Thursday, February 16, 2006

Digital Secrets

The great thing about this blog is the interaction that it spawns. I enjoy hearing from each of you and feel like the dialog is easily as engaging as my posts. Sometimes a question is raised that starts a new conversation. My dad asked me about the technique I was discussing on Flickr that I used for the sunrise shot in the Hut Trip post. I figured the explanation merited a post of its own.

First, let’s start with the limitations of the sensor in a digital camera. For any given exposure a camera can only capture a fixed range of brightness or colors. This fixed range is smaller than the range that you can see with your eyes. So, if you try to photograph a scene that has a broad range of brightness, your picture will not look like what you saw. Since many of the pictures we take have color levels that fall within the camera’s range, this limitation often goes unnoticed. A picture that does not have both a bright light source and a dark shadow will generally be accurately captured. However, there are times when a scene has both a bright light source and dark shadows preventing the camera from representing both extremes in one image.

When a scene with a broad range of brightness is encountered, the camera has to choose whether it will capture the bright colors at the expense of the dark ones, or, capture the dark ones at the expense of the brights. A common scene with this issue is a sunrise. The range between the light area and dark area is much too wide for the camera to capture, so it usually chooses to properly expose the light area resulting in a nice pink sky with a black horizon. This silhouette is a pleasing image and makes a great picture; however, it does not accurately represent what the photographer saw. This dilemma describes the predicament I was in that morning at the hut.


The solution I chose was to take 2 images and then combine them on my computer. The first image was exposed for the foreground; note the detail of the snow on the branches. The sky in the first picture is completely blown-out and doesn’t have any of the red that I was looking at. In the second picture I exposed for the sky, capturing the rich, red colors that were present. In doing so I sacrificed the detail in the trees. Once I got home, I used Photoshop to combine the 2 images. I learned the process from a website called Luminous Landscapes in a tutorial they call Digital Blending. Check it out if you are interested in the actual detail of combining the images in Photoshop.

Traditionally, photographers would use a split neutral density filter to achieve this result. These filters block light at the top of the image while letting it through on the bottom allowing the photographer to pull off 2 separate exposures with one image.

Another technique worth mentioning is the use of fill-flash. Let’s say you have a colorful sky and you want to take a picture of someone in front of it. Without flash you will just get a silhouette of the person. But, if you turn on the flash you can achieve both the color from the sky and the person in the foreground.

Hope that helps, Dad. And, if anyone tries this out, I’d love to see your results.

9 Comments:

Blogger Carol said...

Very interesting, I will read those links and see if i can come up with something. Thanks for the explanation.

Thu Feb 16, 07:03:00 AM PST  
Blogger Johnny said...

Good explanation, even I could understand it. I guess that means we have to the photoshot program to try this out.

Thu Feb 16, 09:42:00 AM PST  
Blogger Jason Hill said...

You don't have to use Photoshop to achieve these results. I tried not to go into any specific Photoshop techniques in this article for that very reason. Many applications will allow you to take 2 images and stack them as layers. The only trick then is figuring out how to mask half of each image to get the blend you want.

Here is a list of free imaging apps.

Paint.net looks to have all the features you would need to do this.

If you give it a try and then run into a brick wall, let me know and I'll see if I can help.

Thu Feb 16, 09:59:00 AM PST  
Blogger Johnathan M. Thomas said...

you don't have to have PS but it sure is nice. Great tutorial.

If you look at my pic of the week, I tried putting the two together like you suggested. However, I wasn't has pleased with the results. I kept thinking, "give J a call so he can talk you through this." In the end I blended the two shots and felt pleased with the results.

But thanks to you, I have a new bookmark on my browser.

peace.

Thu Feb 16, 11:15:00 AM PST  
Blogger Jason Hill said...

Johno,
I have seen your image, as a matter of fact, I linked to it in this post as an example of a silhouette making for an excellent shot.

It looks to me like you don't need my help. Your combination of 2 images also illustrates another use for this digital blending technique--taking an interesting sky from one scene and combining it with an interesting foreground from another.

However, call me anyways I enjoy the collaboration.

Thu Feb 16, 12:52:00 PM PST  
Blogger Tim Lewis said...

Mmmm...Photoshop...

Thu Feb 16, 08:10:00 PM PST  
Anonymous Allan White said...

Jason, I love the composition. The snowy trees in the foreground (esp. at near left) add a wonderful sense of stillness (and cold!) to the scene.

I only have one minor critique. The foreground image and the background image have a color-temperature disparity. While you've captured the essence of the broad dynamic range the human eyes can see, doing so has made the mountains a bit too cold.

If the sunrise is the only light source in the image (which it is), the mountains would look a bit more pinkish-orange.

I also think that the dark image is a bit too dark - a stop or two lighter would make the scene look a little more natural.

Your original, lighter image looks a bit warmer. Did it get cooled off in the comp?

Awesome work! The matte must have taken a lot of time & effort.

Fri Feb 17, 10:28:00 PM PST  
Blogger kristi w said...

Here's a photography post from a local guy you might be interested in:
http://www.foldedspace.org/weblog/2006/02/rocky_mountain_school_of_photo.html

Tue Feb 21, 12:04:00 PM PST  
Blogger Steve Maxwell said...

I just want to learn to use my camera period. Can you offer me some tips with regular pointing and shooting. :-)

Wed Feb 22, 05:34:00 PM PST  

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