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Review the scanning techniques graphics professionals and photographers use, while delving into workflow considerations and the advanced image-quality controls available in most scanning software. Author Taz Tally explains the core concepts, such as how resolution and interpolation affect scans; introduces the industry-standard SilverFast scanning software; and shares the settings to achieve the best results from a scan. The course also covers keeping your scanner and its parts clean and free of dust, and includes a variety of start-to-finish scanning tasks.
Let's discuss setting your scan resolution. This topic can get a little bit confusing and one of the reasons as we've discussed earlier is that there is different terminologies, different ways of looking at in expressing resolution. We're going to run into a little bit of that here, but hopefully we can square things around and clear it up. First of all let's talk about setting resolution for a continuous tone image and then we'll address line art separately. The first point to make about setting Scan Resolution is that there is two things that we're going to use to determine Scan Resolution or Input Resolution.
That is, Scanning Resolution is dependent upon the output device and on scaling, those are the two variables. For instance some output device if we go to like the web for instance, 72 pixels per inch is still the standard, all that may rise over time. I'll put resolution for desktop printers 200 pixels per inch. For high quality inkjet printers 240 pixels per inch is at this point in time we found out to be that kind of an optimal resolution for high-quality, photographic quality of inkjets. For commercial printing, typically between 200 and 300 pixels per inch depending upon the printing press and something called Line Screen, which we're going to get to right now.
So before we go any further with that description of output device and scaling let's take a side-trip into a little bit of terminology. First to understand that all the expertise, the greater expertise behind SilverFast scanning software really comes from Prepress which is why it's such a great software, because Prepress has always been kind of the gold standard for image quality. And one of the results of that is some of the terminology from Prepress is used in some of these dialog boxes. Things like this you see in the word Densitometer which is a Prepress term.
In Photoshop we call that the Info panel. They do the same thing they are just different terms, when we run into some of the same issues when we talk about resolution. When we look at resolution and setting resolution in SilverFast this is the area of the SilverFast panel that we use for setting resolution. You'll notice that there is a variable called Q-Factor and something called Screen, and it gives you megabytes which is file size and then there is dpi down here. Let's address these terminologies and kind of square those round with what we've been talking about.
First let's do the dpi. dpi has been used in Prepress forever, but really this is pixels print. That's the terminology that we're using. We're using image resolution technology based upon the building blocks and since we're creating pixel-based images we're using pixels per inch, and you can click here and you can change this to dots per centimeter if you want to if you're a centimeter-type person. Instead of using dot it's pixels. So that's the first thing. Second thing is lpi, this is definitely a Prepress term, and you can use lpi or lines per centimeter and the L stands for Lines and what the lines refers to is the number of lines of halftone dots that are laid down in every single inch or centimeter.
One of the standards in Prepress is 150 lpi or lines per inch. Now the one who is 175 is commonly used. For newspaper printing it may be 80 or 100 lines per inch. It's the number of rows of halftone dots in every linear inch. Scanning resolution is based upon the requirements of the output device, while in commercial printing since we're using patterns of conventional half-tone dots we use that variable, that factor to help us determine what the input scan resolution could be, and that's what the Q-Factor is all about.
It's a relationship of pixels per inch to line screen, and typically for commercial printing this number is going to be anywhere from 1.5 to 2.0 times a line screen and for the various highest quality commercial printing generally it's going to be two times the line screen. So the pixels print then if we 2 times the line screen gives us 300 pixels per inch. If I adjust this to 1.5 times a line screen, notice it drops it down to 225, so the really good news here is that SilverFast is doing the math for you, and this is handy to use this Q-Factor at first if it's new it's a little bit confusing, but let me show you another reason why this is a nifty dialog box to use when we talk about scaling, but let me finish this discussion.
So if you're using Q-Factor and we're talking about continuous tone images here, SilverFast is going to do all the math for you. If you're unsure to use 1.5 or 2.0, error on the side of more pixels rather than fewer, although if you have too many pixels it is going to be down-sampled when you go to Press, but it's better to have a little bit too many than not enough, because having to sample up when you're printing creates far more deleterious impact on your quality of your images to sampling down a little bit. In the best of all possible world you scan it at exactly the resolution that which you're going to print.
Most of us don't do that, we tend to take our images and use them in multiple places, we use them for commercial printing, desktop printing, send them to the newspaper and use them around the webpage. And if you, like me and most people are multipurpose in your images then what we do is we scan for the highest quality device and then we can make copies of those images and down-sample them for using our own five different devices if we'd scan it five different times, well, sorry that's going to cut into my kayaking time way too much. So I am going to scan it once for the highest quality device and then make copies and down-sample it.
Soon the highest quality image is going to be two times a line screen that would mean a 300 pixel per inch scan. Now let's go back and discuss this scaling, remember we set our 4.0x5.0 inch frame and then we wanted to actually I'll put it at 8.0x10.0, so we have a scaling factor of 200. The good news is we have a 200% scale let's say, we absolutely want the scaling to occur, the scanner is going to work with original data information. If we just do 100% scale take it into Photoshop and then scale it up there using Photoshop Interpolation, will end up with far lower quality images.
This is one of those times we want to let the scanner do the scaling. So 200 pixels per inch times the 300, we really should be scanning at 600 pixels per inch. If you press your Ctrl key it shows you the actual optical resolution which your image is going to be scanned, when you release it goes to 300 which gives you this math times the 200, it actually makes the determination for you. So it's great, once you understand what the Q-Factor is all about and Line Screen all you have to do is put in the Scaling, put in your Q-Factor of 1.5 to 2.0 and you can discuss this with your printing company, you go to standard printing company that you normally work with and they may tell you, oh! 1.5 is fine and for a lot of printing it is fine, so you can choose your factor there.
But the nice news is that SilverFast will do all the scaling for you and all the mathematics for you which is great, so that's for continuous tone images. Now for line art, when I'm scanning line art, one, I don't usually scale my line art during my scan at all and particularly simple line art, and the reason for this is that I don't want any interpolation occur along that edge. Remember we talked about that edge quality and we want to minimize the amount of interpolation. If I've got simple line art I am going to be converting that into vectors and then doing my scaling.
So for line art I put my Q-Factor at 1. 0, and then I just set my independent resolution right here. For scaling line art I always start with 100% up here and then I just set Q-Factor of 0 so there is no multiplication, and then as you'll see I typically use either 600 pixels per inch for simple line art that I am converting to vectors or 1200 pixels per inch if I'm keeping my image as a pixel-based line art image. So I am going to get nice high detail, sharp edges, and I can reproduce detailed lined art images.
There setting your resolution, it's probably going to be worthwhile to go through this a couple of times and listen to it, but you're really going to get it when you start actually scanning your own images and scaling them up and then I am going to refer you to the simple and detailed line art scanning portions of this course where I show you specifically in the details why we want scan at 6 and 1200 and we don't want the scanner to do the scaling.
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