Blended Exposures – Tutorial

Blending exposures is a technique to allow you to effectively increase the brightness range (dynamic range) in a photograph beyond what the film or sensor can capture normally.  You might be thinking, ‘well isn’t that what HDR is supposed to do?’  And you’d be right.  Some people don’t like HDR.  Some people don’t find HDR software overly easy to use or can’t get the tonemapping done the way they want.  Sometimes you don’t need 5 or 7 or 9 exposures to get the result you want.  The technique of blending exposures has been practised for many years and is still a useful tool to have in the toolbox.

To do this, you need at least two exposures of a photo at different exposure settings.  One properly exposed for the highlights, with dark shadows and one properly exposed for the shadows with overly bright highlights.  It’s best if the middle values in the different images you use are close to the same  The middle values may be a bit dark on the highlight shot and a bit bright on the shadow shot but still fairly close.

Below are the two exposures we’re going to start with.  Highlights on the left and shadows on the right.

Origina Images (click for larger version)

As with the other techniques discussed on this site, starting with the highest quality digital files is your best option.  Shooting RAW and converting those RAW files to 16 bit TIFFs will give you the most flexibility in the digital darkroom.  In the case of the shadows image with the overexposed sky, I pushed the Recovery slider in ACR all the way to the right in order to reduce the contrast and reduce the brightness of the sky, but it was still too bright to use on its own.

With the two images open, copy one onto the other (Select>All, Edit>Copy, Edit>Paste or CTRL+A, CTRL+C, CTRL+V).  It really shouldn’t matter which layer gets copied onto the other but in this case, I found I was able to get a smoother blend by using the shadows layer as the Background and copying the highlights layer on top of it.

With the layers stacked, double click on the top layer which will bring up the Layer Blending dialogue box.  The screen capture below shows the box open.  The layer blending sliders are highlighted.  This is what we’ll sue to blend the two layers together.

Layer Blend Sliders (click for larger version)

The layer blending sliders blend two layers based on the brightness values of each layer.  The black slider on the left controls the shadows or darker values, the white slider on the right controls the highlights or lighter values.  Values between the sliders are blended and values to the left of the black slider and to the right of the white slider are ignored.  If you hold the ALT key and click on the slider, it will split apart and you can move each half separately.  This feathers the blending of the values.  The screen shot below shows how I’ve adjusted the sliders to blend these two images.

Layer Blending Sliders (click for larger version)

The screen capture below shows how the highlight layer has been blended.  None of the foreground has been used and just a small portion of the sky to counteract the brightness.

Highlights (click for larger version)

With the two layers blended together, you can set about to make any necessary additional adjustments for the final look you want.  In this case, I added a Hue/Saturation adjustment layer to remove the blue colour cast from the foreground, a Curves adjustment layer to tweak the overall contrast, a Curves adjustment layer to just the foreground area, a small bump to saturation and brightness of the light at the top of the tower and finally a High Pass filter layer for sharpening.  You could finish off with some cloning/healing to remove the power lines and other distractions if you wanted.

Blended Result (click for larger version)

A similar result can be achieved using Layer Masks.  To use Layer Masks, you’d set the top layer as the mask and set it to Hide All or Reveal all depending on which shot you placed on top.  With a soft brush at a low Opacity and the proper foreground colour selected, you’ll go back in and paint the areas where you want the mask affected.  The screen capture below shows the effect of the Layer Mask and the portion of the mask that’s been painted in.  In this case, I placed the shadow layer on top and set my mask to Hide All.  With a white foreground colour, I selected a small, soft brush with an Opacity of 20% and gradually painted back in the areas I wanted the mask applied.

Layer Masks (click for larger version)

With the layers now effectively blended, you can make any additional adjustments to each layer or to both layers just as you would if you’d used the Layer Blending dialogue box to blend the exposures.



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