Thursday, September 07, 2006

Digital Blending

My views on HDR and digital blending follow that of Michael Reichmann:

"In many ways, Photoshop CS2's HDR function is the holy grail of dynamic range. With properly shot and processed files it allows photographers to easily create images that were previously impossible, or at least very difficult to accomplish. But, good as it is, like a gun or nuclear power, it can be a force for evil as well as good."

In other words I'm not fond of the over done HDR photos that have clogged flickr explorer for the past few months. Just because you can over do HDR does not mean you should but if you must, I guess I can look the other way. Ok my rant is done and on to the point of this post.

This is a digital blend of two photos bracketted by 2-stops

I'm sure, like me, you have all taken pictures of a beautiful sunset or sunrise only to be disappointed with the results. Either the foreground shows detail and the sky is way over exposed, because of the setting sun, or the sky looks "right" but the foreground detail is lost in the darkness. With film or a "point and shoot" camera you are left to compromise between exposure settings (unless you are using a ND filter). However, with a digital camera that has some manual settings you have the ability to get photos, after some post processing, which are more like what your eyes see.

This was my first attempt
at digital blending, from a year ago, and is on the edge of being unnatural looking.

1/200 sec 1/2500 sec
Digital blending
Digital blend
The third picture is a digital blend of previous two different photos. With the camera on full manual I first set the following parameters: ISO 100, f/2.8, 70mm, and a shutter speed of 1/200 sec. With the low shutter speed the camera picks up the rocks in detail and the houses in the background but the sky, because of the sun setting, is way over exposed. The second settings were: ISO 100, f/2.8, 70mm, and shutter speed1/2500 sec. This results in a nice sky but a very dark foreground. Now, using the tutorial at on blending in photoshop I obtained the blended image on the bottom.

When I took these photos I used a tripod and a constant f stop so the depth of field would not change. Also, I used CR2 (canon raw 2) format instead of jpeg during the blending. The raw format is the uncompressed data captured by the camera and can make for some large files. If you digitally blend these photos using layers and masks as in the tutorial the file size grows again. I finished with about a 100 MB file if I saved it as a photoshop image (retains layer info), about 50 MB for uncompressed TIF, and 7 MB for JPEG.

The 20D has Auto Exposure Bracketing (AEB) which will change the shutter speed or aperture automatically as you shot three successive photos. In this fashion, the camera "brackets" the exposure up to +/- 2 stops in 1/3 increments. This can be handy but for large contrasts in lighting it may not give you a large enough dynamic range. You will notice that the shutter speeds of the two original photos are about 3.5 stops apart.

Here is a more recent digital blend:

Night worship


Blogger martin said...

damnit, when did you get a blog? :)

Good writeup on blending, my feelings on it lean more towards it being a great form of art, but not really photography. I like the results, but like you, it's annoying that the explore page is clogged with tons of them now...

10:28 AM  

Post a Comment

<< Home