We know the problem – you want to send a (hopefully) cleanly edited image for printing and look for suitable resharpening methods. So most people open a little sharpen filter and twist the radius until the picture is appropriately sharp. Of course, we know that you have to sharpen more for printing, so it rotates a little further than you would for screen playback.
Was everything done right? Probably not.
If you deal with images and retouching a lot, you will immediately recognize an over-sharpened image. Usually, it is the hair that is to dry, but also, the skin is increasingly suffering from over-sharpening.
The formula of happiness
Fortunately, there is a formula for printing that provides optimal sharpening!
The variables for sharpening
- r is the radius. Photoshop uses this variable, for example, when unsharp masking (also useable for sharpening in Capture One). It’s the aim to find this one out.
- For this, we first need the distance (d). This is the distance from which the image should usually be viewed. The unit is inches (remember: 1 inch corresponds to 2.54 centimeters).
- Furthermore, the resolution of the image is essential (res). The unit is dpi, i.e., dots per inch.
I want to improve my living room wall with a beautiful picture of a girl in the hedge, and of course, I want to achieve maximum sharpness. My couch is 4 meters away from this picture, and I sit there every day. This is my optimal viewing distance (4 meters = 157.48 inches). My picture is resolved with 240dpi, and this results in the following calculation:
The result – my optimal sharpening radius is 15.11808, meaning 15.1 – because Photoshop does not allow precise information.
This value is ingenious. But enjoy this value with caution, because it is based on the optimal print medium – and that doesn’t exist. On canvas or matte paper, you need experience or talk with your print contact person, because sometimes a higher or lower sharpening may be necessary. There are, therefore, methods in Photoshop, such as smart-objects or sharpening on separate levels for later adjustments, meaning full control.
Nevertheless, one thing stands out here: the size of the image is entirely irrelevant; only the viewing distance and the resolution per inch determine the sharpness.
Background information: What does the viewing distance have to do with it?
Well, the distance determines which details our eyes can still perceive in the distance. These details should, of course, correspond to the sharpness radius again.
By the way, if you don’t feel like filling out the formulas manually or even remembering them, you will find a practical calculator on this German website www.fineartprint.pro. The page is worth a bookmark.
The essence of this text comes from Paul Santek, the operator of the site mentioned – I had the pleasure of listening to a session of him at the BarCamp event, and I am pretty blown away by the topic of printing.
Did you miss last week’s blog article? Get more background information regarding sharpness here.
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