10
PL-A780 Camera Specifications
Document No.: 04646-01
PixeLINK PL-A780
MACHINE VISION CAMERA
SYSTEM GUIDE
Copyright © 2004 PixeLINK
All Rights Reserved
Figure 5 Color Bayer Pattern - Pixel Addressing Mode 6 (Decimation 6x)
The sensor ROI can also be resampled to combine the signals from a 2 x 2 or larger block of
pixels (GRBG) into one RGB triplet. To see how this has an effect, it is important to
understand that, for all other modes, the camera converts the Bayer pattern from the sensor
into RGB triplets for each pixel, taking the missing values of the triplet from the surrounding
pixels and creating three times the amount of image data. These RGB values are then color
corrected and processed before being converted to the selected output type or Color Coding
(see Section 5.1.3.2 on page 31) for transmission to the host. When the output type is Raw
or Bayer, the RGB image data is converted back to Bayer by dropping two thirds of the data
and only transmitting the remaining third as a Bayer pattern. At the host, the Bayer pattern is
converted back to RGB for display. The Bayer to RGB conversion uses algorithms that have
an effect similar to smoothing filters and image detail is slightly blurred each time the
conversion is performed.
When outputting in YUV422, no Bayer to RGB conversions are performed at the host. All the
intensity information is transmitted along with half the color information of the RGB image.
The resulting transmission uses more bandwidth and the frame rate will be reduced but the
image will have more detail.
By combining blocks of pixels to one RGB triplet, resampling does not use data from
neighboring pixels so no smoothing occurs. Resampling effectively reduces the image
resolution and increases the pixel size. Resampling also results in sharper image quality
compared to decimation or averaging which are affected by the Bayer to RGB conversions
discussed above. For the best results, the output type or Color Coding should be set to
YUV422 when using resampling.
Figure 6 below shows the effects of the various modes of Pixel Addressing on image quality.
The images are of a Nyquist chart. Figure 6 a. shows the full resolution image with no
decimation, averaging or resampling. The colors that appear in the chart are a result of the
Bayer pattern. They occur when the fine lines in the chart cover certain colors in the Bayer
mosaic on the sensor. The regular patterns in the Nyquist chart exaggerate the effect. The
appearance of the colors is an indication of good focus in the image, but they do detract from
