Ninguna, me gusta que sea simple
3. ANTECEDENTES Y ESTADO DE LA TÉCNICA
8.3 Proceso de corte láser
P
hil Bard shot the photo shown in Figure 18.1 in 1986 in Yosemite Valley, California. This image is the result of several contrast manipulations of the original scan, and is basically “finished” except for the fact that, to Phil, the foreground tree details lack sufficient brightness. He wanted it to stand out a little more from the darker background. Selecting the general area of the tree and performing a Levels or Curves adjustment would be one way to achieve this, but that would also lighten mid-tone areas of the background somewhat as well. Instead, he chose a more surgical approach, one that affects only the tree. In this technique, you discover how Phil was able to extractthe tree based on its value. In other words, a specific range of tones is selected based on their location in the histogram.The Photoshop 7 masking and adjustment layer features have many applications, one of the less obvious being the ability to extract image information with respect to value. This is a useful technique for mimicking a darkroom technique called bleaching, in which highlights are lightened without significant effect to the mid-tones and shadows.
TECHNIQUE
18
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Cottonwood on the Merced River in Spring Linhof Monorail camera mounted on a tripod, 210mm lens with yellow filter, Kodak PlusX, 10 seconds @ f/16, scanned (wet) on a ScanView drum scanner yielding 100MB file, down-sampled to 2400 x 1920 pixels, 4.4MB grayscale. tif
A B O U T T H E I M AG E
If you want to use this technique on RGB or CMYK images, you will need to select the channel or channels you want to load as the selection. In the case of the image used in this technique, the image is a grayscale image and there is only a single channel to load.
■ Click the Quick Mask Modebutton (Q) in the
Toolspalette, which will create a mask from the selection. Your image should now look like the one shown in Figure 18.3.
■ Hide the Gray channel by clicking the eye icon (to switch it off) in the Graylayer in the Channels
palette so that you can better view the mask. Notice that the mask is now thinest (lightest) over the highlight areas. Remember that you are look- ing at a black and white mask, not the black and white image.
To get an even clearer view of the mask’s gradation, increase the image to 100%by choosing View ➢
Chapter 3 Working in Black and White
STEP 1: OPEN FILE
■ Choose File ➢ Open(Ctrl+O) to display the
Opendialog box. Double-click the /18folder to open it and then click the cottonwood-before.tif
file to select it. Click Opento open the file.
STEP 2: SELECT LIGHTEST PARTS OF THE IMAGE BY VALUE
■ If the Channelspalette is not visible, choose
Window ➢ Channels. In the Channelspalette, click the Load Channel as Selectionbutton (the left-most button), located at the bottom of the
Channelspalette. This creates a graduated selec- tion of the entire image based on value, with the lightest details being most selected (least masked) and the darkest, least selected (most masked).
Actual Pixels(Ctrl+Alt+0). Choose View ➢ Fit on Screen(Ctrl+0) to fit the image on the screen.
STEP 3: REDUCE SELECTION TO JUST THE COTTONWOOD TREE
■ Because we want to further reduce the
selection so that we can make changes only to the Cottonwood tree, edit the mask further. Click the
Quick Maskchannel in the Channelspalette to select it if it is not already highlighted.
■ Choose Image ➢ Adjustments ➢ Curves
(Ctrl+M) to get the Curvesdialog box.
■ In the Curvesdialog box, drag the curve into the shape illustrated in Figure 18.4.
To make the Curvesdialog box show a 10 by 10 grid instead of a 4 by 4 grid, press Altwhile clicking inside the curve box.
Set the lower end-point so that the Inputand
Outputvalues are 50%and 0%respectively.
Isolating and Extracting Detail Using Values
Set the upper end-point so that the Inputand
Outputvalues are 75%and 100%respectively. Click OKto apply the settings.
This Curves adjustment increases the density of the mask in the highlight areas, while eliminating the shadow and some of the mid-tones, which helps to isolate the tree itself. This is a crucial adjustment that must be done to make this technique work.
■ Click the Lassotool to draw a selection around the Cottonwood tree on the left of the image as carefully as you can, excluding the water and rocks where possible. Absolute precision is not neces- sary, but make sure you include all of the tree branches.
■ Choose Select ➢ Inverse(Shift+Ctrl+I). Make sure that the background color is set to black. This is very important! Press the Deletekey. This eliminates the non-tree areas from the mask. Your image should now look similar to the one shown in Figure 18.5.
■ Choose Select ➢ Deselect(Ctrl+D) to remove the selection marquee.
■ Click the Erasertool (E) in the tool palette. In the Optionsbar, set Modeto Brush,Opacityto
100%, and Flowto 100%. Using the Erasertool, erase any of the detail you want, while leaving only the tree. This means that you should be erasing areas where there are large amounts of black. Be careful not to use too large a brush and erase important detail. To do this, you may want to vary the size of the Erasertool from 35pixels to 100
pixels by clicking the Brush Preset Pickeron the
Optionsbar.
■ Now we are ready to apply the mask. In the
Channelspalette, click the Graylayer and then click the Standard Modein the Toolspalette. Notice that a marquee appears indicating that the mask has now become a selection.
Click OKto apply the settings. This curve increases the contrast of the layer, which makes the Cottonwood tree stand out from the other trees, as shown in Figure 18.2.
If you uncheck and recheck the eye icon in the Curves 1 layer in the Layers palette, you can view the results of this new adjustment layer. Of importance is the fact that any changes made to this curve apply only to the tree, which has been extracted, so to speak. Remember that, because this is an adjustment layer, you can always go back and edit its effect. And because the mask you just made resides in this layer, you are able to load it as a selection and add more adjustment layers if you want.
This useful technique is applicable in many ways beyond what we have explored here. By inverting the color of the mask (during editing in Quick Mask mode), it can be used to select shadow areas and therefore increase or decrease their local contrast. Another approach you may want to try to get a simi- lar effect is to duplicate the background to a new layer, then set the blend mode of the new layer to a lightening mode and use the Blend If sliders. This would create the same results; however, it would not be limited to just a masked area.
To learn more about Phil Bard and his work read his profile at the end of Technique 16.
Chapter 3 Working in Black and White
■ Choose Layer ➢ New Adjustment Layer ➢ Curvesto get the New Layerdialog box. Click OK
to get the Curvesdialog box. Click the curve in the
Curvesdialog box to set a point at 34and 24.
Click the curve again to set a second point at 80
and 85. The Curvesdialog box should now look like the one shown in Figure 18.6.