Printer Resolution Confusion


Today’s Question: As you mentioned, most inkjet printers use a print resolution of around 360 ppi [pixels per inch]. I always set my output resolution at 360 ppi with good results.  However the specs for my printer, a Canon Pixma MP610 state a print resolution of 600 x 600 for mono and 9600 x 2400 for color. So what am I missing? Is the true resolution (from a photo printing standpoint) different from the manufacturers stated output resolution?

Tim’s Quick Answer: The confusion here relates to the pixel resolution of the image compared to the number of ink droplets put down on paper by the printer. Put simply, multiple droplets of ink are required to produce a single pixel from your photo when printing an image.

More Detail: A typical printer that makes use of the 360 pixel per inch output resolution I’ve referred to in prior editions of the Ask Tim Grey eNewsletter. However, more than one droplet of ink is required to reproduce each pixel in the original image. For example, with a printer that employs seven different ink colors, if one droplet of ink were used for each pixel in the image, you could only have seven total possible color values in the image.

Instead, printers use tiny droplets of ink and combine multiple droplets to reproduce each (also very small) pixel in the image you’re printing. In many cases the individual droplets of ink also vary in size based on the specific color being reproduced for a given pixel in the printed image.

As noted in today’s question, printer manufacturers generally present the number of droplets the printer can place in a linear inch when referring to the resolution of the printer, rather than referencing the underlying pixel per inch resolution that would be optimal for the source image you are printing.

The resolution based on the number of droplets of ink does provide a relative indication of potential image quality and potential color range that the printer can reproduce. So in general a higher value is beneficial, up to a point. But you don’t need to use that resolution based on ink droplets when preparing your photo for printing. Most printers today, for example, render your image data at a resolution of somewhere between about 300 pixels per inch and 720 pixels per inch. That differs from typical ink droplet resolutions of around 1,440 to around 3,000 or more droplets of ink.

The primary source of confusion, of course, is that both the number of pixels in the source image and the number of droplets of ink used to reproduce pixels on paper are described in terms of pixels per inch. But in these two cases the definition of “pixels” actually differs.