Chapter Contents Recognizing Color Casts Removing Color Casts Adding a Color Cast Modifying Colors to Match Nature or Add Impact Using Layer Masks with Color Adjustments... Using Hue/Sat
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P hoto by J osh A non
Color Adjustments
Color often creates strong emotional reactions, drawing you into a photo or making you pass it by Expressive images with the most impact use color wisely to direct our attention and elicit reactions
Nature photographers have more choices
to make about the colors in their images than do most photographers Other types
of photographers must maintain neutral colors, but we nature photographers are often looking for color casts, such as the warm glow of early morning light Although we’re often trying to create as natural-looking an image as possible, we also have a great deal of latitude to modify colors to make our images more expressive.
Chapter Contents
Recognizing Color Casts Removing Color Casts Adding a Color Cast Modifying Colors to Match Nature or Add Impact Using Layer Masks with Color Adjustments
Trang 2Recognizing Color Casts
sometimes, despite the fact that you may have previously adjusted the white balance
in the raw converter, you may look at your image and decide that the colors just aren’t quite right You may or may not be able to identify which color is the culprit, but you know something is off At other times you may not even be aware there is a color cast until you do some checking there are several ways to detect a color cast
Using Hue/Saturation to Reveal a Color Cast
An easy way to identify a color cast is to open a temporary Hue/saturation adjustment layer—click the Adjustments panel icon , choose Hue/saturation , and drag the saturation slider all the way to +100 Although your picture will look weird, this will show you where there are colors that don’t belong think for a minute about what col-ors you’d expect to see versus what you do see, since the colcol-ors are supersaturated Pay attention to the hues, particularly in areas that should be mostly neutral (white to gray
to black) to determine whether there are unexpected colors appearing
choos-ing Layer > New Adjustment Layer—we recommend opening all adjustment layers from the Adjust-ments panel or from the icon at the bottom of the Layers panel That way, you won’t accidentally find yourself choosing Image > Adjustments on the main menu and working directly on your pixels
As an example, Figure 7.1 shows a picture of a snowy egret with no obvious color cast and the same image with the Hue/saturation slider pulled all the way to +100 Although you expect the water to turn blue or blue/cyan and the sand to turn yellowish, you do not expect the egret to be magenta Clearly there is at least a partial magenta cast to this image
Figure 7.1 At first glance, there is not an obvious color cast in this picture (left) Boosting the saturation to +100 reveals an
unexpected magenta cast in the snowy egret (right)
Trang 3note that early-morning outdoor pictures on what will be a sunny day often have a cyan cast to them Pictures taken in shade often have bluish casts magenta
casts are also common, particularly with landscape pictures or images that include a
partly cloudy sky
if pulling the Hue/saturation slider has revealed an obviously problematic color cast, it can be tempting to just go to the channel containing that color and reduce the
saturation occasionally that approach will work, but the problem is that it reduces
the saturation of that color throughout the entire image, even in areas that should be
that color there are several more useful approaches to removing the color cast, which
we will describe shortly
After using the Hue/saturation adjustment dialog box to identify a color cast, click the trash can icon to remove this layer You need it only temporarily to give you
an idea of whether you should consider doing something to remove a color cast
Using the Info Panel to Reveal a Color Cast
When we talk about “neutral” in a digital picture, we’re referring to the relationship
of the red, green, and blue (rgB) values for any tone, from pure white (where the
rgB values are 255,255,255) to pure black (rgB values 0,0,0), as well as all tonalities
of gray in between (in which the red, green, and blue values are all nearly identical)
neutral also means that pixels that should be pure red will have an rgB reading of
255,0,0; pure green will be 0,255,0; and pure blue will be 0,0,255 the farther away
from these readings any pixel is that should be neutral gray or pure red, green, or blue,
the more of a color cast there is We nature photographers rarely, if ever, need to be
concerned with total neutrality in fact, outdoor lighting almost always imparts a
color cast—sometimes warm, sometimes cool nonetheless, it’s important to
under-stand what neutral would be
understanding the values that neutral pixels should have enables you to check for a color cast by using the info panel to access it, choose Window > info if there
are any areas of the picture that you know should be neutral (pure white, gray, or
black), zoom in and place your cursor over that area take a look at the info panel to
see the rgB values of that point
if the pixel is neutral, the values should be all the same (or very close) if one value is higher than the others, there will be a cast in that direction For example, if
an area that should be neutral has roughly equal blue and green values but a higher
red value, the picture has a reddish cast Conversely, if the number for one channel
reads lower than the other two channels, the cast is toward the opposite color of that
channel table 7.1 lists all the ways that one rgB channel might differ from the other
two, thus creating a color cast
Table 7.1
If This Value Is Off… …This Cast Will Be Seen
Continues
Trang 4If This Value Is Off… …This Cast Will Be Seen Green high Green
Green low Magenta
Blue low Yellow
in Figure 7.2, a reading taken from the wing of the white pelican should be close to neutral instead, it shows markedly lower red values, reflecting a cyan cast throughout the image
Figure 7.2 You know this image has a cyan color cast because the RGB values of a sample from the white wing (point #1 in the Info
panel) are 139,152,150
magenta, and yellow) will make your color adjustments much easier and more predictable Red and cyan are opposites, and green and magenta are opposites, as are blue and yellow Once you appreciate this fact, you’ll know to add cyan to reduce a red cast, add green to reduce a magenta cast, add blue to reduce a yellow cast, and so on
if you have determined that there is a color cast in your image, you’ll have to decide whether to eliminate it not all color casts are bad! remember that part of the reason many nature photographers prefer early-morning and late-afternoon light is for
Table 7.1
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the lovely warm (yellow/red) quality it imparts to their subjects as opposed to the more
neutral or cooler light that may occur in the middle of the day
Removing Color Casts
there are a number of different approaches to removing color casts depending upon
the individual circumstances, one approach is likely to be preferable in a particular
situation, whereas another approach may be more effective in another For that
rea-son, we’ll present several ways to deal with color casts, some of which are objective
and some subjective
accu-rate as possible, take a shot with a gray card or other neutral gray object in the frame That way, you can use it as the source for the eyedropper and ensure accurate neutral color
Subjective Methods for Removing a Color Cast
First we’ll look at the subjective ways to remove a color cast from your image some of
these approaches allow Photoshop to do most of the work for you, while others offer
considerable individual control over the process and invite a great deal of personal
preference
Using the Gray Eyedropper
if there’s an area that you know should be neutral—it can be any tonality from almost
white to almost black and any shade of gray in between—there is a very simple way to
eliminate the color cast in your picture
1. Create a new levels adjustment layer by clicking the Adjustments panel icon
and selecting levels
2. take the time to double-click the word Levels in the layers panel and rename
the layer; we use the name “color cast.” that way, if you return to this file later, assuming you save it with your layers intact, you’ll know exactly what you did
in each layer
3. Click the gray (middle) eyedropper to select it, and then click the area of your
image that should be neutral Photoshop will automatically define the point you click as “neutral” (that is, having equal red, green, and blue values) and will remap the rest of the image accordingly
You can do the same thing using the gray (middle) eyedropper in the Curves Adjustment layer controls; the results will be just slightly different, since levels uses
a linear algorithm to do the remapping whereas Curves naturally uses a tone curve
Practically speaking, the results will be very similar in most cases the results are also
very similar to using the White Balance eyedropper in ACr