Digital Photography Hacks [Electronic resources] نسخه متنی

Hack 28 Analyze Metadata to Improve Your Shots

In the days of film cameras, I seldom recorded
exposure settings that would have helped me better analyze my
pictures. Now, digital cameras handle all that work for me, and I can
use that information to figure out what went right or what went
wrong.

Every time you click the shutter, your digital camera records
valuable picture data that describes the image you just captured.
Data such as time, shutter speed, aperture, focal length, and ISO are
written to the file header in the Exchangeable
Image File (EXIF) format. This information becomes part of the total
image file and can be displayed with applications such as Photoshop.

In essence, each picture file contains a complete photographic
history of the decisive moment, which can be analyzed to help you
understand why the image was successful or give you clues as to what
went wrong. In this hack, I'll show you how to
retrieve this data and use it to hone your photography skills.

2.14.1 What Is EXIF?

The EXIF format
is an international specification, first established in 1995, that
enables digital cameras (and other imaging devices) to write data to
the file header of the image. EXIF files use the JPEG DCT format
specified in ISO/IEC 10918-1. The picture portion of the file can be
read by any application supporting JPEG, including web browsers and
image editors. The metadata can be accessed by applications designed
to extract that information out of the header and display it. The
most common imaging applications have no problem displaying at least
some of the EXIF data.

However, the picture file usually contains more information than
what's typically displayed by a given application,
unless that application is designed specifically to output EXIF
information. For example, iPhoto on the Mac provides the basic time,
date, file size, and camera information when you click on the Photo
tab of the Show Info window. If you click on the Exposure tab, you
get more data, such as shutter speed, aperture, focal length,
exposure compensation, metering pattern, and flash status.

But iPhoto doesn't provide you with other data
sitting there in the file header, such as white balance. If you need
that information, you have to open the file with another application
designed to grab that data. The point is that the EXIF specification
dictates what goes in to the picture file, but image editors
typically give you only a portion of that information. So, if you get
serious about reading this stuff, you might need to add a couple
tools to your imaging bag of tricks (more on this later).

2.14.2 Why Would I Want to Read EXIF Data?

When you take
pictures, some turn out better than others. Why is that? Beyond good
composition and subject matter, there are many factors that
contribute to powerful images. These include time of day, depth of
field, proper shutter speed, and exposure compensation as needed.

If you look at a picture of running water, for example, and you like
the way it's rendered, wouldn't it
be nice to know the settings that you used, so you could duplicate
the effect? Before digital cameras were available, I would take
handwritten notes to help me remember the settings for particular
shots. I hated that! Now, the camera records all that information for
me, and I'm free to concentrate on taking good
pictures.

I know that I can control the way water appears by adjusting the
shutter speed. The 1/250-of-a-second exposure
"stopped the action" to some
degree, and the 1-second exposure created a soft look. Now, the next
time I shoot running water, I can capture the exact effect I want by
adjusting the shutter speed.

Time of day also has a dramatic impact on pictures. (Make sure you
have your camera's time and date settings correct so
that they are accurately recorded with the picture.) Over the course
of a few hours, a scene can totally change in appearance. When I
checked the metadata for Figure 2-22 in iPhoto, it
said that the image was captured at 10:45 a.m. The shot in Figure 2-23, from roughly the same location, was captured
at 8:15 a.m. the following day and was rendered much differently.

Even though these pictures were captured from roughly the same
location, only a day apart, they are very different. The sun was
higher in the first picture and it flattened out
the scene, rendering more even highlights and shadows. The same
picture shot two and a half hours earlier on the following day shows
the difference when the sun is lower and creates harsher highlights
and shadow areas.

If I were to go back to these lakes at the same time next year, I
could then determine what time to start shooting based on my review
of the metadata for the pictures I'd already taken.
If I wanted more even, less dramatic lighting, then late morning
seems ideal for that effect. On the other hand, if I like the harsher
contrast of darks and lights, then I know I have to get there a few
hours earlier.

Figure 2-22. The lake at 10:45 a.m.

Figure 2-23. The lake at 8:15 a.m.

These are just a couple ways to review EXIF data to analyze your
pictures. Other settingssuch as flash on or off, exposure
compensation, white balance, and aperture setting (for depth of
field)are all important clues to understanding the success or
failure of your images.

2.14.3 What Should I Use to View EXIF Data?

You have many
options for viewing the EXIF data your camera captures. As I
mentioned before, digital shoeboxes such as Adobe Album, iPhoto, and
iView Media Pro provide you with most of the important information
that you commonly need. Also, take a look at the software bundled
with your camera. For example, both Nikon and Canon provide image
utilities that are pretty good at displaying the data your camera
captures. A good universal tool is Photoshop Elements, which can
serve as your full-featured image editor and can show you all of the
metadata you'll ever need to know via the File
Browser function (WindowFile Browser). Figure 2-24 shows an example of the type of information
you can get from Photoshop's File Browser.

Figure 2-24. Viewing EXIF data in Photoshop's File Browser

This application shows me settings, such as white balance, that
aren't displayed in more basic image editors. I
don't always need this level of detail, but
it's nice to know it's there if I
want it.

2.14.4 Final Thoughts

I recommend you keep a set of original files for all of your
important images. In part, I think this is just good file management.
But I also like to have those original pictures because I know that
the metadata will be intact for me to review whenever I want it.

When you manipulate pictures and save them in optimized formats,
important metadata is sometimes removed from the header. If you
don't have those original files to fall back on, you
might lose that information forever. Plus, it's
always wise to have the unaltered, uncropped picture stashed away
safe and sound.

This hack just scratches the surface of metadata use. Soon,
GPS-equipped cameras might be able to record positioning coordinates
to the EXIF file, which could later be translated into locations when
browsed with the image editor. Who knows what else? But for now,
tapping EXIF data can certainly help you take better pictures and
serve as a permanent record for when you recorded them.