ASX340AT Datasheet, PDF (20/75 Pages) ON Semiconductor – Color CMOS NTSC/PAL Digital Image

ASX340CS: 1/4-Inch Color CMOS NTSC/PAL Digital Image Sensor
Sensor Pixel Array
Table 9:
NTSC (continued)
Line Numbers
20-263
264-265
266-282
283-525
Field
1
1
2
2
Description
Active video
Blanking
Blanking
Active Video
Table 10: PAL
Line Numbers
1-22
23-310
311-312
313-335
336-623
624-625
Field
1
1
1
2
2
2
Description
Blanking
Active video
Blanking
Blanking
Active video
Blanking
Black Level Subtraction and Digital Gain
Image stream processing starts with black level subtraction and multiplication of all
pixel values by a programmable digital gain. Both operations can be independently set
to separate values for each color channel (R, Gr., Gb, B). Independent color channel
digital gain can be adjusted with registers. Independent color channel black level adjust-
ments can also be made. If the black level subtraction produces a negative result for a
particular pixel, the value of this pixel is set to 0.
Positional Gain Adjustments (PGA)
Lenses tend to produce images whose brightness is significantly attenuated near the
edges. There are also other factors causing fixed pattern signal gradients in images
captured by image sensors. The cumulative result of all these factors is known as image
shading. The ASX340AT has an embedded shading correction module that can be
programmed to counter the shading effects on each individual R, Gb, Gr., and B color
signal.
The Correction Function
The correction functions can then be applied to each pixel value to equalize the
response across the image as follows:
Pcorrected(row,col)=Psensor(row,col)*f(row,col)
(EQ 1)
where P is the pixel values and f is the color dependent correction functions for each
color channel.
ASX340AT/D Rev. H, 8/15 EN
20
©Semiconductor Components Industries, LLC, 2015.