Hi Derek,
If we turn the auto exposure on, the frame rate will drop from 13fps
to 3fps in an indoor environment. But if we change to manual exposure
and use a low exposure. Then the frame rate will be back to 13fps but
the image will be dark again. The exposure value in the code is
exactly how much time the image sensor will wait between two frames
(the value is measured by rows). The windows driver shows a poor image
with high frame rate. I guess they use a low exposure, acquire a dark
image then light it by software.
Sorry about the pixel format. But I'm not interested much at the pixel
encodings now. I only intend to use the camera in my own java
application. And I only need the raw unprocessed 1280x1024 Bayer GRBG
data. The raw data which is generated directly by the sensor pixel
array consists of 1280*1024 8-bit values. Each value represent only
one color in the following sequence,
G R G R ...
B G B G ...
....
But after we process it to a color image, we lost the precise pixel
location. So the raw image is more valuable although it can't be seen
directly. I wrote a JAVA function which can convert Bayer data to a
color image, in this function the missing colors are calculated by the
two or four nearest pixels which represent the same color.
public static void decodeSBGGR8(int width, int height, byte[] bs,
int start, BufferedImage image) {
boolean evenRow = true;
int[][] is = new int[width + 2][height + 2];
for (int y = 0; y < height; y++) {
for (int x = 0; x < width; x++) {
is[x][y] = bs[y * width + x + start] & 0xFF;
}
}
for (int y = 1; y <= height; y++, evenRow = !evenRow) {
boolean evenColumn = true;
for (int x = 1; x <= width; x++, evenColumn =
!evenColumn) {
int data = is[x][y];
int lr = (is[x - 1][y] + is[x + 1][y]) >> 1;
int tb = (is[x][y - 1] + is[x][y + 1]) >> 1;
int r, g, b;
if (evenRow) {
// G R
// B G
if (evenColumn) {
r = lr;
g = data;
b = tb;
} else {
r = data;
g = (lr + tb) >> 1;
b = (is[x - 1][y - 1] + is[x +
1][y - 1]
+ is[x - 1][y +
1] + is[x + 1][y + 1]) >> 2;
}
} else {
// G R
// B G
if (evenColumn) {
r = (is[x - 1][y - 1] + is[x +
1][y - 1]
+ is[x - 1][y +
1] + is[x + 1][y + 1]) >> 2;
g = (lr + tb) >> 1;
b = data;
} else {
r = tb;
g = data;
b = lr;
}
}
int rgb = 0;
rgb = (r << 16) + (g << 8) + b;
rgb |= 0xFF000000;
image.setRGB(x - 1, y - 1, rgb);
}
}
}
The driver defined the following pixel format,
V4L2_PIX_FMT_SBGGR8,"Bayer 8bit (BGGR)", 8,0x2d
V4L2_PIX_FMT_YUV420,"I420 (YUV 4:2:0)", 12, 0x2f
V4L2_PIX_FMT_YUYV,"YUYV (YUV 4:2:0)", 16, 0x2e
V4L2_PIX_FMT_JPEG,"JPEG (YUV 4:2:2)", 16, 0x2c
If we choose a format, the driver will write the value in the last
column to the bridge register 0x10e0. (For example, write 0x2d for
V4L2_PIX_FMT_SBGGR8 format). For JPEG format, the driver will attach a
JPEG header to the data. But the JPEG image doesn't seem to be right
at colors. For other format, the driver will directly send the data
from SN9C202 to applications. I guess most application will use the
V4L2_PIX_FMT_JPEG format so the color is not right.
Most problems of MT9M111 sensor have be solved by now. Today I found a
bug at the function sn9c20x_set_resolution, the line
clrwindow[4] = ((mode->width >> 10) & 0x01) |
((mode->height >> 10) & 0x06);
should to be changed to
clrwindow[4] = ((mode->width >> 10) & 0x01) |
((mode->height >> 8) & 0x06);
Otherwise in 1280x960 and 1280x1024 mode, SN9C202 will only return
1280x0 and 1280x0 image. Besides this,
we also need to tell the image sensor MT9M111 to switch to full
resolution mode by adding the following code. It switchs the sensor to
a predefined context. We can also set other registers to tell the
sensor to not skip rows and columns. But switching context is easier.
int data;
if (mode->width==1280) {
data=0x170F; // Context B output 1280x1024
sn9c20x_write_i2c_data16(dev, 1, 0xC8, &data);
} else {
data=0x0004; // Context A output 640x512
sn9c20x_write_i2c_data16(dev, 1, 0xC8, &data);
}
I can get 1280x1024 image from WebCam now. It's very close to make
MT9M111 fully supported.
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