Question Scanning resolution question

[mikeymikec]

As I understand it, scanners can scan natively up to a certain resolution (in dpi), and beyond that resolution they do what's called interpolation (which I personally define as "adding pretend content"). My Epson WF-3520 AIO printer according to the specs has a scanning resolution of 1200x2400dpi. Does that mean the "real" max scanning setting is 1200dpi?

 

[Paperdoc]

From what I can see, yes. The way their specs read you CAN get "higher" resolutions achieved by interpolation, but those all appear to be multiples of 1200 dpi.

I looked up the "subscan" resolution spec of 2400 dpi to see what that means. Best explanation I found, which makes sense, is that the sensor array is 1200 dpi across the sheet, while the mechanism that moves that array strip along the page can grab sample lines at a spacing of 2400 dpi down the length of the page. In the older view of "square" resolution specs, I'd call that a 1200 dpi scanner. That is surely VERY good and more than most users might ever need. Professional photographers and some graphics art pros might need more for some projects, but not most of us.

 

[Steltek]

From what I can see, yes. The way their specs read you CAN get "higher" resolutions achieved by interpolation, but those all appear to be multiples of 1200 dpi.

I looked up the "subscan" resolution spec of 2400 dpi to see what that means. Best explanation I found, which makes sense, is that the sensor array is 1200 dpi across the sheet, while the mechanism that moves that array strip along the page can grab sample lines at a spacing of 2400 dpi down the length of the page. In the older view of "square" resolution specs, I'd call that a 1200 dpi scanner. That is surely VERY good and more than most users might ever need. Professional photographers and some graphics art pros might need more for some projects, but not most of us.

This is correct. The optical resolution of your scanner is 1200dpi.

The hardware resolution is shown as 1200x2400dpi (i.e. horizontal x vertical) because the stepper motor Epson used in it double-steps the CCD carriage while scanning vertically, which doubles the vertical scan resolution. The horizontal scan resolution is the short side across the rectangular scan bed, the vertical scan resolution is the long side down the rectangular scan bed.

There are some scanners actually quadruple-step the CCD carriage vertically so you get 4 times the vertical scan resolution.

Photography wise, you aren't on the high end (I think the old Epson 4990 photo scanner I had about 15 years ago was optically rated at 4800dpi) but it still ought to be very decent for the majority of photographs you might scan with it.

For most everything else, 1200dpi will likely be overkill as 300dpi for web and 600dpi for most other things will suffice (and allow you to avoid the expense of dealing with gigabytes of scans).

 

[mindless1]

It is an inexpensive AIO, probably using CIS type scan engine, so it's more than just the true resolution that is the limitation.

When quality matters, (then you're out of luck but...) you might want to scan at twice the (horizontal) resolution you want, then edit/touch-up if needed, then downsample it. I mean 1200DPI or lower, no point in having it extrapolate to higher horiz. than 1200DPI.

Then again, considering low end CIS best use case is scanning B&W documents, not color reproduction or 3D field of focus, if the lower resolution is "good enough", you don't need the extra step of downsampling, and if the higher DPI setting is more than its buffer and USB transport can handle in realtime so it is moving the sensor backwards, then forward again along the scan bed to compensate, that can degrade quality as well.

 

[dave_the_nerd]

FWIW, even 600dpi is plenty if you're just scanning text. Depending on what you do with the scanner, the max optical resolution might not even matter.