Photoshop cs5 cho nhiếp ảnh gia part 50 pps

308 c h a p t e r 8: COMPOSITES ■ Expanding Dynamic Range Until recently, the dynamic range, or exposure latitude, that we could capture in a single image was limited by camera and film technology. Often, especially during the midday hours, there was too much contrast to be able to capture in a single shot. We had to choose to give up detail in the highlights, the shadows, or both. Photo- shop enables us to combine several images of the same subject, taken using different exposures, to retain detail in the highlights and shadows while simultaneously having the midtones properly exposed. It’s almost magical how we can create an image that reflects what we actually saw, no longer limited by the exposure latitude of film. There are two approaches that we’ll describe to extend the exposure latitude in an image. One, that we call the “Cookbook” approach, is partially manual. The other takes full advantage of the completely revised and impressive HDR tool in CS5. Although you could simply stack two images, a light one and a darker version of the same image, and use a layer mask to reveal whichever layer is better exposed, it’s rare in nature photography to encounter situations where that will be the best approach. That works only if the areas that are exposed differentially have discrete boundaries that are easy to mask. It’s better to use one of the two approaches we describe here. First we offer some hints on how best to photograph a contrasty situation so that you can easily combine the shots in Photoshop. Shooting to Expand Latitude When you encounter a situation in which there is too much contrast to capture detail in the entire scene in a single shot, take several shots at different exposure levels to combine later in Photoshop, and keep these suggestions in mind: U• se a tripod, and take your first shot, exposing for the shadow areas. Check your in-camera histogram to ensure that the shadow areas do not spike against the left side of the histogram. If they do, take another shot, adding more light to the exposure. Don’t worry about the highlights; the overall image is expected to be too light in this shot. Note: If you don’t have a tripod, try setting your camera to auto-bracket three exposures, each at least one stop different. Set your camera so that you can hold the shutter down to take the three shots as quickly as possible, without having to release the shutter button between shots, if possible. T• ake a series of shots, varying the exposure by changing the shutter speed, not the aperture (which would change the depth of field). If you use aperture prior- ity, then you simply need to dial in different exposure compensation amounts for each shot. V• ary the exposures by one to two f/stops each. Don’t try to bracket by small increments such as 1/3 to 1/2 stops. When making an HDR composite, you don’t need small differences in exposures. 607343c08.indd 308 4/11/10 11:06:39 PM 309 ■ EXPANDING DYNAMIC RANGE C• heck the histogram to make sure that your darkest picture includes detail in the brightest part of the image; that is, there are no spikes on the right of the histogram and no flashing highlight warnings. Similarly, check to make sure that your lightest image (which has flashing highlights) has no spikes on the left side of the histogram. You want to make certain to capture detail in all the shadows. In some cases, you may need three, four, five, or more shots. D• on’t vary the lighting by using flash in one picture and not the next. Note: It’s not enough to simply expose for the midtones and bracket the shot by half a stop in both directions. Bracketing that way is usually insufficient to allow ample differences in the exposures to re-create as much detail as your eyes saw. Instead, make sure to check the histogram with each shot to ensure that the portion of the image you are exposing for falls within the bounds of the histogram, as discussed in Chapter 1, “Thinking Digitally.” The “Cookbook” Approach to Expanding Latitude Sometimes you need to combine just two exposures in order to create an image with detail in both the highlights and shadows. The “Cookbook” method has Photoshop do most of the tedious work of creating a very customized layer mask to use the best- exposed areas of each image to create the final composite for you in combining two images (see Figure 8.7). Figure 8.7 You can have Photoshop use the lighter image to create a mask to use while combining two dierent exposures. Take these steps to combine the two images: 1. Drag the dark image on top of the light image by using the Move tool while holding the Shift key. It’s important that the darker image goes on top. Note: For this approach to be successful, the images must align perfectly. After dragging the darker image on top of the lighter one, select both layers and choose Edit > Auto-Align Layers. 