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Pixels and Dots

PPI and DPI ' they sound the same but are they??? The short answer is NO!

PPI stands for 'Pixels Per Inch' and DPI for 'Dots Per Inch' ' so a pixel is not a dot. Pixels relate to digital images as seen on your monitor and captured in your camera. Dots relate to the droplets of ink your printer spits out of the print head and its ability to print those images in detail.

Colour photographs are printed using four basic colours, Cyan, Magenta, Yellow, and Black (CMYK), and separate dot patterns for each ink. Our Canon printers use 12 different colours - Matte Black, Photo Black, Grey, Photo Grey, Magenta, Photo Magenta, Cyan, Photo Cyan, Yellow, Red, Green and Blue - ensuring the widest colour gamut and best possible results.

Printer resolution is given as the number of 'dots per inch' (dpi). DPI is the maximum number of ink dots that the printer is capable of placing on your paper per inch. Photo-quality ink-jet printers spray ink through multiple nozzles to produce various sized droplets with variable droplet spacing. When the droplets are sprayed onto paper the drops overlap, combine, or are spaced so as to reproduce the colour of the individual pixel being printed. The printer may have to spray a drop of all six colours on top of each other to generate a dark colour. In other words, it takes multiple drops of ink from the printer to create the colour in each square pixel. So even if the printer resolution is given as 1200dpi it does not mean that there are 1200dots lined up in a row in each inch of the print. Believe it or not, the printer's resolution numbers have nothing to do with the size of, or the number of pixels in your image.

72ppi V 300ppi

All digital images are made up of tiny squares called pixels, and each pixel in your image has a specific size and a specific colour value. The size of your pixels is determined by the resolution of your image and is actually inversely proportional to resolution. In a 24-bit (RGB) colour image, there are 256 possible shades of red, green, and blue mixed to represent the colour of each pixel. 256 shades of red, green, and blue can be combined to produce a total of 16.7 million different colours. 16.7 million colours are sufficient for photo-realistic output. It requires 3 bytes of information to record and store the colour of each pixel, and therefore the file size of an RGB image will be approximately three times the pixel size.

The resolution of your ink-jet printer has absolutely nothing to do with the image resolution. When printing images on an ink-jet printer, images should be sized for your desired print size (length and height), and that the resolution should be set at 200-300 pixels per inch. Images with resolutions set much below 200ppi will be of inferior quality because the pixels start to become visible. There is no advantage in sending an image with a resolution greater than 300ppi to your ink-jet printer. If you are printing to a different type of device, check with your lab (or the manual for the specific device) to determine the appropriate output resolution. You are unlikely to be able to perceive the difference between an ink-jet prints made at 200ppi versus 300ppi without a magnifying glass. Images destined for e-mail or the web should have a resolution of 72ppi because this matches the resolution of most monitors on which the images are likely to be viewed.

The majority of digital cameras will capture an image as 72 or 300PPI. Most desktop and wide format digital printers operate at 600, 720, 1440, 1200 or 1800DPI. We print our images typically at 1200 x 1200DPI which gives great photo quality when dealing with reasonable quality digital files.

The chart below compares the print size that comes from most digital cameras today. Our 1200megapixel Custom Copy Camera is listed at the bottom for comparison also.

Megapixels versus Maximum Ideal Print Size.

 Megapixels Pixel Resolution
File Size
 Print size @ 300ppi
Print Size @ 200ppi
Print Size @ 72ppi
 3
 2048 x 1536
 9mb 17.3 x 13cm
6.82" x 5.12"
26 x 19.5cm
10.24" x 7.68"
72.3 x 54.2cm
28.45" x 21.33"
 4  2464 x 1632
 11.5mb  20.9 x 13.8cm
8.21" x 5.44"
31.3 x 20.7cm
12.32" x 8.16"
86.9 x 57.6cm
34.22" x 22.67"
 6  3008 x 2000
 17.2mb  25.5 x 16.9cm
10.02" x 6.67"
38.2 x 25.4cm
15.04" x 10"
106.1 x 70.6cm
41.78" x 27.78"
 8  3264 x 2448
 22.9mb  27.6 x 20.7cm
10.88" x 8.16"
41.5 x 31.1cm
16.32" x 12.24"
115.1 x 86.4cm
45.33" x 34"
 10  3872 x 2592  28.7mb  32.8 x 21.9cm
12.91" x 8.64"
49.2 x 32.9cm
19.36" x 12.96"
136.6 x 91.4cm
53.78" x 36"
 12  4290 x 2800  34.4mb  36.3 x 23.7cm
14.3" x 9.34"
54.5 x 35.6cm
21.45" x 14"
151.3 x 98.8cm
59.58" x 38.89"
 16  4920 x 3264  45.9mb  41.7 x 27.6cm
16.4" x 10.88"
62.5 x 41.5cm
24.6" x 16.32"
173.6 x 83.3cm
68.33" x 45.33"
 Our 1200 megapixel
Copy Camera
 20000 x 20000  1,120mb
or 1.2GB
169 x 169cm
66.7" x 66.7"
Bigger than we can print  

*Typical Resolution. Actual pixel dimensions vary from camera to camera.
**At 72ppi, printed images will have visible pixels and details will look "fuzzy" in most sizes.

We have at our disposal a variety of tools which allows us to enlarge these images far beyond those sizes listed above. So while we might only have a small 3megapixel file to work with, we can often take this far larger than the sizes listed above.

Viewing distance changes everything!
Have you ever looked closely at the printing on the side of a bus? These images are usually very low PPI and printed at very low dpi to get them that large. The thing is that when you watch them drive by the images look great but up close you can play 'Join the Dots'!

Everything is relative to viewing distance. A 300PPI file from an 8megapixel camera sized at 20 x 25cm and printed as a 20 x 25cm photograph and viewed at arm's length will look as good as the bus does from 20 metres but it will get better the closer you get. Take that same image and interpolate it up to 100 x 80cm and view it from 2-3 metres and it will look just as good as the small one but get up close to it and you will see pixilation.