Specifications

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1.3. JPEG ENCODER/DECODER
The CL765 has a fully-hardwired JPEG codec. It encodes an image incoming from
CMOS/CCD image sensor, and decodes a JPEG stream sent from Host CPU.
During the encoding/decoding, various image processing like scaling, image
effects are pre/post-processed by using dedicated hardware blocks.
1.3.1. JPEG Encoding
The CL765 encodes an image either from camera sensor (this function is called as
JPEG capture) or stored in frame buffer into JPEG stream (this function is called as
BMP2JPEG). The data format at input stage of JPEG encoder is 4:2:2-YCbCr. The
format of data from camera sensor is 4:2:2-YCbCr, and hence the image from
camera can be encoded without data format conversion. For images in frame
buffer, not only the video image but also OSD image, they are mixed into one
image in RGB color space, converted to 4:2:2-YCbCr format and sent to JPEG
encoder. Before JPEG encoding, the original image is resized and translated
through dedicated hardware scaler and image effecter, respectively.
The encoded JPEG stream is stored into internal memory and transmitted to Host
CPU. The CL765 uses so-called flow-control scheme to transmit encoded stream
to Host CPU. In short, the scheme permits Host CPU to read on-making JPEG
stream simultaneously with JPEG encoding. The scheme eliminates image size
limitation in JPEG encoding, and hence Host CPU can capture larger size (up to
3M pixel) image than the CL765’s internal memory.
1.3.2. JPEG Decoding
The CL765 decodes a JPEG stream from Host CPU, and stores the result 4:2:2-
YCbCr image into its Video Buffer. The stored image can be displayed on output
visual devices (LCD or TV) or can be transmitted to Host CPU. Before storing the
BMP into Video Buffer, the CL765 (optionally) resizes and translates the decoded
image by using scaler and image effecter.
Like the encoding operation, decoding operation also uses the flow-control
scheme. In this case, JPEG decoder decodes JPEG stream while Host CPU writes
the JPEG stream into the CL765’s internal memory.
1.3.3. Image Scaling and Effects
As described above, the CL765 has a dedicated hardware scaler and an image
effecter. The scaler is used for image scaling and digital zoom. The zoon-in and
zoom-out can be supported up and down to 4X and 1/16X, respectively. The scaler
uses multi-tap image filter to reduce artifacts caused by scaling, and hence keeps
high quality of resulting image. The image effecter consists of various image
profiler and filters such as edge detector, hue compensator, gamma corrector, etc.