Depth of field
Tip 7: Use a photo editor (but use it sparingly!)
You will dramatically improve your photography if you use a photo editor to crop your images and to adjust the image slightly.
I use the Gimp, a freely distributed photo editor that rivals expensive commercial products
such as Adobe Photoshop. The gimp offers advanced features including layers, masks, filters, scripting, cloning, color correction,
and more. The Gimp is available for Unix,
Macintosh OSX, and Windows operating system; I've found that it works
smoothly on all three platforms. The on-line book Grokking the Gimp
provides a detailed tutorial covering many of the Gimp's features.
What can a photo editor do for you? Here's a rather extreme example. I've started with an unusually bad initial photograph, and corrected it with a few simple steps.
Let's go through these steps in detail.
- Adjust the angle. The original photograph is off from horizontal by about one and half degrees. I've rotated the image back one degree to compensate. The gimp offers a "corrective" rotation tool; you simply align the rotation grid with a strong horizontal or vertical line in the image:
- Crop the image. After rotating, I've cropped the image to a
more appropriate size. I find it easier to shoot an overly-large frame
and then crop down than to try to select the exact frame when taking
the photography. This also give me latitude for angle adjustments, as
If you plan to share your image on the internet, crop
relatively tightly, so that you can make best use of the photo size. If you
are photographing a vertical display, crop to a vertical (portrait) frame.
Crop a horizontal display to form a horizontal (landscape) frame. And always
be sure to leave enough background around the tree that it feels balanced
and naturally positioned within the frame.
- Adjust the intensity levels. The initial photograph
is washed out, the backdrop is grey, and a lens flare glares on the
right side of the tree. By adjusting the intensity levels of the
image, I'm able to get a black backdrop and crisp, saturated colors
that you see in the final image. (Because I started with such a bad
initial image, this comes at the expense of a slightly unnatural color
to the basecloth. Had the initial image been properly exposed, much
less correction would be required.)
To adjust intensity levels, select Image: Colors: Curves from the Gimp menus. This brings up a dialog box as shown below. Adjust the "value" channel. To correct the sample image here, I used the following curve:
For a properly exposed black backdrop, I use a more "neutral" curve such as the following:
- Resize and compress the image. If I plan to share an image
over the internet, I want to resize it and compress it to a small file
size, with minimal loss of image quality. I don't want to lose my
original large-size, uncompressed image files, so I always save under
a new name when resizing and compressing.
For sharing on the net,
you want the image to appear comfortably within a web brower or email
program. To ensure this, I typically resize an image to be no larger
than 600-800 pixels along its longest dimension. (800 pixels is
actually a bit too tall to fit onto most browser screens at 1024x768,
so you might want to restrict the vertical size to 700 pixels or
When sharing photographs on the net, you also want to keep file
sizes small, and this requires some compression. Most internet sites
will accept photographs no larger than 50 or 70 kilobytes. To compress
your image to this size, save it image as a JPEG file at about 75%
quality; this automatically compresses the image file without too much
loss of detail. Certain images may need to be saved a higher quality
to look good; play around and see what works for you.
Use your photo editor sparingly. I tend not do much else in the photo
editing program. I don't like to retouch my images using the clone
tool or to snip stray leaves using an airbrush. For me, that crosses
the line from photograph to virtual image. Similarly, I don't like to
augment the color saturation or shift the color balance. You can get
really stunning autumn colors that way, but I don't think it's
worthwhile. Partly, I want to record and represent the tree as close
to accurately as is possible within the bounds are artistic necessity;
partly, I prefer nature's subtlety to the pop of digital
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Last modified December 29, 2004
Copyright © 2004 Carl T. Bergstrom