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SmoothPicture™ Technology
While the diamond grid DMD effectively improves system cost, by itself it is
insufficient to display all of the original image
pixels on the screen. The original image
would have to be filtered to produce an
image with half the number of pixels of the
original image in order to be displayed on the
DMD. TI's SmoothPicture™ technology
combines the diamond grid DMD, with its
inherently high mirror switching speed and
an optical actuator to create a system which
can display a full resolution image
onscreen containing all of the original image
pixels. With SmoothPicture™, the actuator
optically displaces the DMD image horizontally,
coordinated with the display of two
separate subframes of data on the DMD (see
Figure 3). Utilizing the high switching speed
of the DMD, both subframes of data
containing all of the original pixels in the
image can be displayed within one 16ms
field time.
Referring to Figure 4, each incoming video
frame is parsed into the two separate
subframes, one subframe containing all of the
odd image pixels, the other containing all of
the even pixels. The 16ms video field time is
subdivided into two 8ms subfield times.
During the first subfield time, the odd
subframe data is displayed. At the beginning
of the second subfield time, the actuator horizontally
shifts the DMD image by ½ pixel, and
the even subframe data is displayed. The
resulting onscreen image contains all of the
pixels in the original image frame, and is
constructed within one 60Hz video field time.
Note that even though a diamond grid DMD is
used, the horizontal displacement
methodology recreates the original orthogonal
grid of the HD image frame. An additional
benefit of the ½ pixel displacement is that it
effectively softens the pixel edges. In static
orthogonal displays (using a 1 mirror to 1 pixel
display ratio) the mirror edges are distinctly
visible which in some display technologies
results in the familiar screen door effect. With
SmoothPicture™, this artifact is mitigated
resulting in a seamless, more film-like image.
Effective SmoothPicture™ Display Resolution
The effective resolution of a display device
can be quantified by measuring the display
system Modulation Transfer Function, or
MTF.
The MTF of a display system is a measure of
the display's spatial frequency response. It
quantifies the display contrast at a given
spatial frequency relative to the display
contrast at DC (i.e. a flat field). MTF is
typically measured in the form of line pairs per
unit distance, a line pair consisting of a bright
line coupled with a dark line. High spatial
frequencies correspond to fine image detail.
The more fine image detail that can be
displayed, the sharper the image.
During the development of SmoothPicture™
Technology, Texas Instruments evaluated the
MTF performance of the SmoothPicture™
based display systems with respect to other
display technologies used in 1080p rear
projection television displays. Figure 5 shows
the MTF of a SmoothPicture™ based 1080p
DLP display relative to the MTF of two
leading, commercially available LCOS based
1080p rear projection TVs. Note that the DLP
display curve rolls off at a higher spatial
frequency, indicating that it more effectively
translates the 1920 x 1080 addressed image
resolution into effective resolution at the
eyeball.
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