Inkjet print resolution

<p>I have a question. Since I bought my new printer I've done a lot of searching all over the net about the correct print resolution as measured in PPI. I've found many interesting articles, studies, discussions, suggestions, ... most of them condivisible and enlightening... I've even thought of doing my own tests but I gave up, first of all I needed a perfect image and looking at my portfolio I had none. I've learned that a resolution between 240 and 300 ppi is good enough, that for Epson printers 360 ppi is maybe the best possible, and that 180 ppi is ok but not so good or even scarce. So my question is: if you send a file at 180 ppi to your printer and your printer prints it without messing things up, that means it has to print 180x180=32,400 pixels per square inch, or 50 pixels per square millimeter. Since a pixel does have a color, I should be able to recognize 50 different shades of color inside a square millimeter before I could say that 180 ppi is not a good resolution.</p>

<p>Keith Cooper wrote this a while back............</p>

<p>http://www.northlight-images.co.uk/article_pages/print_viewing_distance.html</p>

<p>In the traditional darkroom the printing paper resolution was usually the weakest link and getting high resolution was aided by printing larger rather than smaller, the limitation then being the ability of the negative resolution to go that extra distance.</p>

<p>I am curious, incited by your question, to ask what the resolution of the inkjet papers is in electronic printing? I have not printed a lot numerically and usually abide by the 300 ppi rule of thumb, but what if the paper itself cannot resolve very much? Is it necessary to stick to 300 ppi or another high resolution of the file (300 ppi, determined of course for the desired print output size)?</p>

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<p>I've learned that a resolution between 240 and 300 ppi is good enough, that for Epson printers 360 ppi is maybe the best possible, and that 180 ppi is ok but not so good or even scarce.d</p>

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<p>Here's what Epson recommends (we** taught this at the Epson Print Academy):<br>

Figure out what size you want the print to be (8x10, 13x19 etc). In Photoshop examine what the PPI values are at the size you desire. <strong>IF</strong> they fall between 180ppi and 480ppi, you're done. Just send that to the printer. Doesn't matter if the value is 181, 345, 258 (any odd value that falls between the 180-480 recommendation). <br>

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** Jeff Schewe, Mac Holbert, JP Caponigro, Greg Gorman and myself</p>

<p>First of all, thanks to Andrew Rodney for clarifying that business about what resolution one has to send to the printer. I've been in a lot of disagreements about this one and am happy to be in the group that agrees that it doesn't matter.</p>

<p>I'll add two things. The first is that many top printers will tell you that they can see resolution increase up to about 720. That doesn't mean everyone can, certainly not non-photographers with untrained eyes. Jon Cone made a chart a few years ago regarding b&w printing that showed some very incredible capacity. Here, at the bottom of the page: <a id="">http://shopping.netsuite.com/s.nl/c.362672/it.I/id.119/.f?sc=15&category=27707#</a><br>

I figure anything over 300 is good, there is good print quality. I like 400 better, but that's just my eyes. I don't believe in image distance. Everyone looks up close.</p>

<p>The other thing I would add is that one has to be careful in thinking about what one is actually looking at. For the first while when I got my first drum scanner, back in 2002, I struggled to understand what I was actually looking at - when I zoomed in to 200% in PhotoShop. Were these grains? Did the scanner take a snapshot of the sampling spot? The answer to both was, of course, No. The scanner scans a sample spot, gets a number, and that's what you see. It's a strange mental construct, or it was for me until I understood. Photoshop is a math program more than anything.</p>

<p>By the same token, a printer does not print the pixels in the image directly. Bear in mind how the piezoelectric chip works. A piezo chip sits on top of a very small reservoir of ink close to the paper. When a small electric charge is applied the chip oscillates wildly and ink gets spit out thru the tiny holes in the head below. This is very different from taking the square pixel from Photoshop and somehow printing it as if it were a very small image. The pixel has a set of numbers associated with it for the cmyk values and the chips gets a specific amount of voltage based on those values, they send droplets of ink to the paper in an attempt to create something analogous to the original pixel, or group of pixels. Given the small sizes of everything, somehow it all comes together to create an image. However, when you look at a print with a 10x loupe you seek a bunch of tiny droplets of ink. They are only partially related to the original image. (By math.)</p>

<p>I'm hoping this will help you answer your question.</p>

 

<p>For an Epson, I prefer to resize in an editor to the desired print size at 360 dpi and do any final editing and sharpening. Saving this file simplifies any future printing.</p>

<p>Thank you all for the valuable input. I think I'll stick to the 180/480 <em>rule</em> (thanks Andrew). Of course I am well aware that making a good print it's far more complex than just counting pixels, so I'd welcome any suggestion about good books (I'm not in the US so classes are out of question). Thanks.</p>

<p>I'm with Jim Jones, and at least there's no indication here that this would do any harm.</p>

<p>I use a RIP, so its a little different for me. It cares nothing for how many pixels I send it. In the case of Epson's driver, if one takes a minute to understand what is happening, you will have to assume that Andrew is right. A number of highly regarded experts (in addition to Andrew) agree with him, which ought to be enough to convince people. You'd think at least one of them might have stuck a piece of paper in a printer to test this before they went against conventional wisdom. I'm sure they did.</p>

<p>I've disagreed with Andrew on a point or two. We have different experiences in the real world, different ways we use Photoshop. It's not that one can't disagree, but I think the dismissive tone is a bit much here. These are all serious people who think about this stuff all day long and constantly test their assumptions.</p>

<p>However, let's look at the technical part of this. We all work in either RGB or Grayscale. Let's ignore the latter for a moment for purposes of discussion. The printers do not work in RGB at all, they do their work in CMYK. Epson has software which converts RGB to CMYK, using a combination of your image's profile and a tremendous amount of sophisticated math. In speaking to the techs from the RIP I use, they explained that it works in at least 5 "dimensions." It considers a color space, a profile, a point to point conversion, a set of curves to place colors not identified in the profile in the right place - in three dimensions, etc. Do you think after all this that the software in the printer is going to choke on images that do not have an exact number of pixels? I would say that it would be silly to assume so. This is very complicated stuff, they aren't going to get stuck on whether there ought to be 300, 360 or 363 pixels. The 363 number was actually a real statement, if one can imagine, it came from a guy that taught a lot of workshops, that I have very little respect for - he appears to be all hot air. </p>

<p>As to the statement "Saving this file simplifies any future printing." This is entirely false. If a flattened and sharpened image prints exactly the same months from now as it did today, then one simply isn't looking very closely. As temperature and humidity change the absorption rate of the coating will differ. I haven't ever just pressed print one more time (months later) and handed it to someone as a finished product. For one's family snapshots, sure. However, not for a top quality print of any sort.</p>

<p>There is a way to simplify things in the future. That's to have a series of adjustment layers with their masks on them. Then you can simply adjust a little up or down on each layer to get the print to where you want it.</p>

<p>Hope this is helpful.</p>