[muglo] Editing and converting Images (Was: PowerPoint

On 2005 Jan 24, at 09:11, Garth Phillips wrote:

> When pulling pix in or out of power point try saving the image in the 
> bitmap
> rather than jpg format.... While you can't manipulate them as much
> afterwards, bmp files are usually 1/3 the size of jpg. In doing this, 
> I've
> taken presentations from 20MB down to 2 or 3MB. Loads and mails lots 
> faster
> too!




Garth's comment about size and manipulability
does not match my experience.  Through experimentation,
I have found that a lot depends on the type
of picture.

I wonder what kind of picture it was that used less
space as a BMP file than as a JPEG.  I would guess that
the JPEG might have come from a camera that has lots
of pixels and you want to prepare the picture to present
well only on a screen.  If that is so, then Garth's idea
is one way you can reduce the size.  Another is to reduce
the number of pixels.  But beware, if you do either of
these things and throw away the original, forget about
making large prints some day.

Please let me tell you a recent experience.  I have a great
shareware program that I "tried" for a while before I
bought it.  It is GraphicConverter, and what it does,
it does very, very well.  (I guess this would support
Eric's idea that stand-alone products are generally
superior.)   GraphicConverter writes pictures of every
format know to (this) man.  There are 78 formats on my
version and I presume that it reads anything it can write.
I have not tried ALL the combinations!  This means that
one can manipulate any format equally well.

Now, the business about sizes of JPEG files.

I think that the size of a BMP file is determined
solely by the number of dots in your rectangle and
the depth of colour you are using on the screen.
JPEGs use a system of patterns that are more and more
finely graduated.  Depending on the quality of the
image you want, it is possible to control he number of
patterns that are given.

As an example, this morning,  pasted together
two screen shots. I was using OS X so the the files were
PDFs.  I combined and trimmed the images, and got a PDF with
        2639 3098 = 8,175,622 pixels
        32 bit colour  (what Apple calls "Millions of colours")
with a total of
1326 x 3098 x 32 =  261,619,904 bits, which is 32,702,488 bytes.
In spite of the colour depth, it was a screen shot of OS generated
things, sand it used only 3112 different colours.

I saved my picture as a PDF file.  The size was 1.9 MB
I saved it again as a BMP file.  The size?  23.4 MB.
BMP was 12 times larger than PDF for this image.

I did three JPEG experiments in which I varied the quality
of the JPG compression.  With GraphicConverter, one has a
choice for the quality of the image: any number from 0 to 100.
If I choose 100, I seem to get the best quality picture but
the compression is not so good.  If I choose 0, I get great
compression, but not good image quality.  For some pictures,
like snapshots for example, a number in the 70 range is fine.
The file might be smaller than the original from  the camera,
and the image might be good enough to put up on my screen, but
it might not look good enough in a large format printed photo.

I tested three different values: 100, 50, 0 of JPEG compression.
Each time I re-loaded the my original PDF file before I did
the save, so any changes I might have made in a previous
test were bypassed.  I got these results.

                Value: 100 (best quality)       Size: 1.769 MB.
                Value:  50 (mid level)          Size: 0.406 MB
                Value:  -0 (low quality)                Size: 0.097 MB

Conclusions:  You can not generalize about the size of a JPG file.
I have one example where the BMP is 12 times as big as the PDF file.
The BMP is 60 times larger than an acceptable, mid-level JPG.

Your experience may vary depending on the quality of the image you
start with, what level of detail you want, what screen depth you
are using, and whether or not you think you will ever want to
make a large print.

   If you are interested in small pictures and you don't
want large prints, it does not matter much which format
format you use.  If you can't see the difference with
your own eyes, don't worry about it.

Personally, I want more from my next camera.  I want it to give
me the option of an image in "raw" format, as it comes from the
sensing module, because raw image has the potential to be enlarged
beyond the level where other formats images would break up into
annoyingly large pixels.

Lee

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