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Alfred wrote:
> For example, lets say you have a 100 Kb GIF file. What I am looking
> for is the equivalent file size in PNG and JPEG of the same file
> when converted?
There are two issues complicating this.
(1) As you mention, there are different levels of compression within the file
formats. This affects file size dramatically. How big is a 100K GIF converted to
JPG? Depends on what quality you need.
(2) More importantly: You probably wouldn't want to convert that GIF to JPG. If
it's line art, or a screen shot, or some other image without subtle gradations
of color, GIF works better; JPG would only make the lines blurry. If it's a
photograph, it shouldn't be in GIF format in the first place. Ideally you'd want
to get the source file and then save to JPG. (I don't know much about PNG,
except that it's an open-standard alternative to GIF.)
I can't think of a reason to save a GIF as a JPG or vice versa, except in cases
where it was saved in the wrong format to begin with. And in those cases,
converting wouldn't help. A screenshot saved to a low-quality JPG is toast, and
converting it to GIF won't bring back the clarity that has been lost. A
photograph saved to a low-quality (i.e., lower # of colors) GIF will be sort of
posterized; a 3-D object would look a bit like a topographical map. Saving that
to JPG would only blur it. (If you're working with higher-quality images, you
can get away with converting sometimes, but it's always preferable to work with
the uncompressed source image instead.)
You can't reassemble a potato from a puree and then make french fries out of it.
As an experiment, I took one of the Photoshop sample images (ducky.psd) and
saved in various formats. This won't tell you anything very useful, but here are
the file sizes:
Original: 711k
PNG: 321k (I suspect I could've reduced the file size if I had tweaked the
options when saving as PNG)
GIF: 256-color, 76k. 16-color <shudder>, 21k.
JPG: highest quality, 179k. Lowest quality, 17k.
(For that particular image--a photograph of a rubber ducky--I would go with a
medium-quality (7) JPG, at about 32k.)
HTH,
Christine
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