Intro

It’s been a while since I posted an in depth technique article, so I thought I’d do another one.  Warning: Major photo geek out ahead.  If you’re not into HDR, panoramas, post processing, etc. please move along.

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OK, now that it’s just us photo nerds left, wanna see some sausage made?  Let’s get started.

My question to you:  What if you want more pixels in your final image, more dynamic range in both highlights and shadows, and better depth of field, all by using a much simpler technique than you might normally use?  How would you go about it?  I’ll explain one approach I used recently to make this lead photo from my previous post:

Finished image (click to view on Flickr)

I made this with a 12 megapixel Nikon D700, but my final image file is 4238 pixels wide by 5776 pixels tall (about 24.5 Megapixels).  It has good depth of field with objects from very close out to the horizon in focus.  It also has good dynamic range with both the ground and the sunrise & clouds well exposed.

Details

If you were going to create an image like this using conventional techniques, it could require 6 or more exposures.  You’d mount your camera on a tripod and manual focus. You might analyze the scene to decide on an optimum exposure.  Then you’d make three bracketed exposures around that, first of the lower portion of the image, then shifting your camera viewpoint up toward the clouds – three more bracketed exposures.  Then you’d use panorama software to combine the three pairs of images at each exposure value, followed by HDR software to combine the three resulting panoramas into an HDR file and tone map it.  You might have to play with the result quite a bit to eliminate noise, ghosting, etc. introduced by the HDR software.  And if you wanted to stretch the depth of field, you might go through this twice with different focus points, and combine them too.  In some situations, you could also try using graduated neutral density filters to control dynamic range.

Whew – that could be a whole lot of work!  I didn’t do all that.  Instead, I used a much simpler idea.  Basically, I just combined two images manually in Photoshop.

If you’re still with me, read on (it might look complicated, but it’s actually harder to read about than do).  Here are the details.

1. I hand held my camera and used an image stabilized lens so I didn’t have to worry too much about longer exposures.  The camera was in landscape orientation.  I used aperture priority, with matrix metering auto exposure, and auto focus using the center focus point.  When I made these, I held my camera very carefully to make sure there was no side to side movement and that the horizon was level so there was no rotation between shots, and I made sure there was at least 30% vertical overlap between the two images.  I also shot in RAW mode for the best dynamic range and control over processing.
2. For this first photo, I pointed at the sky and let the camera auto expose for the bright clouds and sunrise.  It also auto focused on the clouds in the middle of the frame.  It’s at 16 mm, ISO 200, and f/8 @ 1/160 sec.  Here’s the unprocessed RAW source image for the sky:



3. For this second photo I pointed down at the ground and this time the camera exposed for the dark foreground.  It auto focused on the ripples in the water just short of the first coot  (again in the middle of the frame).  It’s at 16 mm, ISO 200, and f/8 @ 1/25 sec. (almost 3  stops more exposure).  Here’s the unprocessed RAW source image for the ground:



4. Then I processed the RAW photos.  I used Capture NX2 and converted them to TIF, but you could use Photoshop to convert them and not need CaptureNX2.  I set picture control to neutral, white balance to daylight, enabled distortion correction, and tried to bring both photos closer in overall brightness.  Here are the two processed images:





5. Next I loaded the files into Photoshop as separate layers in the same file, and used Photoshop’s Edit / Auto Align Layers function to place the two images relative to each other.
6. At this point, I added a layer mask (reveal all) for the sky image and then painted black to remove the portions below the horizon that I didn’t need.  It was fairly easy to blend the images by changing the brush opacity and either erasing or painting in until it looked correct.
7. The final steps then are the same ones used for any photo:  crop, sharpen, levels, apply any creative filters you like, etc.

Once you go through this a few times, it’ll be easier and you can, of course vary some of these steps based on your own preferences.

Conclusions

I think this “Two Image Pano / HDR / Focus Stacking” technique can be really useful and it has several advantages over standard approaches normally used for this kind of image.

Benefits

• It’s simpler than conventional techniques, and yields very good results.
• You can hand hold in many cases, especially if you use an image stabilized camera or lens.
• It uses the camera’s auto exposure effectively to expose correctly for the different areas of the image.
• You can post process with just Photoshop – other software isn’t required.
• It greatly increases the dynamic range of the final image without requiring HDR processing or software.  It doesn’t require a straight line horizon like graduated neutral density filters would.
• Depth of field can be increased over that in a single exposure or in a conventional pano / HDR approach.
• It also substantially increases vertical field of view.

Limitations

This technique is situation dependent: It’ll only produce portrait or perhaps square orientation output images (although you’ll have lots of pixels to crop to other formats).  It only works where the scene is easily divided into two portions where the brightness varies vertically.  Also,the dynamic range increase available from just two images may not be enough in all situations.

So, should you use it?

Why not?  Under the right conditions, it can generate very good results with minimal effort.  Now that you’ve heard about this technique, you can watch for scenes where you may be able to use it.

Then you can try it – and please let me know how it works for you.

© 2011, Ed Rosack. All rights reserved.