On This Page: Examples
of Pattern Masking Research on Masking Reducing
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.
of Pattern Masking
backgrounds . Background patterns (hatching, textures) with
high luminance contrast can interfere with the legibility of
of these backgrounds reduce legibility relative to the isolated
text (center panel, top figure).
. 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
horizontally. Less extreme reduced spacing can also hinder
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
mostly involved detection of a low-contrast target signal (a particular
component of the pattern) in the presence of a higher contrast masking
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
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:
The dot elements of the background textures combine with the strokes
of the text to form new elemental patterns. In the worst cases
lower right) the elements of the texture pattern are about the same size
as strokes in the individual letters. Even the sparser patterns
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
research as "crowding," also occurs. Letters that are close
but not touching are harder to read than properly spaced text.
In this revised figure increasing the luminance difference between
the texture pixels and symbol pixels restores the contours that
Even at this reduced contrast the lower right pattern interferes
with legibility of the symbols.
||The local effects
of the background texture can be reduced or eliminated by removing
More on background infills Last
Resorts: Outlining / Infills.
with Luminance Contrast
Resorts: Outlining / Infills
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