Photoshop cs5 cho nhiếp ảnh gia part 46 docx

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 sim

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

Note: If while you are shooting you know that you will want to make sure the colors are as 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

and selecting levels

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

brightest and darkest values selecting the Highlights or shadows option instead allows you to primarily adjust the most extreme tonalities in your image You may want to adjust each of them slightly differently

this can be quite useful in some situations common to nature photography For example, if you have a white bird photographed in early-morning light on water, you may want to emphasize the warm light on the bird but not make the water appear too discolored to do this, click Highlights and adjust the sliders to allow for more yellow and red and possibly magenta than in the midtones and shadows, where you might be attempting to limit the color cast, as shown in Figure 7.4

setting the best position for the sliders can be challenging and is a subjective, visual decision if there is a strong color cast in your image, it’s often easiest to begin

by working with the corresponding slider in the midtones For example, if your image has a strong cyan cast, start by adjusting the Cyan/red slider for midtones then, if necessary, adjust the other sliders for midtone values; after that, click Highlights and adjust, and then click shadows to set those sliders You may be happy with the color balance after adjusting only the midtone sliders since they affect the majority of the pixels within most pictures

on the other hand, you may find it necessary to adjust each slider several times, and you may even discover that you can’t decide which setting you like best if you find yourself in that position, we offer two suggestions:

P

start again You might even pull it all the way to the right, then reset it and note the setting, and then pull it all the way to the left and readjust it to where it looks best Hopefully you’ll be able to find a position that looks good to you i

a couple of minutes When you come back, note your gut-level reaction to the picture Are the colors good, or are they too much toward a specific color cast? trust your immediate reaction, don’t overthink it, and then make any necessary changes

Tr y It! Open Colorcast1 from www.sybex.com/go/photoshopnature, or open an image of your own that you suspect has a color cast but includes an area you think should be neutral First deter-mine whether there is in fact a color cast (either use the Hue/Saturation slider method or check the Info panel) Next create a Levels adjustment layer, and click the middle eyedropper on a pixel that should

be neutral to remove the cast Turn off the visibility of the Levels layer (by clicking the eyeball next to

it in the Layers panel) Add a Curves adjustment layer, and click the same point with the Curves middle eyedropper Then alternate viewing the Curves and Levels layers’ visibility to compare the results

For Photoshop Elements Users: Removing Color Casts

Elements does not have a Curves adjustment layer, and the Color Curves tool is not suitable for removing color casts However, Elements does have a specific Remove Color Cast tool To access

it, select Enhance > Adjust Color > Remove Color Cast Then click on part of the image that should

be black, gray, or white, and Elements will remove the color cast This is similar to choosing Levels and using the gray eyedropper

Using a Color Balance Adjustment Layer

color casts in essence, it presents the sliders from each of the individual color channels within levels in one interface, along with the ability to set the sliders to affect primar-ily the midtones, shadows, and/or highlights As you pull the sliders, you are shifting the color values in your image toward the basic colors (red, green, and blue) or toward their opposites (cyan, magenta, and yellow), as shown in Figure 7.3

Figure 7.3 Color Balance provides an easy

interface to adjust the balance within each color channel as well as to make those changes

to the midtones, highlights, and/or shadows

tone is set by default to affect the midtones when you first open a Color Bal-ance adjustment layer When midtones is checked, the changes you make on the sliders affect the majority of the pixels and tones in your image, excluding only the

For Photoshop Elements Users: Removing Color Casts

Elements does not have a Curves adjustment layer, and the Color Curves tool is not suitable for removing color casts However, Elements does have a specific Remove Color Cast tool To access

be black, gray, or white, and Elements will remove the color cast This is similar to choosing Levels and using the gray eyedropper

brightest and darkest values selecting the Highlights or shadows option instead

allows you to primarily adjust the most extreme tonalities in your image You may

want to adjust each of them slightly differently

this can be quite useful in some situations common to nature photography For example, if you have a white bird photographed in early-morning light on water, you

may want to emphasize the warm light on the bird but not make the water appear too

discolored to do this, click Highlights and adjust the sliders to allow for more yellow

and red and possibly magenta than in the midtones and shadows, where you might be

attempting to limit the color cast, as shown in Figure 7.4

Figure 7.4 Adjusting the Color Balance sliders differently for the highlights than for the midtones enables you to leave more of a

