Digital Blending

Understanding Digital Blending
Three Approaches to Expanded Dynamic Range
When Shooting With A Digital Camera
Thissubject is featured in Issue #6 ofTheLuminous Landscape Video Journal.
The Problem Being Solved
In nature when doing landscape work that includes sky, especially early orlate in the day, the contrast range encountered often exceeds that which filmor imaging chips can handle. It‘s therefore necessary to find a way to reducethe contrast range to something that the camera can handle so that the highlightsdon‘t burn out and the shadow areas don‘t turn inky black.

The Traditional Approach
The traditional method of dealing with this is to use split neutral densityfilters (graduated filters, some call them).
This works well much of the time, and I have rarely gone out shooting withoutmy full filter kit at the ready. 1 stop, 2 stop and 3 stop grads, and soft andhard edged versions of each. Add filter holders and adaptor rings and the wholekit can cost over a thousand dollars and fills a small shoulder bag.
An additional downside is that using them takes time. Deciding which gradientto use and what density, attaching the rings, holders and filters and then liningthem up. This takes several minutes, no matter how prepared and experiencedone is, and of course the times that the use of grad filters are needed areinvariably when the light is changing quickly.
Is there a better way? Yes, if you‘re shooting digitally.
The technique discussed below can be used if you‘reshooting film, but they require that the scans made be very precisely made andaligned, something that I won‘t be exploring in this particular tutorial.

Shooting Technique
What you‘re going to do is take at least two separate frames of the scene.One will be exposed for the highlights and one for the shadows. Usually therewill be a two to three stop spread between them.

(Dark Frame) Exposed for the Highlights
(Light Frame) Exposed for the Shadows
The simplest way to do this with a digital camera is to set the camera forauto-bracketing. Most cameras will take three frames in rapid succession — onenormal, one underexposed and one overexposed. Set your camera so that the darkand light frames are each about 1.5 stops apart from normal. (The middlenormally exposed frame is redundant, but it‘s worth having as back-up if yourblend doesn‘t look right).
My preference is to set the camera to Aperture Priority andeither manual focus or Single Shot focus. Tripod mountedis preferable as well. The reason for all this is that you don‘t want thereto be any difference between frames. If the aperture is varied there will bea focus and depth of field shift. If the focus varies the frames won‘t lineup, and if the camera moves you‘re completely out of luck. I have had successhand-holding such shots, but only of the lens isn‘t too long and the shutterspeed is high enough to ensure that during the 3 frame burst there is no movement.It‘s better to use a tripod.

Common First Steps
The following steps are common to all three approaches. Use your favouritedigital image retrieval program to convert the dark and light frames to 8 bitTIFFs. This technique will work on JPGs as well, but not on RAW files. If you‘veimported your files into Photoshop in 16 bit mode, reduce them to 8 bit. Update:You can work in 16 bit mode in Photoshop CS, but the combinedfile size will get very large.
Put both images onscreen at the same time. Select the dark frame and pressCTRL-A to select the whole thing. (Of course you‘ll alwaysuse Command instead of Control if you areusing a Mac.) Press CTRL-C to copy it. Close that picture,as you no longer need it.
Select the light frame and press CTRL-V to paste the darkframe into it.
Fig. 1
If you look at the Layers palette (Figure #1) you will now see your light imageas Background Layer and your pasted dark image as Layer1.
There are now three different approaches that you can try so as to blend theseimages together to increase apparent dynamic range. The first, what I call ThePainted Mask, is the traditional method that‘s been around a longtime. I still use it extensively when working with scanned film. It is the mostlabour intensive of the three and requires some manual dexterity on your part.It also is the most flexible.
The second, that I call The Layer Mask, is easier,and doesn‘t require any eye-hand coordination on your part, while the third,Fred Miranda‘s DRI Action, is the simplest of allto use, but you have to purchase it.

