The next three filters—Maximum, Minimum, and Median—are
in the Noise category.
They are the principal tools for a category of techniques that involved
extensive operations with the individual channels in Photoshop.
They were known as channel ops (CHOPs).
Before Photoshop got sophisticated, most of the effects we take for granted
were created using CHOPs.
Now the need for CHOPs has diminished, but the Maximum, Median, and Minimum
filters still have important roles to play in the area of mask manipulation.
Maximum Filter
The Maximum filter makes the lighter pixels larger
and shrinks the darker ones.
With the Percentage slider (1-100), you can control the amount of filtering
applied to the affected pixels.
The greater the value, the darker the affected pixels become.
The Radius slider (1-20 pixels) determines the number of pixels that are
successively selected and affected. |
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In the next image, the Radius was set to 5 pixels and the Percentage set
to 60.
The result visually demonstrates the filter action.
The white area expands by 5 pixels in all directions, while the black area
shrinks. |
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However, the percentage setting dictates that the 5-pixel expansion be
only 60 percent affected, so the expanded area is 60 percent gray.
Now, what is the difference between applying the Maximum filter to a mask
and using Mask/Shape/Expand?
Other than the ability to control the percentage, the results are identical. |
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The Minimum Filter
Quite simply, the Minimum filter is the evil twin of the Maximum filter.
It makes the lighter pixels smaller and the darker ones larger.
When applied to a mask in Paint on Mask mode, the white portion of the mask
shrinks. |
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Applying the Minimum filter to a mask is equivalent to choosing Mask/Shape/Reduce,
except for the ability to modify the percentage of effect.
Notice that with both filters, the expansion or reduction of the mask does
not follow the shape of the original very well.
That is because the greater the increase, the greater the amount of distortion
that is introduced into the resulting shape.
The best way to expand or contract the mask of a single object or single
character of text is to use the Mask Transform tool and drag the corner
handles.
This technique will not work on a string of text because the kerning (spacing
between the characters) goes out the window. |
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What can you do with an expanded or reduced mask?
Here is a suggestion for something you can experiment with.
Type some text (use a thick sans-serif text, because on thin text the effect
is lost).
Create a mask from the text. Next select Paint on Mask mode and apply the
Minimum filter with the percentage you want.
You now have a nice border surrounding your text. Out of Paint on Mask mode,
select Edit/Fill and choose a different fill.
Invert the mask and apply The Boss filter to the edge.
The result is shown in the following image: |
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The Median Filter
This filter simplifies the colors or shades in an image by reading the brightness
of adjacent pixels of noise and averaging out the differences.
Its ability to remove noise is dependent on the type of noise (sharp and
high-contrast or blurred and low-contrast) in the image.
One use is to smooth the rough areas in scanned images that have a grainy
appearance.
It does remove noise, but at the expense of making the image much softer
(which sounds better than "blurry"). In Figure below, the original
image (left) has the Median filter applied.
As you can see, the noise, along with about everything else, has been removed. |
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Figure:The original (on the left) and the image after the application
of the Median filter.
This filter uses a Radius slider to set the percentage of noise removal
that is applied.
The filter looks for pixels that are isolated and, based on the Radius setting
in the dialog box, removes them.
The Median filter tends to blur the image if it is set too high.
It has been my experience that if you are working on an image smaller than
a billboard, you don't want to use a setting higher than 2.
The Real Power of Median
The secret is to use it with the Paint on Mask mode.
Here is a quick session that will prove my point. |
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1. Create a new image.
Make sure the Paint is set to black, select the Text tool, and change the
font to GoudyOlStBT. Type "Antico".
Select the Object Picker tool, and center the text on the image (CTRL-A).
2. Create a mask (CTRL-M) and select Paint on Mask (CTRL-K).
Choose Effects/Distort/Displace. Select Rusty.PCX as the displacement map.
Change the Horizontal and Vertical settings to 20. Click OK.
3. Choose Effects/Noise/Median.
Change the Radius setting to 4 and click OK.
The amount of Radius used depends on the size of the object.
4. Exit Paint on Mask (CTRL-K) and choose Object/Crop to Mask. |
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That's all there is to it.
I also use this filter to create corroded and perforated metal effects.
Here are some additional ideas.
You can add a background that looks a little like parchment or old paper. |
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