PHOTO: Digital Images

Sterling asked:

> With digital photography, do you not have
> the ability to play with your depth of field? Thanks
> in advance.

And Dennis Kramb answered:

>
Whenever I try to take a low-setting photo of my flowers, it *NEVER* comes
out in good focus...no matter how hard I try.  But when I do a high-setting
photo it comes out great.  So then I just reduce the dpi on the
high-setting photo to reduce the file size down to around 40~50 Kbytes.

It's a round-about way of getting a high-quality image at a reasonable file
size.<

An appropriate solution!  But to understand why, it may help to think in
terms of resolution instead of focus. 

    Low-quality = large pixels & small storage size. 

    Medium-quality = medium pixels & medium storage size.

    High-quality = small pixels and large storage size.

If the details you're trying to focus on are too small compared to the size
of the pixels -- like a flower pattern -- the image will be fuzzy. 
Although it looks much like one that's out of focus there really is a
difference.  In an out-of-focus image, some portion at a particular
distance from the camera is actually in focus -- it's just not the distance
intended.  In a digital image taken at too low resolution, however, even
the part that IS in focus will not be truly clear. 

In case that's too technical, perhaps a few very different examples will
help:

1.   Consider aerial photos with 1-yard resolution.  You can easily spot
roads on them.  You can see patterns of houses and probably even recognize
your own.  But if you're searching for cemeteries they are helpful only in
spotting abandoned roads and old clearings.  Tombstones simply have too
small a cross-section to show up on the images.  It doesn't matter how much
you enlarge one of these pictures -- if the feature you are interested in
is smaller than a pixel, it is LOST.

2.   Remember the old dot-matrix printers?  They had such low resolution
that you could easily see each dot in each letter.  Today's high-resolution
laser jets & ink jets also form letters using dots of ink -- but I can't
make out the individual dots even with a magnifying glass, can you?

3.   Ever scan conventional photos?  If the resolution is too low, they
come out fuzzy at best.  Jagged at worst.  And they can NOT be fixed.  If
you want a clear image you must rescan one at the appropriate resolution.  

So Dennis has come up with the traditional solution:  If you record an
image at high resolution, you have maneuvering room to edit it to
acceptable quality & storage requirements.  

Sharon McAllister
Who fought resolution problems during development of the Moon Program's
Rendezvous & Landing Radar  waaaaaay back when....

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