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Tim Fenn wrote:
Say you want a fig. with final resolution of ~ 300 dpi at a final size
of 4-in by 3-in.
I always notice people do this, but it doesn't actually get around the
issue of print resolution versus image resolution (and no, the two
aren't the same). Just becuase I have a 1200x900 image scaled in a
4x3" box doesn't mean my printer will use 300DPI when it prints - I've
seen cases where printers/programs actually take a 72DPI image and
upsample it to 300, then rescale it to the desired size on the page,
which doesn't look too good in print. Anyway, I've started using the
GIMP to reset my print size without affecting the image in any way.
I realize this problem has been solved by new capabilities of
pymol, but there is a conceptual problem here which is
bothering me.
If N. Stanley takes his images which are unacceptably low
in resolution, but about the right size, and uses gimp to
change them to higher resolution, he is either going to get
very small images (if gimp does not "resample" but simply
redefines the size of the pixel), or he is going to get a
picture which nominally has higher resolution and takes up
n**2 times as much disk space, but looks identical to the
original (if gimp resamples). If he wants a 4x3 picture
that really has 300 dpi resolution, he has to start with
1200x900 pixels, no matter how painful the math.
For me the primary characteristic of an image is the
number of pixels. This determines the information content,
the level of detail. You can print it at 2 ppi on a billboard
and look at it from across town, or print it on a postage
stamp and look at it with a magnifying glass, the same level of
detail is present as long as you keep the same pixels.
Some image formats (like GIF) don't even record the
image size/resolution, but leave that up to the displaying
program/device.
The publishers don't see it that way, because their presses
are designed to work at specific resolutions, and color
print-screen frequencies interact with the image frequency.
They want a specific resolution, usually 300 or 600 dpi.
The go-between is the editor (or reviewer or whoever decides
what size the picture should be). If he says "No you can't
have a full page for that figure, you have to make it
one column width" then you look up the column width and
multiply by the resolution the publisher wants to get the
number of pixels you need. Make a figure with that many
pixels, the resolution is irrelevant. Then just before you
you upload it to the publisher, convert to a format like
tiff that does preserve figure dimensions, and set the
resolution without resampling the pixels. And voila- the
size will be one column width, and all the original pixels
created by the graphics program are there.
I admit in some cases where the figure had all the detail
I felt the human eye could see at the final size,
but the resolution was 200 instead of 300 dpi at that size,
I have resampled to make the nominal resolution higher
without increasing detail.
There may even be valid reasons for doing this where the
need for higher resolution is not to show more detail but to
satisfy technical requirements of the printer. But the final
figure would have been better if I had remade it with more
pixels to start with.
Ed
