Channel masks let you add transparency to images without altering them permanently. A channel mask creates transparency without changing any pixels in an image. You can remove a channel mask to eliminate the transparency effect at any time.
To make parts of an image transparent—to eliminate the background in a photograph, for example—you can create a channel mask from a selection. This procedure explains how to transfer a selection into a channel mask to make selected areas transparent.
Create a transparent fade effect using a channel mask. This procedure explains how to create a blend in an alpha channel, and then create a channel mask to make an image fade to transparency.
Canvas X Draw can create a channel mask when you render a vector, group, paint, or text object.
To create the mask, choose the Mask and Transparency options in the Render dialog box. Canvas X Draw will create a channel mask that makes blank areas around and inside the objects transparent.
When you make a new paint object by pasting a non-rectangular selection copied from an image, Canvas X Draw makes a channel mask to hide white pixels surrounding the selection.
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Select the Preserve Visibility checkbox in the Channels palette to preserve transparency when you paint or apply filters to an image. The Preserve Visibility checkbox is available when you edit a paint object that has a visibility mask. A paint object has a visibility mask if it was created with a transparent background, or if you applied a visibility mask with the Add Visibility Mask command.
If a paint object has an opaque background, the Preserve Visibility checkbox is disabled.
When a paint object is in Edit mode, select Preserve Visibility in the Channels palette. When selected, you can paint and edit the image without affecting clear areas or reducing the transparency of partially transparent pixels.
The Preserve Visibility option affects all aspects of image editing. When Preserve Visibility is selected, pasted selections do not affect clear areas. Also, a pasted selection will match the transparency of the existing pixels when you defloat the selection.
If an image is completely clear (contains no colored pixels), you cannot alter the image when Preserve Visibility is selected.
You must deselect Preserve Visibility to paint in clear areas of an image. Then, if you want to edit the painted areas, select Preserve Visibility again.
For example, you can deselect Preserve Visibility and paint airbrush strokes in a clear image. Then, select Preserve Visibility and you can paint over the airbrush strokes to change their color, without losing the soft edge or “spilling” color into clear areas.
When Preserve Visibility is selected and you use the Eraser tool, pixels you “erase” are painted with the current background color; they are not erased to clear. Also, when you use any painting tool to apply color, you cannot make pixels more or less transparent. This is why you cannot apply any color in clear areas when Preserve Visibility is selected.
When you select Preserve Visibility, you can paint and apply filters to modify pixels that are less than 100% transparent. You can change the hue, saturation, and intensity of pixels but can’t change their transparency.
Deselect Preserve Visibility. This turns off the visibility mask and lets painting tools and filters affect the entire image.