Resizing To The Printer Native Resolution

I received an email asking about my recent entries about PPI, DPI, and printer resolution. I was asked what this all has to do with printing since it is handled by the printer after depressing the print button. I haven't really discussed this yet and I think the missing link is the process of upsizing your image to the size you wish to print prior to printing. I'll discuss resizing in greater detail in a later entry, But I agree that it would help if I explained why since the printer does this automagicly.

All inkjet printers perform several stages of interpolation on a file before it is processed. The first stage is a resampling to the native printer resolution. I already mentioned in another blog entry that this is 360ppi on most Epson large format printers and 300ppi for most Canon and HP. This resampling process is fairly crude. By using Photoshop bicubic sharper or bucubic smoother you can do a much better job and see the results of the sharpening before printing. This is the main reason why it is better to interpolate to a native resolution before sending the data to the printer. The second processing stage is the ink dot placement algorithm which is a type of spatial filter. Since the dots in most new inkjet printers are smaller than the native pixel resolution of the printer this can result in very good interpolation, ( i.e. many dots make one pixel) but it can't correct for the defects introduced at the earlier stage.

By upsizing to the native printer resolution before printing, you can reduce the printer resampling in both stages ensuring better results. Usually the best improvements are found on edges, fine detail and tones.


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