How to Create Frosted Glass Effect in GIMP

The frosted glass (or glassmorphism) effect is a popular modern design trend that creates a semi-transparent, blurred overlay with subtle borders and shadows over a background image. This guide provides a straightforward, step-by-step walkthrough to help you design a realistic frosted glass blur overlay in GIMP using duplicate layers, Gaussian blur, layer masks, and highlight borders.

Step 1: Open Your Image and Duplicate the Background

  1. Open GIMP and load your background image via File > Open.
  2. Go to the Layers panel on the right.
  3. Right-click your background layer and select Duplicate Layer (or press Shift + Ctrl + D).
  4. Rename this duplicate layer to Blurred Background.

Step 2: Apply the Blur Effect

  1. Select the Blurred Background layer in the Layers panel.
  2. Navigate to Filters > Blur > Gaussian Blur...
  3. In the dialog, set both the Size X and Size Y values to a high amount (typically between 25.0 and 50.0, depending on the resolution of your image).
  4. Click OK to apply the blur.

Step 3: Define the Glass Overlay Shape

  1. Choose the Rectangle Select Tool (R) from the toolbox (or the Rounded Rectangle option by checking "Rounded corners" in the tool options).
  2. Draw the shape of your glass card over the area where you want the frosted overlay to appear.
  3. With the selection active, right-click the Blurred Background layer and select Add Layer Mask.
  4. In the dialog, choose Selection and click Add.
  5. Clear the active selection by going to Select > None (Shift + Ctrl + A). The blur is now restricted to your glass shape.

Step 4: Add the Glass Tint and Opacity

  1. Create a new transparent layer by clicking the New Layer icon at the bottom of the Layers panel. Name it Glass Tint.
  2. Place the Glass Tint layer directly above the Blurred Background layer.
  3. Pick a light color (pure white #FFFFFF works best for standard frosted glass) and use the Bucket Fill Tool (Shift + B) to fill the canvas or selection.
  4. If you filled the entire canvas, copy the layer mask from the Blurred Background layer:
    • Right-click the Blurred Background mask, choose Mask to Selection.
    • Select the Glass Tint layer, right-click, choose Add Layer Mask, and select Selection.
  5. Lower the Opacity of the Glass Tint layer to around 10% - 25% to allow the blurred background underneath to show through clearly.

Step 5: Add Border Highlights and Depth

  1. Create another new layer above Glass Tint and name it Glass Border.
  2. Right-click the mask on your Blurred Background layer and choose Mask to Selection.
  3. With the selection active, go to Edit > Stroke Selection...
  4. Set the line width to 1px or 2px, ensure the color is white, and click Stroke.
  5. Deselect via Select > None.
  6. Lower the opacity of the Glass Border layer to around 30% - 50% for a subtle, translucent edge.

Step 6: Add a Drop Shadow (Optional)

  1. Select the Blurred Background layer.
  2. Go to Filters > Light and Shadow > Drop Shadow...
  3. Adjust the Opacity, Blur Radius, and offset values (X and Y) to give the glass element a floating appearance.
  4. Click OK to finish.