6.5 A Case Study
This chapter has covered many elements of photo touchup and
enhancement. To put all the elements into perspective, this section
presents a case study to illustrate the work flow of a typical
sequence of corrections. The photo in
is the subject of the study; it is a difficult case because it has
Before we begin, several observations can be made concerning this
- It is dark and clearly underexposed.
- The colors are muddy and there is an overall lack of sharpness.
- The photo has a green tinge or color cast to it.
- There is an unsightly bright green spot on the lefthand side of the
photo that will blemish the final product if not removed.
The subject matter, the cowboy roper with the children, is
poorly separated from the background.
In a nutshell, this photo needs a lot of help. It will be
significantly enhanced by the steps described in the rest of this
The first step, as described in Section
6.1, is to
maximize the tonal range of the image.
This is done by opening the Levels tool and choosing Auto
Tonal Range Maximized and Midtones Adjusted with the
Levels Tool: (a) Original Image and (b) Result of Levels Tool
shows the result. Figure
(a) shows the
original image for comparison purposes. In addition to selecting Auto
Levels, the midtone slider control in the Value channel has been
adjusted to lighten the result a bit. Notice that the green color
cast has been greatly diminished by the Levels
and the colors seem much clearer.
The second step is to correct for any remaining color
casts. As described in
6.2.2, this is accomplished using the Color
Picker to measure neutral colors in the
image. The cowboy trick-roper and children are standing on a stone
surface that appears to be granite. It is reasonable to guess that
this stone should be a neutral gray.
With the Color Picker, you can see that there are actually a
range of values from shadows to midtones in this stone. Measuring the
image colors at several locations yields a representative shadow value
59R 49G 42B in the dark stone just to the left of the roper's
lower legs. Similar measurements made in the lighter stone just
beneath the little boy's feet yield a midtone value of
109B. From these two measurements, it seems there is a brown/orange
cast to the image. As for a representative highlight value, the right
rear part of the lasso loop should be neutral but is measured at
177R 183G 167B. This is a pale green.
To remove these color casts, the Curves tool is used as
described in Section
6.2.2. For this case study, the
shadow values of red at 59 and green at 49 are both moved to match the
blue at 42. The midtone values of green at 120 and blue at 109 are
both matched to the red at 119. Finally, the highlight values of green
at 183 and blue at 167 are balanced to the red at 177. The result is
shown in Figure
Color Cast Correction with Curves: (a) Previous and (b)
Color Corrected Image
In comparing this image to the previous one, shown again in
(a), the stone is now clearly a more
neutral gray. Also, you can see that the skin tones had a slight
orange tinge, which has been removed.
The next step is to remove the green glint at the middle left side of
the image. This is done as described in Section
using the Clone tool. The image without this blemish is shown
Blemish Removed with Clone Tool
At this point in the sequence of corrections, it should be clear that
you cannot get additional subject detail using the methods from
6.2.6. The cowboy and children already fill the
entire range of tonal values from the darkest shadows in the cowboy's
shirt to the brightest highlights in the rope and the little girl's
collar. The only way to get more out of this image is to try and
separate the subject from the background, which can only be
accomplished by making a selection.
Selection of Background
shows the selection that was made using the Bezier Path
The selection was made in several stages. The main outline of the
subject was made first. Three regions were then removed from this
first selection by using the method for subtracting selections described
. These regions are the two
enclosures the rope makes with the roper's body and the small hole
between the roper's and little girl's leg.
Inverting the selection by typing C-i in the image window, the
background can be lightened by using the
perturbation method described
6.2.5 to adjust the Value channel
of the Curves tool. As shown in
6.42(b), the result produces a subject
Background Lightened with Curves: (a) Before and (b) After
is better defined against the background. This is compared with the
image from the previous step, which is shown again in
The final enhancement to the image is to sharpen the subject a bit.
This is done using the Unsharp Mask as described in
6.4.1. The Unsharp Mask parameters were
chosen to be 3 for Radius and 0.5 for Amount. The final
result is shown in Figure
Comparison of Original and Enhanced Photos
(a) shows the initial image from
. The comparison of the two images
is dramatic. The original seemed unretrievable, and, although the
final result is perhaps unworthy of National Geographic
magazine, it is, nevertheless, greatly improved.
The new image has several qualities worth noting. First, the colors
of the enhanced image are much sharper and better defined. In
comparison, the original image's colors are muddy. This is due
primarily to the enhancement to the tonal range. Second, the green
tinge seen in the original image has been eliminated; the subject of
the enhanced image is also sharper and better defined against the
background. This is due to the Unsharp Mask and the
reprocessing of the background with the help of selection tools and
the Curves tool.