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Re: [Spca50x-devs] Need Help: Number_of_Image Data Bytes_Clarification




Le Mercredi 14 Novembre 2007 06:11, George Neil C a écrit :
> Hello,
>
> I am trying to interface a webcam to AVR USB Microcontroller. The webcam is
> having an SPCA561 bridge,
>
> I try snooping the image data while connecting the webcam to PC, then i am
> getting image data as Isochronous packets.
>
> There are 32 Isochronous packets of 896 bytes each obtained in one stretch,
> out of which there are
>
> 1) some NULL packets [First Byte 0xFF]
>
> 2) A start of frame packet [First Byte 0x00]
>
> 3) Then another 22 packets [First byte 0x01 to 0x16]
>
> 4) In between random occurrence of NULL packets [First Byte 0xFF]
>
> 5) After the last packet [First byte 0x16] the start of frame packet [First
> Byte 0x00] re-appears.
>
> Which means the valid bytes for a FRAME = 23 * 896 bytes = 20608 bytes
>
> But the expected number of bytes for a FRAME
>             = Total no of pixels * No.of bytes per pixel
>             = [352 * 288] * 3
>             = 304128 bytes
>
>
>                 [where resolution = 352 X 288
>                 compression = RGB 24 , ie 3 bytes per pixel]
>
> Then please explain how the full image[304128 bytes] is produced from just
> 20608 bytes..!!
If the chips is set in compressed mode, you need to ask Sunplus for the 
proprietary compressor.
In uncompressed mode the stream is from a  Bayer pattern and so
a frame is (height x width) = size
-- 
Michel Xhaard
http://mxhaard.free.fr

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