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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.
Here I'd like to address some of the tools and processes for removing patterns inside of images that we're about to scan, and in particular, I'd like to address the challenge of removing halftone dot patterns from printed images. Images like this, and this was from a book from the 1920s, it's got all sorts of problems. It's low contrast and there's lots of shadow detail has been lost and high light detail has been lost, but the most significant problem here is if we magnify this, we see what this image is made up of. It's a previously printed image in a relatively coarse lined screen, somewhere between probably 80 and 100 line screen on this book and that's what the image is really made up of, is these black and white dots from which the image was originally printed.
When you scan printed image like this at standard continuous tone image resolutions for a scanner like 200 to 300 pixels/inch, it definitely picks up that halftone dot pattern. So what we want to do is to try to remove that pattern, not only because this look bad, but if we try to reprint this already printed image, it's creates what's called a moray pattern, because this dot pattern interferes with the dot pattern that's being used in the current printing device. It gets ugly in a hurry, so we need to remove this if we can. Let's put this image away for a second. Now let's go on over to the SilverFast interface and see what we can do here.
First, I've done a preview scan and I've set my frame on that image and first thing we'll do is adjust the brightness and contrast and set highlights and shadows, but in images like this that are nothing but dot pattern basically, I don't try to do a numeric setting of the highlights and shadows. I still use this tool with the levels, but basically I use the histogram as my guide for setting highlights and shadows in this image, and I just drag the highlight over to just the beginning and if you watch this image over here, you see, dramatically improves the overall brightness and contrast of the image and I'll do the same thing on the shadow end, just so that the data starts to bump up.
Be little careful in the shadow end on these kind images, just move it over so you start to get that data, because most of the shadow data is filled in, anyway, no sense making it worse, and then we can click OK and it's perfectly fine to come up here and add a little bit of brightness to the overall image. That's no problem, using the Curve Gradation tool. Then we're going to the Descreening filter, which is underneath the Filter menu here, and this de-screening filter works in this fashion. We are going to do a couple of things. First of all if you know what the screen pattern is, you can set that LPI, the Lines Per Inch and I'm not really sure what it is here.
I think it's between 85 and 100, so I'm going to do a detect screen, and then I'm going to click Prescan, and you'll notice nothing happens, but don't be frustrated and keep clicking Prescan. What Prescan does is it produces this little rectangle that you then move over the image to select the area where you would like the prescan to occur. Now you could click up here, now let's go ahead and do that and see the result and you get an idea of how this technology works. And what SilverFast does is on the left it shows you the not de-screened image, that is the patterned image, and on the right it shows you the de-screened version.
It worked pretty darn well, looks good, doesn't it? But that's probably not the most effective place to really click on the Prescan, a better area to click is something like this where you've got some detail, and I'm going to click here, because not only does it show some edge detail, but there is also a pattern in the basket that I want to monitor while I go through this process as well. Pretty good, and look at the line screen. It tells us it's 106, and we're pretty close. All right, we can just stop there if we want to, but there are some other things we can do here, that's going to give you a pretty good quality image. And we could go down here to Adaptation and Sensitivity, but I've used this dialog box enough that, what I tend to do is this, and you can make up your own method if you like.
you're fine, after you get some practice. I like to turn on my use Unsharp Masking, this is the Unsharp Masking tool that we talked about in the previous movie. Now watch this image as I click on, Use Unsharp Mask. Do you see how it sharpens up. It actually shows you a preview of what's about to happen. It's fairly cool. What's important about using Unsharp Mask is the danger of using too much of it, because remember what sharpening does, is increase edge contrast between adjacent pixels. And remember this original image was black-and-white pixels. So if you would have sharpened for instance, the not Descreen version, it would just make matters worse.
If you apply to much sharpening, it can maybe bring back that pattern, so I'm very careful, but I would like it to be a little bit sharper, if I can. So typically with the images like this, I'll keep this at about 50%, keep my Threshold at 1, you can play with the Oversharpen, you can drag this all the way over if you want and you can see the impact on the screen up here with no sharpening and then over sharpening, you can drag this all the way up to 100%. And what's nice here is the light and the dark contour. I'd leave that at 50%, particularly with images like this, because what it does is it progressively decreases the amount of sharpening as you get close to real, real high contrast edges.
So it's a very sophisticated tool and it works very well. Rather than going directly to these tools, I really try to use Unsharp Mask, and let me just zoom in here. I want to go up just a little bit, because I want to show you something. Notice if we go with Retain edges, and Retain edges is another type of edge sharpening tool. If I turn this on notice what happens to these edges, do you see how they start to get a little bit to Oversharpened and particularly if we drag these over here, and particularly if we do the Retain Text portion, which make it even sharper, and notice that we could, in this image we could take and include the text here, and we could zoom in on the text and take a look at it.
But my experience teaches me that I generally don't use this as much as I use the combination of the Descreening and then the Unsharp Mask and I tend to get pretty darn good results when I do that. There are some other details you can set here, you can set the matrix, I've had very good luck using the 3x3 matrix you can choose a 5x5 or x7, experiment with various kinds of images, because there' all sorts of different kinds of screened in pattern images. There is also an expert mode here that you can get into and out of, we have been in the expert mode that allows us to control the light and dark contours and I like to work with the Oversharpened and then setting the light and dark and contours, so that we don't get super amount of sharpening along that real high contrast light and dark edges, so there we go.
So we're going to do a combination of Descreening and then Sharpening and it's going to occur in that order, and that's particularly important how you want to do that. And then we're ready to scan our image and we're going to call this -- we'll just call this a DSS, which is Descreened and Sharpened and then I'm going to show you some variations on these scans that I've already created. All right so what SilverFast does now is it captures the image and it kind of shows you onscreen as it goes through it. Scans it to the file and you can see the halftone dot pattern very clearly, and then it goes through it's descreening process, and there we have it.
Let's bring this up and compare it to our original image. Not too bad, got rid of all that halftone dot pattern, and image like this, a descreened image, it's a very, very poor quality to begin with. It's never going to have the kind of sharpness that you have in a regular scan from continuous tone image, but you're going to be able to print this and it's not going to have that horrible moray pattern that going to be created when you try to print an image like you can see in the background over here. All right, so there is descreening plus sharpening through SilverFast.
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