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  Understanding Transparency Masks In Canvas™ 6 - Part One

Deneba Canvas 6 offers many combinations of transparency effects with the use of masks. Canvas 6 also provides for general object opacity in addition to the use of transparency masks. A mask is different in that it is an overlay for your art that allows some areas to show through while blocking out others. In the case of a transparency mask, it is an object which uses grayscale data (whether  grayscale data from a bitmap or vector representation of grayscale) in which the white areas allow the image to show through and the black areas act to block the image thus rendering these areas transparent.

There are two types if transparency masks in Canvas - vector and bitmap. Where one of these types uses vectors to define the mask areas, the other uses pixels. In Canvas, a pixel-based or bitmap mask is called a Channel Mask because it is stored as a grayscale channel similar to an alpha channel used to store a selection marquee an in image.

Either type of transparency mask can be attached to any type of object. This makes Canvas very flexible in that it allows either a channel mask or a vector mask to be attached to either a paint object, vector object or text object. The chart below illustrates the concept:


As a result, there can be a lot of varied combinations of objects and transparency masks. In this tutorial we will explore some of them.

Vector Transparency Masks

The concept of using a vector object as a mask is very simple, really. Bitmap transparency masks have been around for years in image editors such as Adobe® Photoshop®. Vector gradients have also been around for years in illustration programs including Deneba Canvas, CorelDRAW®, Adobe Illustrator® and Macromedia® FreeHand®. Canvas 6 applied the concept of using a vector gradient as a mask.

The gradient in a vector transparency mask has one of four basic shapes. These are the same as the basic gradient shapes available in the Inks palette for strokes and fills - radial, directional, rectangular and elliptical. In the Toolbox are a set of tools for creating vector transparency masks:

The Vector Transparency tools lie under the effects tools in the toolbox

  Tear off the Vector Transparency tools
and select a tool
cnvmask02.gif spacer.gif cnvmask03.gif

Masks made from each of
these tools can be created
using the Transparency
palette (below)
cnvmask04m.gif   Alternately, the Transparency palette can be used to create each of the four basic vector transparency masks as well as a channel mask.

Transparency Mask Examples

1. To create a transparency mask simply select the object you wish to mask and either click Object > Transparency > New Channel Mask to make a channel mask or use one of the Vector Transparency tools described above to create a vector mask. Alternately, you can use the Transparency palette. Shown below are two images - a bitmap (paint object) on the left and a vector image on the right. We will attach a vector mask on one and a channel mask on the other, then we'll switch them around.

cnvmask05.gif cnvmask06.gif
cnvmask07.jpg   2. Let's start with the paint object. Select it, then choose the Elliptical Transparency Tool and drag an elliptical mask over the image. Adjust the handles until you achieve the desired effect.
cnvmask08.jpg   3. The result is a pleasant vignette which focuses on the building.

4. For the vector object, let's create a channel mask. Select the image and click Object > Transparency > New Channel Mask. In the dialog, choose 72 ppi for the resolution, then click "OK" (below right). Canvas throws a paint object over the image and puts into edit mode. Begin by choosing the Oval Marquee tool and drag out an oval-shaped selection (below left).

Tip: Use Ctrl-Drag from the center outwards (Mac® users begin dragging before pressing Control). For instructions on how to float and move the selection to reposition it,
click here.

cnvmask09.gif cnvmask13.gif

5. Next click Image > Select > Inverse, then Image > Select > Feather. In the dialog, enter a feather radius of 25 pixels. Click "OK" when done.

cnvmask10.gif cnvmask14m.gif

Click Here To Continue...


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