How a digital camera sensor works

WWW.cambridgeincolor.com has some of the best articles I have read that clearly explain the science and the techniques of creating digital images. Topics cover everything from light striking your camera's sensor to the perception of the final image by your eyes and brain. While technical in nature, the tutorials include excellent images and diagrams that clearly illustrate complex topics. An in depth understanding of how your camera works is certainly not a requirement for making great photos, but the more you know, the better chance you have of nailing that difficult shot or to bring out the best of each image in post-processing.

The following is a brief excerpt from the fist article in the tutorial section on how a digital camera sensor works:

A digital camera uses a sensor array of millions of tiny pixels in order to produce the final image. When you press your camera's shutter button and the exposure begins, each of these pixels has a "photosite" which is uncovered to collect and store photons in a cavity. Once the exposure finishes, the camera closes each of these photosites, and then tries to assess how many photons fell into each. The relative quantity of photons in each cavity are then sorted into various intensity levels, whose precision is determined by bit depth (0 - 255 for an 8-bit image).



Each cavity is unable to distinguish how much of each color has fallen in, so the above illustration would only be able to create grayscale images. To capture color images, each cavity has to have a filter placed over it which only allows penetration of a particular color of light. Virtually all current digital cameras can only capture one of the three primary colors in each cavity, and so they discard roughly 2/3 of the incoming light. As a result, the camera has to approximate the other two primary colors in order to have information about all three colors at every pixel. The most common type of color filter array is called a "Bayer array," shown below.



A Bayer array consists of alternating rows of red-green and green-blue filters. Notice how the Bayer array contains twice as many green as red or blue sensors. Each primary color does not receive an equal fraction of the total area because the human eye is more sensitive to green light than both red and blue light. Redundancy with green pixels produces an image which appears less noisy and has finer detail than could be accomplished if each color were treated equally. This also explains why noise in the green channel is much less than for the other two primary colors (see "Understanding Image Noise" for an example).

Leaving Space Behind Moving Subjects - Composition

While generally an interesting site, I find the daily emails from Digital Photography School to be somewhat hit and miss. However, this succinct article provides some great photographic examples of when it's appropriate to break some of the established rules of composition.

When photographing a moving subject the generally acceptable compositional rule is to place the subject in the frame with space in front of it to give it room to move into (creating ‘active space‘).

This is said to give the image more balance and provides the viewer of the image an answer to the question ‘where is the subject going?’

However rules are meant to be broken and as with every rule there are times when it can be very effective to break this one also.

New Lensbaby

Alli gave me my favorite Christmas gift this year - a Lensbaby 2.0

This simple lens allows for cool and creative blur effects. It’s basically just a couple of lens elements attached to plastic bellows. There a no electronics or even mechanical parts to the lens; even the aperture is set with a drop-in ring. You set the camera in manual mode, make your best guess on shutter speed (and ISO) based on the inserted aperture ring and then adjust to get best exposure (using the camera’s histogram display is helpful here).

The real fun and challenge is in focusing. This is accomplished by pushing or pulling the ring attached to the front element of the lens with your fingers. There is a ‘sweet-spot’ to the focus which can shifted to various areas of the frame by moving the front element slightly up or down or right to left. Everything outside the sweet-spot becomes progressively blurry. By angling the front element, you can produce some wild blur effects at the far edges and create a focal plane that is not parallel to the camera’s sensor.

It’s little quirky and tricky to get the hang of, but a whole lot of fun and it creates really cool images when you get the focus right. In a couple instances, it produced a weird blur in the center of the focus area that I really can’t account for. Nailing the focus definitely takes some practice. For me, the manual’s recommendation of focusing using the middle fingers on each hand felt a bit unnatural, but as I get used it, I’m finding it gives a greater level of control.



Overall, it’s neat gadget to have. It’s small, simple and light weight, so I plan to carry it regularly. However, I don’t want to over-rely on it as it can be a bit gimmicky. Check out my Lensbaby album for some example shots.

2008 Photography Resolutions

This blog is the result of one of my new years resolutions – to become a better photographer. I hope other people find what I am learning and documenting here useful in their own photographic pursuits; however, I’ll admit this blog is primarily for me. In writing down what I’m learning, I focus my thoughts and retain more.

To get to the point, here are:

Rob’s photo resolutions for 2008:

1. Shoot more
2. Produce more
3. Study more
4. Develop a workflow
5. Sell some photos

Shoot More
The only real way to get good at anything is to practice. I will take my camera more places and take more photos.

Produce More
Too many of my photos just sit on my computer. I plan to print more photos, share photos online and create more slideshows and albums. Hopefully, by the end of the year, I’ll have a decent portfolio to show for my efforts.

Study More
I’m actually off to a pretty good start on this one. I’m currently reading three photography books: Digital Photography Expert Techniques, Light: Science and Magic: An Introduction to Photographic Lighting, and Photoshop Artistry: For Photographers Using Photoshop CS2 and Beyond (Voices That Matter). In addition I just enrolled in a class on Photoshop for Photographers at SCAD Atlanta. I’ll be updating the site with tips and items I learn from all these sources.

Develop a workflow
This is one of the most important areas to work on right away – I need to be able to quickly locate my images and I need to make sure I have organized and secure backups. I’m in the process of documenting my personal workflow and it is forcing me to focus and deeply consider various aspects of naming, storing, tagging and managing my images.

Sell some photos
Some people have already expressed an interest in buying my work and I will oblige. In addition I plan to start shooting photos for jewelry designers and artists.

I hope to a little better with my resolutions this year. Check back to see!