On 02/10/2013 02:31 AM, Frederic Da Vitoria wrote:
2013/2/10 Gnome Nomad <gnomeno...@gmail.com <mailto:gnomeno...@gmail.com>>
I just did a test with a jpg original, it lost 50% size with
compressed
tiff besides uncompressed tiff. But maybe a jpeg image lends
itself well
to compression.
JPEG compresses by *throwing out parts of the image* like MP3 and
other audio formats. It is a LOSSY compression method. What they
throw out is determined by psycho-perceptual studies that showed,
"We can throw this out because the average human eye/ear doesn't
really perceive them very well." TIFF doesn't lose any parts of the
image.
When you uncompress a TIFF, you get back the exact image you compressed.
When you uncompress a JPEG, you get back something that "looks" like
the uncompressed image, but isn't an exact match.
Yes, I know this. What I meant is that a JPEG image has much less data
in it than for example a RAW image, precisely because JPEG compression
throws out data. IIUC, one of JPEG's ways of compressing data is
restricting the colour palette locally. It seems intuitively plausible
that a JPEG image would lend itself better to LZW compression, because
the colours variety would be locally poorer than in a RAW and this would
make LZW more up to the task.
Possible. I don't know how LZW works in that conjunction. Or even what
algorithm JPEG uses after it's thrown out "unneeded" image data.
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