November 5, 2018
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Creating a digital file for digital printing is very much like creating a digital file that is going to be displayed on a monitor as a web page or a PDF or JPG – with a few very important differences. In order to help ensure the highest quality of your printed materials, this article offers a useful set of practices for you to follow, from how to set your color space, to bleeds, to resolution. Part 3 demonstrates how to sharpen digital images to prepare them for digital printing.
We also have Tip Sheets available on color conversion, file resolution, bleeds, and how to set up your digital files in various programs. You can find them all on the Printing Tips page of our website.
Photoshop has a complete suite of tools to help with enhancing photos. Colors can be saturated or adjusted, contrast can be increased or decreased, and the sharpness of the image can be improved. There isn’t time in this article to go over all the elements of color and contrast correction, but let’s take a look at sharpening, since it’s one of the best ways to help a so-so photo look better – including a photo that you needed to enlarge. We’ll quickly go over three methods.
Photos taken directly from your smartphone camera, digital camera, or off a scanner, are usually not as sharp as you would like. While some digital cameras offer sharpening, you have very little to no control over the method and amount. Or perhaps you do some capture sharpening in LightRoom. You will still want to sharpen photos in Photoshop to achieve good crisp printed images. That said, there are limits to how much you can improve a photo with sharpening; if it’s a blurry photo to begin with, you can make it better but it will never be as good as starting out with a clear, well-focused photo.
In Photoshop, under Filter, find the submenu for Sharpen. There are a lot of options, mainly because Photoshop likes to add functions, but seems to hate deleting old ones – it’s a hoarder program. The first three – sharpen, sharpen edge, sharpen more – are easy but imprecise. We’ll go over Smart Sharpen, Unsharp mask and a third method that isn’t found in the Sharpen submenu.
No matter which form of sharpening you use, it’s best to perform this operation last, and to save a separate file after you have sharpened. That’s because sharpening needs differ depending on the final usage of the photos (for instance, online or printing) and cannot be undone. Some people insist on sharpening in a separate layer and setting that layer on Luminosity to help avoid unwanted color shifts or colored halos that sometimes occur in sharpening. Also, you can vary the opacity of the second layer to effect the amount of sharpening, giving you one more degree of control.
One of the skills you’ll develop as you sharpen more images for printing is to determine how much sharpening is enough. Images that are sharpened enough for printing often look too sharp on your monitor, often making you cringe and back off on the sharpening. The result may be photos that appear under-sharpened on paper. Unfortunately, there’s no accurate way to make sure that your digital image is sharpened enough – or over-sharpened – for printing except trial and error, and experience. It’s a good idea to check your printed pieces against the sharpened images on your monitor to get a feel for the correspondence between the two. A good rule of thumb is that images that look slightly over-sharpened on screen are about right for printing.
Unsharp Masking is a weird name for a filter that sharpens, but it describes the process pretty well. When you choose it Photoshop creates a blurred image of your photo, compares it to the original and subtracts the differences, in effect masking the non-sharp edges in the photo. What makes Unsharp Masking a more precise tool is that it gives you three controls.
Amount lets you set how much contrast you want to add at those edges; in effect, how much sharpening you want.
Radius affects the size of the edges that you are sharpening. A larger radius will tend to look sharper, but you have to be careful because it can also create unwanted “halos,” or detectable rims around objects.
Threshold tells the software the amount of tonal difference between pixels to look for before sharpening the pixel. So the lower the threshold the more pixels that are affected. For instance, set the threshold at 8 and all pixels with tonal values that differ by 8 or more will be sharpened. So too low of a threshold may sharpen individual grains, or even noise, making a photo look grainy. Too high won’t sharpen enough. The beauty of Unsharp Masking is that all three tools interact, giving you a lot of flexibility to address the needs of different photos.
Smart Sharpening also gives you a lot of control and adds an element of “deconvolution” to the sharpening process – a fancy way of saying that you can ameliorate the effects of an earlier Gaussian, Lens, or Motion blur, to a point. Motion blur can be used to help correct for slight camera movement. As with Unsharp Mask, Smart Masking gives you control over the amount and radius, though not the threshold. Click on Advanced and it lets you vary the amount of sharpening in the shadows and highlights by fading the sharpening in either, and extending or decreasing the tonal values to extend or limit the tonal ranges to be sharpened.
High Pass Sharpening is a great, creative way to sharpen that offers a lot of control and tends to avoid halos and other artifacts. To use it, first create a duplicate layer of your photo, then select that layer and go to Filter > Other > High Pass. You will get an option to set the radius – usually between 1 and 3 works well, but you can experiment with different photos. With preview turned on you’ll see your photo turn gray and look a little bit 3D. Click OK and the fun begins. Now you can blend the two layers in different ways to achieve different levels of sharpening. Start with Overlay, but also try Soft Light, Hard Light, Vivid Light and Liner Light – the sharpening effect will increase as you move down this list. You can also effect the amount of sharpening by varying the Opacity between the layers. Have fun.
We’re digital printing experts serving the Portland, Oregon area and the U.S. For more information, check out our website at: https://www.rhinodigital.com. Or better yet, give us a call at: 503-233-2477. We’ll be happy to answer all your questions and help you with tips and information on getting your printing projects done in the most economical and timely manner possible.