The Painted Mask
This is the most labour intensive of the manual methods.
Use Layer / Add Layer Mask / Hide All. Now select the PaintbrushTool and choose a fairly large brush. Start painting over the light part ofthe image. You are removing the overexposed layer and revealing the darker imageunderneath. Don‘t worry about overdoing it because once the light layer is removedthe process stops. Be careful not to get too close to the dark area with thelarge brush. Also, make sure that you don‘t miss any areas that you want toinclude.
Change to a smaller brush and increase the magnification. Very carefully erasethe light layer along the edge of where the dark area meets it. If you makea mistake, use the History Palette to go back.
The only drawback with this method is that it requires sometimes finiky painting,and this can become difficult if the dark and light areas aren‘t large and easilypaintable. The advantage is that it gives you very precise manual control ofwhat gets blended and what doesn‘t.

The Layer Mask
This is the easiest manual technique. Starting with having done the pastingof the dark image on the light one, add a Layer Mask. This is done by clickingon the second icon on the lower left of the Layers palette. You will now seea white rectangle next to the image on the Layer 1 layer. (See Figure#2).
Fig. 2
Click on the background layer on the palette and the press CTRL-A toselect the whole image. Press CTRL-C, copying it to the clipboard.Now hold down the ALT key (Option on the Mac) and click on the whitemask rectangle on the Layer 1 palette.
The whole image will now turn white. Next, press CTRL-V to paste the contentsof the clipboard onto the white mask. You will now see a B&W mask image.With the B&W mask displayed go to Filter / Blur / Gaussian Blurand set the Radius to about 40 pixels. Click on the Background Layer and you‘redone. (Thanks to George DeWolfe of CameraArt‘s magazine for bringing thistechnique to my attention.)
Oh yes. With this technique you may want to select the background layer andadd an appropriate curve to brighten up the dark area a bit prior to flatteningthe layers.

Miranda‘s Dynamic Range Increase (DRI) Action
This approach is almost completely automated. TheDRIAction can be downloaded from Fred Miranda‘s site at a cost of U.S. $8.50.It is compatible with Photoshop versions 5 through 7.
Fig. 3
Download the Action and following the provided directions load it into yourActions palette. With the two images overlayed, as detailedabove in Common First Steps, click on the DRI headingand press the Play arrow. You‘re done.
My recommendation though is that before using DRI you open your dark framein 16 bit mode and extract as much shadow detail as possible, because unlikewith the prior two techniques you can‘t work on just the shadow areas once theprocessing has been completed.

Next Steps

This is the final bended image. All three techniques produce roughly similarresults, with the painting technique providing the most control but also themost work. The Layer Mask technique is easy to use and costs nothing. Miranda‘sDRI Action costs a few dollars but is simplicity itself to use.
Once the image has been flattened your work has just begun. Now you can dofine tuning of Layers and Curves and colour balance, as well as any other adjustmentsthat you care to make. But, you‘ll be starting with an image that is much closerto what you‘ll likely want the final print to look like than if you had triedto coax detail from the shadows the traditional way. Of course blown-out highlightwould have been irretrievable. Naturally any sharpening should be saved forlast, preferably just before printing.
Incidentally, once I had blended the example above I found that there was quitea bit of flare in the frame from shooting almost directly into the setting sun.I‘ve still used this as an example because it illustrates some of the thingsthat you‘ll discover when you reach into previously unseen areas of your imageswith these kinds of techniques.

Additional Examples
Here are a couple of additional examples. These were each doneusing the simple and quick Layer Mask technique, and each wasaccomplished in about 30 seconds. I‘ve applied no corrections at all to anyof the files, though I could have easily added some Levels or Curvesadjustments to each as needed. I simply wanted to illustrate how fast andeasy this approach can be, and how if you‘re shooting with a digital camerathe use of split ND grad filters has essentially been rendered obsolete.



Be careful when using these techniques that you keep your prints natural looking.People expect the foreground to appear dark when the sky is bright — don‘t overdoit.



That‘s all there is to it. When you encounter a scene with very high contrastsimply set your camera to auto-bracketing and do a few frames about 2 to 3 stopsapart. You‘ll soon wonder how you ever did without this technique.