Mask for Transparency

Menu -> Layers -> Mask for Transparency

Masks for transparency enable you to hide and reveal parts of a layer and to apply special effects with precision. Masks can be created from selections, from images, from the luminance values of images, and from scratch. They can cover a layer completely or with varying levels of opacity. Because they are in grayscale, masks are saved into alpha channels of the layer.
Image Unmasked
Shows the image not masked.
Transparency Mask
Shows the mask for transparency. It is a grayscale image.
Color
The "Color" radio button allows you to define the transparency according to the selected color.
Hue
The "Hue" radio button allows you to define the transparency according to the selected color converted to hue. Luminosity and saturation of color are ignored.
Pipette
Use the Pipette to pick up a colour from one part of the image and select the transparent color. Press this button and click on the unmasked image to determine the transparent part.
Range
You can set the range of tolerance for similar colors which wish to selected.
More Options Menu

Load the transparency mask from an image file. The image is converted to grayscale.

Save the transparency mask in a BMP image format. The image is saved in grayscale.

Clear the transparency mask. The mask is filled in with white.

Invert the transparency mask. Make an image in negative. Inverting a mask reverses its transparency: what is black becomes white, and what is white becomes black. Grays are assigned their mirror transparency. To invert a mask, choose Invert from the Options menu.

Smooth Edge and Smooth Edge More function are used to soften the edge of a transparency mask. This function is based on a threshold algorithm.

Copy the transparency mask to the clipboard.

Paste the transparency mask from the clipboard. The image is converted to grayscale.

Merge the transparency mask from the clipboard. The image is converted to grayscale and is merged with the current transparency mask.

Zoom In, Zoom Out and Scale 1:1
Click Zoom In button to increase the zoom factor.
Click Zoom Out button to decrease the zoom factor.
Click "Scale 1:1" button to set the scale to 100 %.