Like an alpha channel in a paint object, a channel mask is basically a grayscale image. Channel masks can be edited using image-editing tools and techniques, similar to alpha channels.
You can think of a channel mask as a template for transparency. The channel mask is the same size as the masked object and is aligned with it. In the case of a paint object, the channel mask has the same resolution and number of pixels as the paint object.
In an alpha channel, luminance corresponds to selection intensity. In a channel mask, luminance values correspond to 256 levels of transparency, from 100% to 0% transparency, in the masked object. Black pixels (0 luminance) produce 100% transparency, while white pixels (255 luminance) produce 0% transparency.
Therefore, when you paint in a channel mask, painting with black produces clear areas and painting with white produces opaque areas in the masked object. Painting with gray produces partial transparency relative to the gray value, with darker grays producing greater transparency than lighter grays.
Black in a channel mask produces 100% transparency. A feathered edge produces partial transparency.
Channel mask and paint object
Keep in mind that an object’s appearance can be affected by its transfer mode, scope setting, and opacity, in addition to a channel mask. Changing the transfer mode can completely change the appearance of an object that has a channel mask. (See Using Transfer Modes.)
You can create a blank channel mask, or create a channel mask from a paint object. You create a channel mask when you render objects. (See Rendering Objects and Images.)
You can use the Transparency palette, Sprite tool, or the Channels palette to create blank channel masks. (See Channel Masks for more information about the Channels palette.) In the Transparency palette, the Mask menu shows “Channel” when a selected object has a channel mask.
This procedure creates a blank channel mask for an object.
When you create a new channel mask, the channel is filled with white pixels. At this point, the channel mask produces no transparency because white pixels in the channel mask produce 0% transparency in the masked object. As you edit the channel, painting with gray produces partial transparency, and painting with black produces 100% transparency.
Select the Sprite tool and click on the selected object.
The object switches to Image Edit mode.
You can identify whether you are in Image Edit mode by the Status bar or the following icon in the Properties bar:
When you apply a channel mask to a vector object, the channel mask affects the vector object’s fill ink or fill ink and stroke (pen ink). To change the effect, change the Scope option in the Properties bar or Transparency palette. (See Controlling the Scope of Transparency Effects.)
You can create a channel mask by attaching a paint object to another object. If you have an existing paint object that you want to use as a channel mask, it’s quicker to use this procedure than to use the Channels palette to place the paint object in a channel mask.
If the paint object and the object to be masked aren’t the same size, Canvas X Draw scales the image of the paint object to fit the masked object.
A channel mask created from a paint object is the same as any channel mask. You can edit it the same as if you created a blank channel mask.
Like any other channel mask, a channel mask created from a paint object produces transparency relative to its gray values. If the channel mask is solid white, it creates no transparency; if it is solid black, it creates 100% transparency and makes the masked object invisible.
You can use painting tools, filters, and image-editing commands to modify the effect of a channel mask.
Place the masked object in channel mask edit mode.
Editing a channel mask is similar to editing a channel in a paint object. You can paint in the channel mask with shades of gray. You can make selections with selection tools, commands, and alpha channels. You can apply image-adjustment commands and filters to the entire channel mask or to just the selected areas.
You can enter Channel Mask Edit mode using any of the following methods.
If the object doesn’t have a channel mask, this creates a channel mask and puts the object in Channel Mask Edit mode.
In this mode, the channel mask is active and the object is also visible. You can paint in the channel or modify it to change the transparency of the underlying object.
You have a choice of view when you edit an object’s channel mask. You can display the object and the channel mask together, which shows you the overall effect of the mask as you edit it. Or, you can hide the object to concentrate on the channel mask alone.
For information on selecting views with the Channels palette, see Editing Channel Masks.
You can use the Transparency palette to change your view when you edit a channel mask. In Channel Mask Edit mode, two buttons let you select editing views. Click the triangle at the lower left to expand the palette if necessary to display the buttons.
In the Transparency palette, click Channel Mask Only. This is the same as hiding the “object channel” in the Channels palette.
Click Image and Channel Mask. This is the same as making the “object channel” and the channel mask visible in the Channels palette.
Removing a channel mask from an object removes the transparency effect produced by the channel mask.
When you detach a channel mask, Canvas X Draw converts the channel mask to a paint object and places it in the document. The paint object includes the alpha channels from the masked object if it had alpha channels.