Over the years, I’ve been asked many times about a topic that seems simple to those of us who do a lot of image manipulation, but remains a challenge to explain to the novice. So, I’m going to take a stab at it, and if I can conjure up a decent explanation, then I’ll have a place to send people who ask in the future. The general question is about the relationships between document size, resolution (ppi or dpi), and pixel dimensions. You see? It already sounds confusing—I’ve got my work cut out for me.

Because this is a fairly broad topic (and because I can think of many different examples to illustrate it), I will be breaking the explanations down into separate posts. Hopefully by the time I’m finished, it will all fit together and make perfect sense. To get started, I’ll cover the basics of a digital image.

Digital Imaging Basics

For this series of posts, I will be discussing what we call “bitmapped” images. This simply means that the image is made up of a grid of dots, and this applies to all digital photos. Adobe Photoshop is a bitmapped image editor. The other kind of image (non-bitmapped) is called a “vector” image, and Adobe Illustrator is an example of a vector image editor.

The smallest element of any bitmapped digital image is the pixel (a loose abbreviation for Picture Element), which appears as a single colored dot on the screen.  An image is composed of a grid of pixels with a certain number of rows and columns. Back in the ’80s, early IBM PCs were sold with a video card called a “versatile graphics adapter,” or VGA. This card was designed to drive a color display with 480 rows of pixels, with 640 pixels in each row. Today, video cards are much more advanced, but we still sometimes use the acronym VGA to refer to those pixel dimensions (640×480).

A digital photo, or any other digital image, can be any size you want, but they all have a rectangular grid of pixels (including any transparent pixels). The more pixels the image contains, the more detail you can see. Icons that appear on a Windows desktop are typically 32 rows of 32 pixels. These can be referred to as 32×32-pixel images. Images taken on a 2MP (MegaPixel) iPhone camera are 1600×1200 pixels. Images from my 10MP Canon 40D are 3892×2586 pixels. If you ignore all other aspects of document size and resolution and assume that all pixels are the same size, it should be clear that the fundamental rule of digital images is that an image with more pixels will be larger and more detailed than others with fewer pixels. Here is a small image represented by four different pixel dimensions.

In each of these four images, the pixels are all exactly the same size (determined by your video monitor), but each image uses a different number of them. The more pixels an image has, the more detail you can see in the image.

The next post will discuss pixel size and what happens when the pixels are not all the same size.

Wow! You can believe the hype. The iPhone is the coolest technogeek toy for as long as I can remember. Truly the “Internet in your pocket.” Now, I look forward to the day when all public buildings will have free, open WiFi, because the EDGE network is a bit too slow for my taste, but it works well enough. I am writing this post from my iPhone while waiting in my car—not because I need to, but because I can! Now I need to post this so I can go buy more AAPL stock.

While on vacation last summer, I had the opportunity to borrow some “L” glass from a friend who rented it and then loaned it to me for a few hours. It was a Canon EF 24-70mm f/2.8L lens, which was most similar to my Canon EF-S 17-85 f/4-5.6 IS. As long as I had the opportunity to try it out, I thought I’d go ahead and set up a comparison test to satisfy my curiosity. I’d been wondering whether the extra cost of the “L” glass was worth it, or even really noticeable. You can find comments online about how the L glass is sharper, or produces better color or contrast, but I have never seen comparison shots that prove it. (If you know of any such comparison shots posted online, please post a comment with the URL.)

Anyway, I set up my tripod and framed an image with the L glass first, and set the focal length to about 70mm (zoomed all the way in). I focused on some particular petals in a flower box side-lit by early evening sunlight, and squeezed the remote trigger to take the picture. Then, I replaced the lens with my non-L glass, tried to eyeball the same framing as best I could, then focused on the same flower and squeezed off another shot.

Both shots were recorded in RAW mode in my Canon 30D, and exposed at f/8 at 1/60. When I opened them in Photoshop, I could definitely tell that something had changed between the two shots, but it mostly seemed to be differences in framing and camera position. (The L lens is noticeably heavier than the non-L lens, and it’s a bit longer, which gives a slightly different perspective on the scene.) But, was there a difference in sharpness? Not that I could see. Color saturation or contrast? Maybe, but not significantly, and any difference could have been attributable to the change in the sunlight over the few minutes between shots.

My conclusion is that I could not find any reason to spend the extra money on the L glass as long as a non-L equivalent was available. The difference in image quality would be lost on me, and I have a very discerning eye for detail. The exceptions, of course, would be where a particular focal length or maximum aperture was only available in an L version. But as long as there is a non-L lens available for the work I do, I’ll stick with the more affordable options. Again, I invite readers to post comments with links to any relevant comparisons between L and non-L lenses, especially if they demonstrate a significant difference.

I’m trying to overcome my inertia to get going with some meaningful posts, and I thought it would be useful to start by posting some things I’ve been thinking about, which may end up as new articles. Here we go!

• Canon’s expensive “L” lenses — worth the money?
• Architectural Photography
• Ideas for Wide Angle lenses
• Ideas for Macro lenses
• Gaining cooperation from reluctant subjects (family)
• Studio lighting

For lack of a more creative title, I’ve decided to call the official Livingstudios blog “Studio Notes.” For a while, don’t expect anything too exciting, as I will be busy trying to make this thing look less ugly. I also need to figure out why I have a blog in the first place, which would be a prerequisite to posting meaningful entries. So far, here are my thoughts about what this blog may contain:

• interesting photos with comments about exposure, lighting, composition, etc.
• puzzling photography issues I’ve struggled with and how I’ve solved them (IF I’ve solved them)
• commentary about graphic designs, logos, and other commercial branding issues
• platform evangelism (I’m a Mac user)
• anything else that I feel like rambling about.