color cast on the white bird while limiting the color cast on the water

setting the best position for the sliders can be challenging and is a subjective, visual decision if there is a strong color cast in your image, it’s often easiest to begin

by working with the corresponding slider in the midtones For example, if your image

has a strong cyan cast, start by adjusting the Cyan/red slider for midtones then, if

necessary, adjust the other sliders for midtone values; after that, click Highlights and

adjust, and then click shadows to set those sliders You may be happy with the color

balance after adjusting only the midtone sliders since they affect the majority of the

pixels within most pictures

on the other hand, you may find it necessary to adjust each slider several times, and you may even discover that you can’t decide which setting you like best if you

find yourself in that position, we offer two suggestions:

P

start again You might even pull it all the way to the right, then reset it and note the setting, and then pull it all the way to the left and readjust it to where it looks best Hopefully you’ll be able to find a position that looks good to you

i

a couple of minutes When you come back, note your gut-level reaction to the picture Are the colors good, or are they too much toward a specific color cast?

trust your immediate reaction, don’t overthink it, and then make any necessary changes

Objective Method for Removing a Color Cast

At times, even nature photographers want to make their images as neutral as possible, and in such cases an objective approach may be best We’ve also encountered some photographers who are color-blind and who don’t have the luxury of having someone close by to comment on the colors within their images sometimes they feel safest using an objective method to correct color casts

to objectively remove a color cast, you use all three eyedroppers in a levels adjustment initially you’ll identify and set the white and black points, and then you’ll have Photoshop define them as neutral

As you already know, you can hold down the Alt/option key while pulling the endpoint sliders within levels to identify the lightest and darkest pixels within your image However, you don’t want to have to rely on your memories as to exactly where they’re located instead, we’ll show you how to mark them to be sure you’re accurately targeting the darkest and lightest pixels within your image

to objectively remove a color cast, follow these steps:

the eyedropper tool (see Figure 7.5) make certain to set the sample size option

on the options bar to 3 × 3 Average rather than to its default value, which is a one-point sample the 3 × 3 Average option causes Photoshop to read an aver-age of 9 pixels, which prevents you from accidentally selecting a pixel that is different from its neighboring pixels

Figure 7.5 The Color Sampler tool allows you to mark particular pixels within the image (left) It’s best to set the

Adjust-ments panel

with no tones in between (see Figure 7.6) move the slider all the way to the right until the image preview becomes totally black

4. slowly move the slider to the left, and stop when you see the first pixels begin

to turn white these are the lightest pixels in your image

vital here

lightest pixels in your image, and click the tool leaves a small circle with the number 1 on your image (Alternatively, you can hold down the shift key and use the eyedropper tool.)

Figure 7.6 Your image will appear in black and white, with no in-between tonalities.

magnifi-cation control in the main menu bar

white gradually move it to the right, and note where the first black pixels appear these are the darkest pixels in the image

10. Place your cursor over one of the darkest pixels, and click this time, the Color sampler tool leaves a small circle with the number 2

icon in the Adjustments panel to remove it the selected pixels remain marked, and you have an objective indicator of the darkest and lightest pixels within your image, as shown in Figure 7.7

using this one to remove a color cast

want Photoshop to use if you have previously saved default values for black and white, you can skip this step:

type values of r = 10, g = 10, and B = 10 for the black point, and click

oK (if you have established a different set of black values for your printer, use them here.) Photoshop asks whether you want to set these as your default values Click oK

reap-pears type values of r = 248, g = 248, B = 248, as shown in Figure 7.8,

for the white point, and click oK Photoshop asks whether you want to set

Objective Method for Removing a Color Cast

At times, even nature photographers want to make their images as neutral as possible,

and in such cases an objective approach may be best We’ve also encountered some

photographers who are color-blind and who don’t have the luxury of having someone

close by to comment on the colors within their images sometimes they feel safest

using an objective method to correct color casts

to objectively remove a color cast, you use all three eyedroppers in a levels

adjustment initially you’ll identify and set the white and black points, and then you’ll

have Photoshop define them as neutral

As you already know, you can hold down the Alt/option key while pulling the

endpoint sliders within levels to identify the lightest and darkest pixels within your

image However, you don’t want to have to rely on your memories as to exactly where

they’re located instead, we’ll show you how to mark them to be sure you’re accurately

targeting the darkest and lightest pixels within your image

to objectively remove a color cast, follow these steps:

the eyedropper tool (see Figure 7.5) make certain to set the sample size option

on the options bar to 3 × 3 Average rather than to its default value, which is a

one-point sample the 3 × 3 Average option causes Photoshop to read an

aver-age of 9 pixels, which prevents you from accidentally selecting a pixel that is

different from its neighboring pixels

Figure 7.5 The Color Sampler tool allows you to mark particular pixels within the image (left) It’s best to set the

