Channel Masks

Channel masks apply transparency effects to objects, including paint objects, vector objects, text objects, and group objects. A channel mask creates transparency in proportion to the luminance of its image.

A channel mask is a grayscale image channel. Black pixels in a channel mask produce 100% transparency in corresponding areas of the masked object. White pixels in a channel mask produce 0% transparency in the masked object. Gray pixels in a channel mask produce partial transparency in the masked object. Darker grays produce greater transparency than lighter grays.

Channel masks are powerful because they let you use painting and image-editing techniques to create transparency effects, and because a channel mask can be applied to any type of object. An object’s channel mask is the same size as its bounding box. You can detach or delete an object’s channel mask to eliminate the transparency effect.

Creating Channel Masks

Use the mouse, New Channel Mask command, Sprite tool, Transparency palette, or Channels palette to make channel masks.

To Create a Channel Mask:

Do one of the following:

• Ctrl+double-click the object to be masked.
• Select the object to be masked and choose Object | SpriteLayers | New Channel Mask.
• Click on the object with the Sprite tool.
• Select the object to be masked. In the Transparency palette, choose Channel in the Mask menu.
• Canvas X Draw creates the channel mask and puts the new mask in Edit mode.
• If the object is a paint object, Canvas X Draw creates a channel mask with the same resolution as the paint object.
• If the object is a vector, text, or group object, the New Mask dialog box opens. Type the resolution you want for the channel mask and click OK. Canvas X Draw creates the channel mask with the specified resolution.

To Use the Channels Palette:

You can create a channel mask for a paint object from an existing alpha channel or color channel.

With a paint object in Edit mode, drag an alpha channel into the channel mask slot in the Channels palette. If the slot already contains a channel mask, the channel you drag there replaces the existing channel mask.

Editing Channel Masks

You can edit an object’s channel mask to change the transparency effects it produces. Generally, you can do anything that you can when editing a color channel, alpha channel, or grayscale image: use painting tools, filters, and image-adjustment commands, make selections, and paste selections into a channel mask.

To Edit a Channel Mask:

Do any of the following to place a channel mask in Edit mode:

• Ctrl+double-click the masked object.
• Select the masked object and choose Object | SpriteLayers | Edit Channel Mask.
• Select the masked object and click Edit in the Transparency palette.

An eye symbol in the Channels palette appears to the left of a channel that is visible. The eye symbol disappears if a channel is hidden.

When you edit a channel mask, the top channel in the palette represents the object itself. For a typical paint object this channel is labeled with the image mode, such as RGB or CMYK. For other objects, the first channel is labeled “Object”. (See Transparency Masks.)

The channel mask of an object in Edit mode is shown in the Channel Mask slot, which is below the channel list.

To View the Channel Mask Only:

Click the eye symbol next to the object or composite channel at the top of the channel list. This hides the object channel so only the channel mask is visible.

To Hide the Channel Mask:

Click the eye symbol next to the channel mask. This hides the effect of the channel mask on the object.

At least one channel, either the composite/object channel or the channel mask, must be visible. If only one is visible, you can’t hide it by clicking its eye symbol.

To Display a Hidden Channel:

Click to the left of the channel to restore the eye symbol.

When you edit paint objects you can edit pixels in the images by selecting channels in the Channels palette. However, when you edit other objects, you can’t select the “object” channel. You can show or hide the object channel, but you can edit pixels only in the channel mask.

When you finish editing a channel mask, press Esc to leave Edit mode.

Detaching and Deleting Channel Masks

If an object has a channel mask, the channel mask controls the transparency of the object. You might want to detach or delete the channel mask to eliminate the transparency effects from the object.

When you delete a channel mask, it no longer exists in the document. When you detach a channel mask, it appears in the document as a separate grayscale paint object.

To Detach a Channel Mask:

Select the masked object. Choose Object | SpriteLayers | Detach Mask.

When you detach a channel mask, Canvas X Draw removes the channel mask from the object and places it in the document as a separate grayscale paint object. If the channel mask was detached from a vector object, the resulting paint object will contain any alpha channels that were contained in the vector object.

To Delete a Channel Mask:

1. Select the masked object.
2. In the Transparency palette, choose None in the Mask pop-up menu.

Deleting the channel mask of a vector, text, or group object also deletes any alpha channels that were contained in the object. Also, if you ungroup a group object that has a channel mask, Canvas X Draw deletes the channel mask.

You can delete a paint object’s channel mask when the paint object is in Edit mode by dragging the channel mask to the Trash can icon at the bottom of the Channels palette.

See also:

• Transparency Masks