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hand-blending high dynamic range (hdr) images using luminosity masks



Blending the Dark Tones

Believably increasing the brightness of the dark tones in the image turned out to be more of a challenge than recovering the light tones. Luminosity painting was again used, but required a bit more experimentation. Here's the way I ended up doing it.

First, turn off the top Underexposed layer by clicking off the eye in the box to the left of the image. The new masks that will be created to blend the dark tones will be affecting the Normal layer, so it's important to create the masks from this layer. Turning off the Underexposed layer means the actions will create the new masks using the tonal information from the Normal layer.

Next, make all the Darks-series masks on the Channels palette (Figure 13). Since blending is now concerned with rescuing the dark tones, one or more of the Dark-series masks will be needed.

Figure 13
Figure 13

Create a Reveal All layer mask on the Normal layer. Click the Add-layer-mask button at the bottom of the Layers palette (red circle Figure 14) to add a white layer mask to the Normal exposure layer. The newly created layer mask should be white this time, not black. (Don't Alt+click the Add-layer-mask button like last time or the mask will be black.) Alternatively, use the menu command Layer > Layer Mask > Reveal All to create the white layer mask. When finished, the Layers palette looks like Figure 14 (the new layer mask is outlined in yellow).

Figure 14
Figure 14

The proper mask for the painting operation this time turned out to be a combination of two masks from the Darks-series. I loaded the Darks as a selection—Ctrl+click (Mac: Cmd+click) on the Darks mask on the Channels palette—and then subtracted the Shadow Darks—Alt+Ctrl+click (Mac: Opt+Cmd+click) on the Shadow Darks mask. What resulted is one of those special offset mid-tones masks discussed in The Magic Mid-tones tutorial. One of the straight Darks-series masks will not work here because painting through it reveals too light of tones underneath and loss of depth in the shadows. I need to preserve the darkest values of the normal exposure, and subtracting the Shadow Darks from the Darks allows this to occur.

The mask of the Darks minus the Shadow Darks is shown in Figure 15. Looking at this mask it can be seen that the darkest textural details in the arch and surrounding rocks are also dark in the mask. This comes from subtracting off the Shadow darks when the mask was created. These dark details help retain the dark values of the Normal layer during the painting operation. Rolling over this image with the mouse will show a mask of just the Darks, no subtraction. As you can see, the darkest values are very light in the rollover mask and would over-reveal the light tones in the Overexposed layer underneath if just the Darks mask was painted through. So the subtraction of the Shadow Darks is essential to preserving the darkest textural details in the image. Don't forget to turn off the marching ants—Ctrl+H (Mac: Cmd+H) once the subtracted mask selection is created.

Figure 15
Figure 15

Before starting to paint on the mask on the Normal layer, turn the top, Underexposed layer back on by clicking the eye box next to the Underexposed image. This makes it possible to visually take into account the already blended light values in the sky while painting to restore the proper brightness in the dark tones.

Because painting is occurring on a layer that already appears too dark, the goal is to conceal some of the overly darker tones in the Normal exposure and allow the lighter tones from the Overexposed image to show through. Black paint is needed to conceal, so black is chosen as the foreground color (Figure 16).

Figure 16
Figure 16

Figure 17 shows how the final paint job for the layer mask looked. It's quite different than the subtracted mask that was painted through (Figure 15). For one thing, it’s a negative of the subtracted mask. That's because black was used for painting, which creates a negative image as it paints through the luminosity selection. Also, it's much blotchier in some areas where extra paint was applied to the layer mask. This was done to better hide the dark tones on the Normal layer and allow the lighter tones in the Overexposed layer to show through. So even though it looks quite different, luminosity painting through the subtracted mask once again allowed that mask to be highly customized for this particular image. The painted layer mask also clearly shows how the dark-textured elements from the Normal layer are still light in the finished mask. This means that they are still revealing the dark tones of Normal layer instead of the lighter tones in the Overexposed layer underneath—exactly what was desired.

Figure 17
Figure 17

Figure 18 shows what the Layers palette looks like after the two custom blending masks have been completed.

Figure 18
Figure 18

Figure 19 shows the blended image.

Figure 19
Figure 19

While it's not done yet, the histogram (Figure 20) is looking pretty good. From here it will be relatively easy to Photoshop the image to its final form.

Figure 20
Figure 20