Welcome to the first part of our series that aims to help you improve the experience of printing photos using an ink-jet printer
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You've printed some photos on your home printer but you want more. The colour, the clarity – they could be better, so what's the way forward? This multi-part tutorial aims to bring people who want to improve their photo printing to the next level. We'll help you to understand the technology behind ink-jet printing, but without drowning you in technical jargon. Today, we examine the fundamentals.
Introduction
It's important to know how your printer works so you can understand how better quality prints can be achieved. This series focuses on ink-jet printers, which are by far the most widely available photo printer type for home use. Today we're going to examine how ink turns into photos, telling apart pixels and dots and finding out why different types of printer paper produce such wildly different results.
Dots and pixels
No dots, no photo prints. No pixels, no image to print. Although dots and pixels are widely confused, as far as DPNow is concerned, dots are the bits of colour laid down by a printer to make the print and pixels are the fundamental electronic 'picture elements' of a digital image. One image pixel may be represented on a print by several dots of different coloured ink.
On the left is a twelve megapixel original image. On the right is the portion of the image indicated by the coloured area on the left.
See the smaller area highlighted on the right. That's what's represented in the images a bit further down this page.
A printer depends on the accurate placing millions of different coloured microscopic droplets of ink onto the surface of the paper to form the photographic image. Each ink droplet forms a printed dot. The paper surface is very important, too, as we will find later. As we have already hinted, several printed dots represent one picture element, or image pixel. So how many printer dots do we need to represent one image pixel? At this stage, don't worry about it. This will be addressed in a later tutorial that deals with printer driver settings. But what we can address today is the number of image pixels that will be reproduced in a given space on the paper.
Here you can see the original image pixels that form this tiny area of the overall image.
Printing can be a rather inexact science and ideal image to print resolution is certainly not exact. The generally accepted rule of thumb is that you should aim for at least 300 image pixels to be reproduced along an inch of print, or 300 pixels per inch (ppi). Let's say your image has 2,500 horizontal pixels. At 300ppi, you would have an ideal printed resolution in a print 8.3 inches wide (2500 divided by 300). In reality, you can get away with less than 300 pixels per printed inch, especially if the print is a large on and the viewing distance isn't too close. The quality of the image makes a big difference too; great quality pixels can withstand being blown up much better than those in average or poor quality images.
And here are the printer dots from a print of the image; it's the same area as that in the image above showing the images pixels.
The white areas in the mid-right are specks of dust on the print.
Recap
Pixels are the electronic picture elements that make up a digital image.
Dots are the spots of colour that are laid down as ink droplets by the printer.
One image pixel is represented on a printed photo by several printer dots.
Around 300 image pixels reproduced per inch of photo print (300ppi) is considered an ideal minimum.
Print resolution
It's worth noting that the image resolution assumptions here are based on original images. If you resize an image, you might change the quality that the image is capable of delivering once printed.
You may have seen image attributes like 72 or 96 ppi (or even confusingly referred to as 'dpi). These numbers are much lower than the ideal minimum of 300ppi. Prints at, say 72ppi, would not look very good. Much of the time, you can ignore these figures. When a photo is printed by an application, like a photo editing software package (Photoshop, for example) the software automatically fits the image to the printed size chosen by you, regardless of the preset resolution.
Now try this
At the end of each part of this series there will be a simple practical exercise to for you to do. It's not compulsory, but it will help you to crystallise some of the points made.
This time, we have two photo images you can download and print. Print them out to a size of 6x4 inches and study then carefully. Each image is from the same original, but one is sized for ideal (300ppi) photo print reproduction and the other is only screen resolution (72ppi) pixels, or 432x288 pixels. You should be able to see a marked difference in printed quality.
Click to download and print this 72ppi sample image.
Click to download and print this 300ppi sample image.
And don't forget, if you have any questions about this article, you can post a question on the DPNow forum (see the latest posts at the end of this page), though forum registration is required if you are not already registered in order to post.
Next time
In part 2 of this series we look at inks and papers and find out why the choice of both is vital for both print quality and resistance to fading.
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