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Re: Help with jpeg image problem

> -----Original Message-----
> From: adavis@ubasics.com
> Sent: Wed, 3 Oct 2007 21:32:04 -0400
> To: ejr@inbox.com
> Subject: Re: Help with jpeg image problem
> This is not uncommon for the type of conversion you're doing.  If you
> don't
> want the banding to occur you'll need to implement a dithering algorithm
> of
> some sort.
> As far as the single pixels changing from one image to the next (even
> though
> it's the same picture) keep in mind that even one bit changes in the 24
> bit
> color can change the last bit in the 16 bit color.  Given that each image
> has thousands of pixels, it's likely that a few, or several, are right at
> that transition point and even though you say the image is the same they
> may
> be slightly different and transition to the other color.  I don't have
> any
> great solutions for this, unless you can modify the output of the JPEG
> encoder.  An averaging (filter) algorithm might help here, and a general
> blur with dither will certainly calm the image down at the expense of
> clarity.
> Lastly, double check your setup - many 16bpp LCDs actually use 565 RGB -
> the
> green has 6 bits.  This may alleviate your banding somewhat if your
> design
> has that extra bit.

Thanks for your response. I've only designed the hardware for 555.
The dither algos didn't do anything but I'me leaning more to the encoder


> On 10/2/07, Junior <ejr@inbox.com> wrote:
>> Hi,
>> I'm not sure if anyone can offer any advice but it doesn't hurt to try.
>> I'm using libjpeg to decode a jpeg image stream. My hardware is a 555
>> 16bpp ARM9
>> (65535 colors) and the image header reads 24bpp RGB and I'm assuming
>> that's 888 format.
>> When I decode the image, I see the gradient change which I didn't expect
>> even for a
>> grayscale image.
>> I'm doing everything the docs says and followed the examples with the
>> only
>> difference
>> being I'm only using the upper 5 bits.
>> In addition to seeing the well defined color change gradients, I'm
>> seeing
>> a lot
>> of the image changes pixel values. For example is goes from darkgray to
>> lightgray from one
>> stream to the other, although the image has not changed.
>> Has anyone worked with this library and seen this before? Any ideas?
>> Thanks,
>> --Jr.
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