Adjust-ments panel

with no tones in between (see Figure 7.6) move the slider all the way to the

right until the image preview becomes totally black

4. slowly move the slider to the left, and stop when you see the first pixels begin

to turn white these are the lightest pixels in your image

vital here

lightest pixels in your image, and click the tool leaves a small circle with the

number 1 on your image (Alternatively, you can hold down the shift key and

use the eyedropper tool.)

Figure 7.7 The darkest pixel (bottom edge) and lightest pixel (corner of the mouth) in your image are

marked with a numbered target so you can easily identify them (Note the red circles are here for illustrative purposes only; you won’t see them on your image.)

Figure 7.8 By typing values into the Color

Picker, you can set the black and white values within your image and then save them as the default values for Photoshop to use in the future

Note: Because most of our printers can’t print in ways that allow us to differentiate shades of black all the way to 0,0,0 or whites all the way to 255,255,255, we have to use slightly different values Once those are set, we can save them as default values The actual ideal values for your printer may vary and can be determined by printing out test strips of blacks and whites at various values—(8,8,8), (12,12,12), (15,15,15), and so on—to determine where you can begin to see differences in the dark tones You can do

a similar test strip for the whites The values suggested in Step 14 work for many people

Carefully and accurately align the cursor with the point or the Color sampler tool marked with the number 1 When you have precisely aligned the cursor and the sampled point, left-click this remaps that point to an rgB value of 248,248,248, or neutral white verify this by looking at the info panel, which shows you the “before” and “after” values of the targeted points

cast within the image is neutralized (see Figure 7.9) in some images, however, you also need to use the gray (middle) eyedropper and click somewhere in the image that should be neutral

sam-pler tool, and hold down the Alt/option key As you approach a circle, your cursor changes to a scissors When you click, the circle is removed Alternately, simply hide them by choosing view > extras from the menu this toggles the visibility of the color samples simply hiding them can be a time-saver if there is any possibility that you might want to modify your color-cast adjustments

Tr y It! Open the image named Colorcast3 on the website www.sybex.com/go/photoshop-nature, or open one of your own images, and try removing the color cast using the objective method

You can compare the results with what you obtain using your favorite subjective method

this approach may seem quite long, but actually it’s pretty straightforward and a good way to set your black and white points as well as to remove a color cast objectively You could also use the eyedroppers in a Curves adjustment layer to achieve similar results You would follow the exact same procedure described in this section from within the Curves dialog box

For Photoshop Elements Users: Objective Method for Removing a Color Cast

Elements does not allow you to mark points on an image, so to objectively neutralize a color cast use the Enhance > Auto Color Correction

Adding a Color Cast

the reality is that nature photographers get up ridiculously early in the morning and

stay out photographing until the sunset is completely over because we like our pictures

to have the warm, special light of early and late day We tend to prefer the color casts imparted by this light because our photos have a different feeling in them and often create more impact on the viewer than more neutral versions of the same subject it’s possible to create color casts to simulate that light using the same subjective tech-niques we used before to remove color casts

For example, if you’re using the middle (gray) eyedropper from within levels or Curves and you click an area that should not be neutral, Photoshop will still be oblig-ing and redefine the values of that point to be neutral anyway, and the rest of the image then has a color cast this can be a good thing! You can introduce a slight warmth to your images this way by clicking a point that actually should be slightly bluish or cyan-ish, as shown in Figure 7.10 Conversely, you can make them appear cooler by clicking

a pixel that should actually be slightly yellowish or reddish remember that Ctrl+z/

F+z undoes your last step, so you can use a trial-and-error approach in finding the right spot to use obviously, this is a subjective way to determine the color balance within your picture that relies on Photoshop to do most of the work for you

For Photoshop Elements Users: Objective Method for Removing a Color Cast

Elements does not allow you to mark points on an image, so to objectively neutralize a color