RE: Which image format

["Bill Lawrence" <scribe -at- matrixplus -dot- com>]

I've been doing a lot of research into this lately because, aside from
technical writing, I do other sorts of nonfiction.  I'm currently
working with hundreds of historical photographs and I needed to
understand what graphics formats are lossless and yet have decent
compression.  Also, fortunately, our head of software engineering used
to work in the digital graphics field and provided some additional
insights.

For really high quality reproduction, you want to select a format that
looses no data.  Because of the nature of the JPEG format, believe it or
not one loses data just in the process of encoding an image into JPEG
(even in its so called "lossless" form).  JPEG2 does a better job, but
nobody supports it.

GIF is always a bad choice, simply because of the color depth
limitations.

That leaves TIFF, BMP, and PNG.  As someone pointed out, bits-are-bits
at this stage.  TIFF is well supported by professional level tools.  PNG
has the advantage of being viewable by most web browsers as well.  PNG,
like JPEG, has a variable compression-vs-image loss capability; however,
its lossless form is truly lossless and its file sizes are smaller than
the other two formats.

Here's a trick you might be able to use: Our technical documentation is
single-source with both PDF and HTML as deliverables.  Because our PNG
files are rather large (both in file size and in the amount of space
they take up on an HTML page), we batch convert the super-high quality
graphics for print to make them more suitable for online viewing.  We
scale them, increase the compression, and also set them all at the same
DPI.  Setting them to the same DPI is important because sometimes we get
graphics generated by other tools and this eliminates surprises when
viewing the graphic through a web browser.  We use a tool called
nconvert, which you can download from the web.

Bill Lawrence

Senior Technical Writer
Matrix Solutions