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Tag : Sharpening

sharpening for billboards

Resharpening for printing

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!

general formula for resharpening

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.

An Example

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:

formula for resharpening example

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.

Do you have any suggestions, additions, is this post out of date, or have you found any mistakes? Then we look forward to your comment.
You are welcome to share this post. We are very grateful for every recommendation.

Photo by ROMBO from Pexels

The concept of sharpness

You see them again and again, totally over-sharpened images. Funny Jesus halos were created, hair looks super dry, and somehow everything becomes cheap again.

What is sharpness?

Sharpness is in contrast. The contrast in the form of differences in brightness at edges and details – but also color contrast or saturation contrast. Yes – even the image content can affect image sharpness.

Adobe Photoshop looks for edges when sharpening them and makes them lighter on one side and darker on the other. Photoshop has no idea of color contrasts.
Photoshop can only make luminance contrasts:

scharpen_01scharpen_02

Let’s take a closer look and do the same thing again:

scharpen_03

scharpen_04

Pay attention to the eye – that’s nice and sharp in this image – unfortunately, the skin texture suffered from it, the hair is strawy, and the hands “glow”.

But for luminance processing, there is an excellent, manual tool: Dodge & Burn. So here the ” manually sharpened “version:

scharpen_05scharpen_06

In this example, too, the eye is sharp – and there are no side effects. Incidentally, this took almost 2 minutes.

Sharpness through color contrasts

Let’s take a look at this image here:

scharpen_07

The two colors are very similar – the red and the orange differ only by a small offset in color. Saturation and luminance are the same. If we now change one of those color fields in hue (but leave the saturation and luminance the same), this is the result:

scharpen_08

The separation between the two fields is so strong that even JPG compression reaches its limits and shows artifacts in the middle. The contrast is extreme here – only by changing the color tone.

Transferred to an image, you could apply it as follows:scharpen_09scharpen_10

Here the color tone was changed only minimally, and a sharper image emerged. A very subtle effect – again without side effects.

Conclusion

If you want to have sharp images, you can keep the contrasts and contrast edges in mind when retouching – this usually makes subsequent sharpening obsolete. At Dodge & Burn, I always try to darken the edges a few percents more and lightly lighten the other side of the edge. When it comes to colors, I pay attention to the color harmonies, so that you automatically achieve very harmonious, but at the same time, sharp contrasts.

A little hint at the end

If you sharpen while using the raw converter (meaning before retouching) or pull the saturation upwards, you will get a sharper picture, but in the end, you do twice the work. All of the problems highlighted by this global sharpening also want to be eliminated again. It is better to use the raw conversion for a somewhat flatter but balanced image and to increase the sharpness in the image during retouching deliberately.

Stay tuned for the next blog article regarding sharpness in the upcoming week.

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Do you have any suggestions, additions, is this post out of date, or have you found any mistakes? Then we look forward to your comment.
You are welcome to share this post. We are very grateful for every recommendation.