PNX1301EH NXP Semiconductors, PNX1301EH Datasheet - Page 220

• Manufacturer Part Number: PNX1301EH
• Manufacturer: NXP Semiconductors

Specifications of PNX1301EH

• Lead Free Status / RoHS Status: Not Compliant

PNX1300/01/02/11 Data Book
against a bright blue background while inhibiting the blue
background.
14.5.6
Short output codes, such as RGB 8, have few bits for out-
put-value determination. RGB 8R has (2,3,3) bits for
(R,G,B). The result is a coarse, patchy image if nothing
is done to correct for the limited resolution. Dithering sig-
nificantly improves the effective resolution of these imag-
es. For example, RGB 8 images dithering looks nearly as
good as RGB 16.
Dithering works by adding a random dithering value to
the pixel before it is truncated by the output formatter.
The dither is added to the portion which will be truncated.
The carry from this add will occasionally propagate into
the most significant portion of the pixel before truncation.
The carry from the add thus ‘dithers’ the displayed val-
ue.In the example shown in
er value is added to the original data before truncation.
The dither value should have a range of from approxi-
mately 0 to 1 LSB of the truncated value. The dither value
should be symmetrical around 1/2 the LSB of the quan-
tizing error of the truncation. In the example shown, the
dither signal has values of (1/8, 3/8, 5/8, 7/8). This set of
values has a range of approximately 0 to 1 LSB, and it is
symmetrical around 1/2 LSB.
In this example, the input signal has a value of 2.83.
Without dithering, this value would be truncated to an
output value of 2 in all cases. Averaging the un-dithered
signal over four pixels still gives you a value of 2. By add-
ing the dither signal, the output value is 2 or 3 depending
on the value of the added dither signal. Averaging over
four pixels, the average output value is 2.75, much closer
to the input value than without the dither signal. The dith-
er signal has significantly reduced the error when aver-
aged over four pixels.
Two types of dithering are combined in the ICP: quad pix-
el and full image dithering. Quad pixel dithering, also
known as ordered dithering, adds one of four dithering
values to each pixel. The four dithering values corre-
14-10
Figure 14-10. Dithering
No Dithering
3
2
1
0
Dither = 0
Output = 2
No Dithering:
Output = 2.0
Error = +0.830
2.830
Dithering
PRELIMINARY SPECIFICATION
Figure
14-10, a random dith-
3
2
1
0
Dither = 1/8
Output = 2
2.955
3
2
1
0
1/4 LSB Dithering
Output = (2+3+3+3)/4 = 11/4 = 2.750
Error =(2.830 - 2.750) = +0.080
Dither = 3/8
Output = 3
spond to four-pixel quads in the output image. The pixels
in each quad have fixed positions in the input image, so
the dither values are chosen on the bases of odd or even
line number and odd or even pixel number in the line.
The dither values of (0/4, 3/4, 2/4, 1/4) are added by line
and pixel number: even line & even pixel, even line & odd
pixel, odd line & even pixel, odd line & odd pixel. This
gives a four value ordered function for four adjacent pix-
els in the image. The (0,3,2,1) pattern is chosen specifi-
cally to prevent pairs of high or low pixel values from
clustering. Spatial dithering provides a significant im-
provement in effective resolution.
Full image dithering adds a single randomly generated
number to every pixel of the image. The result is that the
intensity and color accuracy increases as the size of the
sample is enlarged. The random number has a long bit
length to prevent repeating patterns in the image. The
random number can be static or dynamic. In the static
case, the random number generator starts with a fixed
seed at the start of the image. The random number spa-
tial pattern is fixed for the image even though the image
data may change from frame to frame. In the dynamic
case, the random number generator runs continuously,
and the dithering pattern changes from frame to frame.
The ICP combines quad pixel dithering with full image
dithering to provide the final dithering signal for each pix-
el. The quad pixel dither provides the two most signifi-
cant bits of the dither signal, and the full image dither pro-
vides the least significant 4-bits of the dither signal. The
combined dither signal is 6 bits.
From 1 to 6 bits of dither signal are used, depending on
the output format. If fewer than 6 bits are needed, only
the MSBs of the dither signal are used. For example in
the RGB 8R output format, the R output value is 3 bits in
size. The output uses the 3 MSBs of the R input value
and truncates the 5 LSBs. The dither unit adds 5 bits of
dither signal (the 5 MSBs) to the 5 LSBs of the R input
value before truncation, and the RGB formatter truncates
the result after adding.
3.205
1/4 LSB Dithering
3
2
1
0
Dither = 5/8
Output = 3
3.455
Philips Semiconductors
3
2
1
0
Dither = 7/8
Output = 3
3.705