be a multiple of the printer resolution.

• Design at 360 dpi , printer resolution at 360 dpi

	digital design at 360 dpi		printed with a resolution of 360 dpi

When the resolution of the digital design is the same as the resolution of the printer, each pixel corresponds to one point of the printer.

• Design at 180 dpi, printer resolution at 360 dpi

	digital design at 180 dpi		printed with a resolution of 360 dpi

When the resolution of the digital design is half the size of the resolution of the printer, each pixel corresponds to two points in the width and two points in the height (4 points) of the printer. The size of the design will remain the same.

• Design at 120 dpi , printer resolution at 360 dpi

	digital design at 120 dpi		printed with a resolution of 360 dpi

When the resolution of the digital design is three times smaller than the resolution of the printer, each pixel corresponds to three points in the width and three points in the height (9 points) of the printer. The size of the design will remain the same.

• Design at 720 dpi , printer resolution at 360 dpi

			printed with a resolution of 360 dpi
	digital design at 720 dpi

When the resolution of the digital design is twice as big as the resolution of the printer, two pixels corresponds to one point in the width and one point in the height (1 point) of the printer. This can cause quality loss. The size of the design will remain the same.

• Design at 140 dpi , printer resolution at 360 dpi

	digital design at 140 dpi				printed at a resolution of 360 dpi

When the resolution of the digital design is 1,50 times smaller than the resolution of the printer, one pixel will have a random size. Sometimes two points in the width and height and sometimes one point in the two directions of the printer. This can cause quality loss. The size of the design will remain the same.

3. Conclusion

To get a high quality print, the resolution of you digital design has to be a multiple of your printer resolution. If you use a printer resolution of 720 dpi, your design should have a resolution of 360, 180, 90 or 60 dpi.

To get a good result, choose a multiple of the printer resolution before you scan. This allows keeping the original size of the design. (see 2.a)

If you scan at a resolution of 720 or 360 dpi, you will have a very high quality scan, but a very heavy one too. A design like this will take a lot of memory, which can slow down the computer.