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| MASKING
BY PATTERNS
On This Page: • Examples
of Pattern Masking • Research on Masking • Reducing
Masking
Surrounding patterns can reduce the legibility of symbols and text. There
are several different perceptual phenomena that involve interference
among adjacent pattern elements. Some have been referred to collectively
as pattern "masking." For designers of graphics the message
is that one must be very cautious in use of patterned background
fields and wary of closely spaced symbols.
Examples
of Pattern Masking  |
![2 different linear background patterns interfere with the readability of text.]()
![A variety of dotted background patterns behind text. The resulting text is unreadable.]()
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Patterned
backgrounds . Background patterns (hatching, textures) with
high luminance contrast can interfere with the legibility of
symbols. All
of these backgrounds reduce legibility relative to the isolated
text (center panel, top figure). |
![Demonstration of the poor readability of overlapping text and text with poor spacing between letters.]()
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Text Problems
. Problems internal to text and symbols can reduce legibility.
In the top panel of this figure two overlapping text labels interfere
with each other, making both less legible than the unencumbered text
in the middle panel. The text in the bottom panel is too tightly
packed
horizontally. Less extreme reduced spacing can also hinder
legibility. |
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| Research
on Masking
Most recent research
on interference among patterns has been based on analyses of the patterns
in the spatial and temporal frequency domains. As in other research
on spatial vision the stimulus patterns have often been periodic patterns
or
visual
noise.
The phenomena
studied have
mostly involved detection of a low-contrast target signal (a particular
component of the pattern) in the presence of a higher contrast masking
pattern.
In very simple terms, the general
conclusion has been that thresholds for detecting the signal are elevated
by masking patterns that have spatial frequencies and
orientation and temporal characteristics similar to the
signal. While some of the interference likely due to interaction
of local features of the signal and masking
pattern, at least part of
the masking is thought to involve more global processes.
In design of graphic
displays we are less concerned with detection of the presence of a
pattern and more concerned with discrimination of suprathreshold symbols.
This task involves legibility of differences of local features
of the
symbols. For these purposes the most direct level of explanation is
in terms of
interaction of the local features of the masking and symbol patterns.
Some of these local effects can be easily seen in magnified images
of the above examples: |
| ![Close up looks at text with dotted and linear backgrounds. The close up shows how the background combines with the text elements to create new patterns.]()
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The dot elements of the background textures combine with the strokes
of the text to form new elemental patterns. In the worst cases
(upper left,
lower right) the elements of the texture pattern are about the same size
as strokes in the individual letters. Even the sparser patterns
interfere.
In the "Text
Problems" figure above, the same local shape distortion is at
work in the top panel. In the bottom panel a second problem, known
in reading
research as "crowding," also occurs. Letters that are close
but not touching are harder to read than properly spaced text. |
| |
![A closeup of of lower luminance dotted and linear backgrounds against black text. the lower luminance elelments do not create or interfere with the textual patterns.]()
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In this revised figure increasing the luminance difference between
the texture pixels and symbol pixels restores the contours that
define
the
symbols'
distinctive
features.
Even at this reduced contrast the lower right pattern interferes
somewhat
with legibility of the symbols. |
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![Higher luminance linear background overcome by removal of the background around the text.]()
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The local effects
of the background texture can be reduced or eliminated by removing
the texture
locally.
More on background infills Last
Resorts: Outlining / Infills. |
![Removal of the high luminance contrast dotted background around text can allow for better readability.]()
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Related Topics:
Designing
with Luminance Contrast
Last
Resorts: Outlining / Infills
Labeling
with Color
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