607343c08.indd 309 4/11/10 11:06:40 PM 310 c h a p t e r 8: COMPOSITES ■ 2. Add a layer mask to the dark image layer. 3. Make the background image active by clicking the background image layer, and press Ctrl+A/F+A to select the entire background image. 4. Press Ctrl+C/F+C to copy the image to the clipboard. 5. Highlight the dark image layer; hold down the Alt/Option key, and click the Layer Mask icon to make the mask appear where you usually see your image. It will be completely white at first. 6. Press Ctrl+V/F+V to paste the contents of the clipboard onto the white mask. Your layer mask should now appear to be a black-and-white version of the background layer, as shown in Figure 8.8. Figure 8.8 Hold down the Alt/Option key, click the Layer Mask icon, and then press Ctrl+V/F+V to make the mask appear in place of the image preview. 7. Alt/Option+click on the Layer Mask icon again to return to the normal image preview. 8. Apply a Gaussian blur (Filter > Blur > Gaussian Blur) with a radius between 0.5 and 80. Modifying the Gaussian blur is important to make the final result appear natural. The exact amount of blur needed can vary significantly accord- ing to the image. This is the step that people most often fail to do aggressively enough. In Figure 8.9 we used a blur of 71.6 pixels! Choose the amount of blur that results in the most pleasing blending of the two images. 9. Click the image icon on the darker layer, and press Ctrl+D/F+D to deselect. Your image should now reflect the best of both exposures (see Figure 8.11). 10. You may want to fine-tune the tonality of the image using a Curves adjustment layer if necessary or by further manually modifying the layer mask. 607343c08.indd 310 4/11/10 11:06:41 PM 311 ■ E X PA N D I N G DY N A M IC R A NG E Figure 8.9 By using the lighter image to create a mask for the darker image, Photoshop does most of the work to create a composite using the best of both exposures. 11. Create a Stamp Visible layer by clicking on the top layer, holding down the Alt/ Option key and going to Layer > Merge Visible, and continue with the regular workflow. For Photoshop Elements Users: The “Cookbook” Approach to Expanding Latitude 1. Drag the dark image on top of the light image by using the Move tool while holding the Shift key. It’s important that the darker image goes on top. 2. Select the Background layer and add a Levels adjustment layer by clicking the Create adjust- ments layer button and selecting Levels. Do not make any adjustments; simply click OK. 3. Group the top layer with the Levels adjustment layer, selecting the top layer and picking Layer > Group with Previous from the menu bar. 4. In the Background layer, select the entire image by choosing Select > All (Ctrl+A/F+A). 5. Choose Edit > Copy (Ctrl+C/F+C) to copy that layer. 6. Alt/Option+click on the layer mask for the Levels adjustment layer to make it active. The screen will switch to the layer mask and appear white. 7. Choose Edit > Paste (Ctrl+V/F+V) to paste into the layer mask. 8. Choose Filter > Blur > Gaussian Blur and apply a very small amount (1 pixel) of Gaussian blur to the layer mask. 9. Next we will adjust the contrast of the layer mask to affect the combined images’ con- trast. Add a Levels adjustment to the layer mask by selecting Enhance > Adjust Lighting > Levels with the layer mask still active. Continues For Photoshop Elements Users: The “Cookbook” Approach to Expanding Latitude 1. Drag the dark image on top of the light image by using the Move tool while holding the Shift key. It’s important that the darker image goes on top. 2. Select the Background layer and add a Levels adjustment layer by clicking the Create adjust - ments layer button and selecting Levels. Do not make any adjustments; simply click OK. 3. Group the top layer with the Levels adjustment layer, selecting the top layer and picking Layer > Group with Previous from the menu bar. 4. In the Background layer, select the entire image by choosing Select > All (Ctrl+A/ F +A). 5. Choose Edit > Copy (Ctrl+C/ F +C) to copy that layer. 6. Alt/Option+click on the layer mask for the Levels adjustment layer to make it active. The screen will switch to the layer mask and appear white. 