What is Masking?
As more and more printers try their hand at photorealistic images on shirts,
the problem always starts with the question of how do you remove the background
from the image. If you want to put a large tiger head on a shirt, you must
first acquire a photo of the tiger and then figure out how to remove the
bushes and shrubs from behind him (figure 1). The non-printing area around
an image is called the canvas.If the image is going on light and dark shirts you may need one version
of the art with a white canvas (figure 2) and one version with a black
canvas (figure 3). The removal of a background is often called masking.
Also, if you plan to build the design using various layers in Adobe Photoshop,
the image will need the background turned transparent.
There are a number of third party programs that do this such as Extensis
Mask Pro. These programs cost sell for less than $100 to over $500. This
article will show you how to do masking directly in Photoshop 5.5 without
any additional programs.
Images With Solid Backgrounds
You always pray that the image has a solid color background and a hard
edge because designs like these are easy to mask. You can simply use the
Magic Wand Tool to select and delete any unwanted backgrounds. If the
image has a yellow background, why not just leave it? Since the canvas
is the non-printing area, you don’t want this to be a color because whether
you separate by selecting color or use automated programs, the background
color has nothing to with the image separations. It looks pretty to see
the image on the shirt color BUT this color has nothing to do with the
printable colors. It must be removed before separating.
To remove solid backgrounds, first, double-click on the Magic Wand tool.
This will bring up the Magic Wand Options menu. The default setting for
the number of similar pixels it will select is 32. This will work for
most designs. If the image has a hard edge make sure to uncheck Anti-Aliasing.
Anti-Aliasing will tend to soften the edges and this may give you a slight
ringing or ragged edge to the image.
Next, place the cursor in the canvas area around the image and click.
The Magic Wand tool will select all of the areas around the image of the
same color. It will make this area a Selection and place the “marching
ants” around this selection (figure 4).
Make sure the Background Color on the Toolbar is set for either black
or white (depending on the color you want as the mask or canvas. Now,
just press the Delete Key and whatever is selected will be replaced with
the Background color (figure 5). It’s that easy!
If the image is low resolution or has some soft edges, the Magic Wand
Tolerance of 32 may be too low. If you get a little “ringing”
or edge artifacts, increase the Tolerance setting (figure 6).
You can do the same thing with the Magic Eraser in Photoshop 5.5. The
only difference is that it will erase the background to transparency which
is helpful if you are going to build a design using layers.
To use the Magic Eraser, double-click on the tool to bring up the Magic
Eraser Options Menu. The default setting is 30. Click on the area around
the image and watch the entire area around the image turn to checkerboards
(transparent). See Figure 7.
Images With Soft Vignetted Edges
Images that have soft edges that blend to nothing are a little harder.
You may have to actually use the Airbrush Tool and paint around these
images with white or black. This takes practice and will require some
experimentation with the size of the brush tip. Simply open the Brushes
Palette (Window/Show Brushes), select a brush tip, change the Foreground
color on the Toolbar to black or white, select the Airbrush tool, and
start painting (figure 8).
Masking Functions in Photoshop
In version 5.5 of Adobe Photoshop, a rudimentary masking program called
Extract was added. I call it rudimentary because it is OK and not great.
They also added a very similar tool called the Background Eraser. Both
of these tools erase the background to transparent.
The advantage to these two tools is they work where there are irregular
edges such as trees or grass behind an object. They also work where you
have hair, fur or other softer edges.
To use Extract, open the image and then open the Extract menu (Image/Extract).
Extract works by having you draw around the area you want to extract with
a tool called the Edge Highlighter. Select the Highlighter tool by clicking
on the top tool in the Extract Toolbar. You can adjust the “size”
of the Highlighter tip in the Tool Options/Brush Size window. The actual
cursor tip will show you how big the tip is.
It is hard to describe, but if you put the cursor over any edge area
of the image where you want to remove the image from the background and
click and drag, you will start to highlight with a green line. Make sure
to highlight over the edge of the image and the background (figure 9).
Again, keep the tip as small as possible and try to highlight over the
edges as accurately as you can. If you draw too much or are not happy
with your work you can use the eraser tool on the toolbar and do touchup.
When you are done highlighting all the way around the image (you must
go all the way around and close the shape) you need to “fill”
the highlighted area. Again, this may seem hard, but simply select Fill
Bucket from the Extract menu toolbar and click in the center of your image.
The color blue fills the shape (figure10). Yes, it looks weird!
To make the extraction more accurate, change the Smooth slider in the
Extraction portion of the menu to 30 (0 is the least accurate setting).
The next step is easy. Simply click on Preview. It can take a few minutes,
but when done, the background is transparent and the image is extracted
(figure 11). If you don’t like what you have done, you can look at the
original again by selecting Original from the Preview menu section. You
can even load your painting (highlight) and fill again so you can do more
When finished, press OK and the image has been extracted from the old
background and now has a new transparent background. If you want the image
on a white or black background – after performing the extraction – make
a new layer in the Layers Palette. Place this layer below the extracted
image and fill it with the color of choice (figure 12). Next, simply flatten
the layers and you have the image on a solid background.
This tool is similar to extract except it doesn’t work well with soft,
detailed edges. It is my least favorite method. To use the tool, double-click
on it to open the Options menu. A tolerance setting of 32 with Anti-Aliasing
turned off, and the Opacity set to 100% is a good start.
Next, bring the tool over the image and close to the edge. Move the tool
around the edge as you would normally do with the eraser. Photoshop finds
edges of differing colors and erases the outside color to transparency
Removing images from background is a critical part of building and separating
images in Adobe Photoshop. If you use the Layers Palette to build designs
you will need transparent backgrounds for the various components. When
color separating specific images you will need to extract them from their
backgrounds and fill the canvas around them with white or black. This
can all be done using the techniques outlined in this article.