0

I'm running Gimp 2.10.34

I know how to use Gaussian blur on images, but is there a non-destructive way to fade out or into a Gaussian blur, similar to using the gradient tool over a white layer mask?

I want the bottom of my image to remain sharp, and as you begin to look up, it shows more and more of the Gaussian blur.

Is this possible?

5 Answers 5

2

I would use GIMP's Focus Blur filter. It's not non-destructive, but you can create a layer from visible, and apply it to that layer, leaving your original layers unchanged.

Set it up like this.

enter image description hereClick to view larger

1
  • Feels like this tool was built for this very question. Thanks!
    – klewis
    Sep 30, 2023 at 21:47
2

Yes, you just stack a "sharp" version and "blurred" version, and add a layer mask with a gradient to unmask progressively the bottom picture:

enter image description here

1
  • Nice and Simple - Thanks!
    – klewis
    Sep 29, 2023 at 14:23
2

No need to change what's upvoted or accepted, but take some information:

Blending a sharp layer with its blurred copy with a gradient layer mask causes the sharp version gradually to fade behind the blurred version. In the transition zone the sharp version can still be seen as sharp behind the blurred version.

Someone may actually want totally different transition: A gradually growing blur radius like this:

enter image description here

When the blur becomes visible at certain distance from the image center, there's absolutely no ghost of the sharp version visible.

This effect is unfortunately destructive. As a workaround, keep a non-blurred backup copy of the original layer.

The effect is Lens Blur in G'MIC filter collection:

enter image description here

It's available for free to GIMP, Photoshop and Paint.NET. To Krita it's installed as a default.

To stay in truth GIMP and Photoshop both have working native Lens Blur effects. In Photoshop it can be controlled with layer mask and in GIMP it can be controlled with another layer. G'MIC version is much more handy if its controls are flexible enough for the intended purpose. GIMP has also "Variable Blur" which at first sight looks the same as GIMP's lens blur, but the programmers of the effects may somewhere reveal the difference. I have not seen it.

The effect is originally intended to simulate the blurring which happens in big cameras with wide lens aperture - only items which are in the relative shallow well focused distance range are imaged as sharp. Small format cameras do not have this property. Many photographers see it harmful, because automatically blurred background would effectively make the foreground target more present.

As a winding down here's another example of using the same filter:

enter image description here

1
  • very nice lesson! Thank you so much!
    – klewis
    Sep 29, 2023 at 23:24
2

Since the question is no longer about fading a Gaussian blur:

Gimp also has the Variable blur with which you can define a blur mask that tells how much the area should be blurred:

enter image description here

2

Here is another way to do it using layer masks.

  1. starting with your image: Original image of a record player

  2. Duplicate the layer

GIMP Duplicate Layer

  1. Now on that layer, ensure it is in front of the original layer, and add a Gaussian Blur to the entire layer.

Original image with a Guassian blur applied

  1. Click the Quick Mask button in the bottom corner (the image below shows the Quick Mask button just having been clicked, which displays as a solid red box).

GIMP Quick Mask Button

  1. Select the gradient tool, and make sure your foreground/background color is set to black and white:

GIMP Gradient tool and black and white color selection

  1. Draw a gradient across the layer in the direction you want the blur to appear

Image with a gradient layer mask added

Note that the red end will be the blurry end. You will see that there is not much fade on the left half of the image, because I want the blur to start just before halfway through the image, going left to right.

  1. Click the Quick Mask button again in the bottom corner to toggle the quick mask off (it will again show as a dotted box instead of a solid red box) and apply the mask to your layer. Once you do this, you will see that there is a selection applied to your layer

Image with GIMP Quick Mask Applied

  1. In the layers panel, ensure that your blurred layer has an Alpha channel. In the reference image below, I have already added the Alpha Channel, so it is greyed out. If it is not greyed out, that means there is no alpha channel, so you must add one.

GIMP Add Alpha Channel from Layer Panel

  1. Now press the DELETE button on your keyboard to delete what is selected (you may have to click back over to your main image window). You will now see a gradual transition from the original, non-blurred image to the newly blurred image. The selection will remain until you press Ctrl + A (Select All) to select the entire image.

Image with transitional Guassian blur applied

If you wish you, you can merge the blurred layer down.

You can try all sorts of different shapes of a gradient while the Quick Mask is toggled on to get different shapes for your blur transition. I did a linear fade in this example, but GIMP has many options for your gradient shape:

GIMP Gradient Tool Shape Options

1
  • Thanks for the lesson - nice job.
    – klewis
    Apr 8 at 16:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.