MaximumPC 2008 12

PICTURE

PERFECT

Make Levels Adjustments

Expose a picture’s hidden details

E

ven with cameras that compensate

for white balance, lighting condi-

tions, and available color range in

a composition, you can still end up with

under- or overexposed images or a color

cast. In ideal circumstances, you’d correct

the problem at the time of shooting, but

GIMP’s Levels tool lets you do some reme-

dial work on an existing picture. The most

useful application of the Levels tool is to cor-

rect underexposure, which the walkthrough

below demonstrates. It may be possible to

reveal more detail without producing a harsh,

overly contrasted image. You may also be

able to undo a color cast without saturating

the image with the contrasting color. The

screen to the right shows the main controls

available in the Levels dialog.

STEP BY STEP

Fix an Underexposed Image

Just as you can use the white dropper to point

to part of the image that should be white, you

can also select the black dropper and choose a

point that should be black.

CHANNEL

This drop-down

list lets you select

one of the three

main color chan-

nels to adjust: red,

green, or blue. Al-

ternatively, leave

it set at Value to

change all chan-

nels at once.

INPUT LEVELS

The bottom axis

represents the

color (zero to 255)

with the vertical

axis showing the

frequency at which

that tone appears.

AUTO

Click this button to automatically balance the

levels in the image or selection. It’s the best way

to get an acceptable improvement, but the result

can look harsh if the tool is used on its own.

WHITE DROPPER

Use this to select an area of an image that

should appear white if all channels are

selected. If a single color is chosen, use this

tool to point at an area of full saturation

1. OPEN LEVELS
   Launch GIMP and
   open the image
   you want to edit.
   Choose Colors

   
   

   Levels to open
   the Levels dialog.
   Ensure that the
   channel is set
   to Value. This
   image shows the
   input levels at the
   lower end of the
   spectrum.
   3. REDUCE THE
   SHADOWS The
   result can look a
   little harsh and
   still hide details.
   To improve it, we
   can reduce the
   shadows. Click
   and drag the
   middle arrow on
   the Input Levels
   slider to the left.
   Other details
   should become
   more apparent.

   
   

   
   


2. TWEAK THE LEVELS
   Finally, we need to deal with the harsh tones that the automatic
   white balance produced. Move the left-hand arrow on the slider
   to the right. This should make the whites more natural. When
   you’ve fi nished tweaking levels, click OK.


3. WHITEN THE
   IMAGE
   Click the white
   Eyedropper tool
   and point to an
   area of the image
   that should be
   white. Notice
   that the cursor
   now resembles a
   dropper. Click the
   point that should
   be white and watch
   the image lift to
   match the new
   white value.

52 | MAXIMUMPC | DEC 08 | http://www.maximumpc.com

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