Compression - Re: [Question] Does JPEG specification define thumbnail image generation

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Re: [Question] Does JPEG specification define thumbnail image generation

jim

2006-09-05, 6:55 pm

George Wilson wrote:
>
> Questions
> 1. Does JPEG specification define thumbnail image generation for JPEG
> images?
> if so any references on web.
>
> 2. How thumbnails are generated for high resolution JPEG images and
> placed as part of the JPEG file?
>
> Any relevant information will be appreciated.

It is possible to easily and quickly extract thumbnails that are 1/2,
1/4 or 1/8 the size of the original. This is due to the structure of the
data. It isn't rally part of the jpeg specification as far as I know.
I's just that the low frequency content is already computed and stored
for those particular resolutions.

-jim

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