[sane-devel] backend Kodak i260 Image depth 48 bits stream. How is coded?

[m. allan noah]

attached is a simple program that extracts the image, but does not
properly do the colorspace conversion. i tried the algo that you
found, and another that i found, but they both seem to take the blue
data out of the 0-255 range, so i guess you have to clamp the values.
also, this code uses the same Cr and Cb for all 4 pixels, it should
probably be interpolated with the next Cr and Cb values.

allan

On Sat, Aug 30, 2008 at 8:52 PM, m. allan noah <kitno455 at gmail.com> wrote:
> thanks daniel- now this begins to make sense:
>
> http://wiki.multimedia.cx/index.php?title=YCbCr_4:2:0 says:
>
> "Since 6 bytes, or 48 bits represent 4 pixels, an average of 12 bits
> are required to represent a single pixel in this scheme."
>
> so the 48 bit depth in the set window command is for each 2x2 block.
>
> i guess they dont put all 4 Y samples together cause they are on
> different scanlines.
>
> if you look at the slope on the edge of the taillight you can see that
> each pair Y samples are switched, as you have stated.
>
> allan
>
> On Sat, Aug 30, 2008 at 5:54 PM, Daniel Glöckner <daniel-gl at gmx.net> wrote:
>> The picture is in YCbCr 4:2:0 format.
>>
>> 0. byte: Y(1,0)
>> 1. byte: Y(0,0)
>> 2. byte: Cr(0.5,0.5)
>> 3. byte: Cb(0.5,0.5)
>>
>> 4. byte: Y(3,0)
>> 5. byte: Y(2,0)
>> 6. byte: Cr(2.5,0.5)
>> 7. byte: Cb(2.5,0.5)
>> :
>> :
>> 4796. byte: Y(2399,0)
>> 4797. byte: Y(2398,0)
>> 4798. byte: Cr(2398.5,0.5)
>> 4799. byte: Cb(2398.5,0.5)
>>
>> 4800. byte: Y(1,1)
>> 4801. byte: Y(0,1)
>>
>> 4802. byte: Y(3,1)
>> 4803. byte: Y(2,1)
>> :
>> :
>> 7198. byte: Y(2399,1)
>> 7199. byte: Y(2398,1)
>>
>> repeat for the following 7200 byte blocks
>>
>> The chroma offset is guessed.
>> It would need some sharp colorful edges to verify that.
>>
>>  Daniel
>>
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>
>
>
> --
> "The truth is an offense, but not a sin"
>



-- 
"The truth is an offense, but not a sin"
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