A constant source of confusion is the terms being used.

Printer resolution and image resolution are two different things.

Printer resolution is expressed in DPI. 9600 X 2400 DPI is the printer resolution. The first term (9600) is very important when looking at resolution, whereas the second number (2400) is critical for higest quality as it refers to how the ink jet head actually pus the ink droplets down in the second dimension of printing. Since printing makes a 2 dimensional print, the second number fills in the ink in the second direction. 9600X2400 is your printers maximum quality, uses the most ink, and takes the longest amount of time. You can print at lower printer resolutions to increase the speed of your print and also save ink. There does come a point, however, where the quality of the print will deteriorate and be unacceptable. Normally, you will select the quality of the print in your printer settings when you select the paper type and quality setting.

Image resolution has 2 components: ppi and size. It is meaningless to know the number of pixels per inch (ppi) without also knowing the image dimensions. It’s kind of like saying someone went on a trip at 70mph. Without knowing the travel time or distance, 70 mph has no reference point. Digital cameras (or scans) use pixel width and height to refer to image resolution. For example, a 6mpix camera has a maximum image size of 3072 X 2048 pixels (total area of just over 6,000,000 pixels). It is important to note that none of this refers to printer resolution. Image resolution is about the number of pixels in the digital file; printer resolution is about putting dots of ink down on paper.

To adjust the image size and/or resolution, you open the image size dialogue box in your editing software program. Uncheck “Resample” (Resampling will change the resolution by adding or subtracting pixels to increase or decrease the size of a photo — avoid resampling whenever you can). With resampling unchecked, you can change the ppi setting to any number you wish and you are not changing the number of pixels of the image. If you started with 3072X2048, you still have 6meg whether it is at 72 ppi or 300 ppi. But remember what ppi refers to — pixels PER INCH. If you divide the number of pixels available by the ppi, you’ll know the size of the print AT THAT RESOLUTION. 3072X2048 @ 300 ppi will give you a print of 10.24 inches X 6.84 inches. The same print at 200 ppi would give you a print size of 15.4 inches X 10.24 inches. The key here is that fewer pixels will be printed for each inch of print you choose. There comes a point where that becomes a quality issue and you begin to see degradation in your print because the pixels are larger and become visible.

While I’m on the subject, ppi has no meaning on the web. You can set your ppi to any value you want and it will look the same on your monitor because the monitor is more interested in the number of pixels not the inches of the image.

In most instances, a 300 ppi image will print just fine but a lower value will allow you to print larger images without resampling. Typically, you should print in the 200-300 ppi range. Lower than that will result in print degradation and larger than that is generally not noticible to even the most discerning eye and just uses more ink and can actually cause your printer to fail is you chose very high image resolutions. Choosing the value depends on the size of the print you are going to print.

This brings us to the point of what happens if I want to print a print that is larger than I can get without resampling? Well, you can allow the software to resample the image and add pixels to the image, thus making the image larger. As you can imagine, the more you resample, the more “extra” pixels are added, the lower the quality. A good image resampling program/method is critical to quality prints when you start adding pixels.