7. Choose Edit > Paste (Ctrl+V/ F +V) to paste into the layer mask. 8. Choose Filter > Blur > Gaussian Blur and apply a very small amount (1 pixel) of Gaussian blur to the layer mask. 9. Next we will adjust the contrast of the layer mask to affect the combined images’ con - trast. Add a Levels adjustment to the layer mask by selecting Enhance > Adjust Lighting > Levels with the layer mask still active. Continues 607343c08.indd 311 4/11/10 11:06:41 PM 312 c h a p t e r 8: COMPOSITES ■ For Photoshop Elements Users: The “Cookbook” Approach to Expanding Latitude (Continued) 10. Drag the black and white points on the Output Levels slider until you have a moderate amount of contrast without clipping the white or black areas. The lower the contrast of this mask image, the higher the contrast of the combined image. The following image shows what the mask and Output Levels sliders might look like: 11. Perform a Stamp Visible by selecting the topmost layer and pressing Ctrl+Alt+Shift+E/ F+Option+Shift+E. 12. Set this layer’s blending type to Overlay and adjust its opacity until you achieve the results you want. The final set of layers will look similar to those shown here: 13. Fine-tune this layer further by creating Curves or Levels adjustments. If you have more images to blend, repeat these steps, going from the brightest image to the darkest image, until you have a final, combined image. If you used an adjustment layer in Step 13, make sure to select that adjustment layer and Stamp Visible (Ctrl+Alt+Shift+E/ or F+Option+Shift+E) before proceeding. 607343c08.indd 312 4/11/10 11:06:42 PM 313 ■ EXPANDING DYNAMIC RANGE Try It! Open the images called CanyonDark and CanyonLight from www.sybex.com/go /photoshopnature and try combining them using the “cookbook” approach. Expanding Latitude via Merge to HDR Pro Photoshop CS5 dramatically overhauled and improved the Merge to HDR feature. Merge to HDR Pro is a tool to combine multiple exposures (ideally three to seven exposures of the identical subject, although technically you can use it with two images) into one 32-bit image. Using 32-bit enables the image to have a greatly expanded dynamic range so that the final image can contain detail in shadow areas and in highlights that normally cannot be present in a single image. In fact, 32-bit offers more latitude than what you can even see on your monitor. However, the 32-bit image can be immediately converted to 16-bit or even 8-bit. Merge to HDR Pro creates an image containing the maximum amount of detail and color information possible, with very little work on your part. It ensures that the transitions among the exposures are gradual, with no harsh obvious edges. It sounds too good to be true, doesn’t it? In earlier versions, nature photographers were likely to experience several dif- ficulties using this tool. If anything changed between exposures—a tree branch blow- ing slightly in the wind, a leaf, anything moving—Merge to HDR often failed to give a good final image. Similarly, if there was any camera movement, it also didn’t work. In CS5 the Auto-Align algorithms have been tremendously improved. In addition, you can add a layer mask to an image to hide part of an image to help with objects that move. Although there is still no option in this version of the tool to allow you to manually align the images, it works far better than earlier versions. Situations with high contrast and static subjects are best for creating HDR composites. If a scene lends itself to using Merge to HDR Pro, follow the same steps we described earlier for taking shots to expand exposure latitude. After you have downloaded your images to your computer, access Merge to HDR Pro through Bridge directly or through Photoshop using these steps: 1. To select the files to use in Photoshop, choose File > Automate > Merge to HDR. The Merge to HDR dialog box (see Figure 8.10) appears. Click Browse to select the desired images, and then click Open, or if you have already opened the images, simply select Add Open Files. 2. Check the Attempt to Automatically Align Source Images box. 3. To select the images to use directly from Bridge, simply highlight the desired images, and choose Tools > Photoshop > Merge to HDR Pro. If you have opted to have Bridge auto-stack your HDR images, it will be even easier to choose the right files. Just be certain to select all images in the stack, not just the top image. 607343c08.indd 313 4/11/10 11:06:42 PM . CanyonLight from www.sybex.com/go /photoshopnature and try combining them using the “cookbook” approach. Expanding Latitude via Merge to HDR Pro Photoshop CS5 dramatically overhauled and improved. access Merge to HDR Pro through Bridge directly or through Photoshop using these steps: 1. To select the files to use in Photoshop, choose File > Automate > Merge to HDR. The Merge to. the desired images, and choose Tools > Photoshop > Merge to HDR Pro. If you have opted to have Bridge auto-stack your HDR images, it will be even easier to choose the right files. Just