What's in a Megapixel? (Part 1)

If you’ve ever visited my YouTube page you may notice a flurry of comments on a few of my videos by people who take issue with my claim that film is still superior to digital. Lately there were a couple of comments made regarding my “megapixel tours”, where I claim that a scanned frame of Medium Format film produces a file equivalent to 80 megapixels of detail. Oh boy were people pissed! To see one of the videos that started it all, check it out on the Video Feed page of my website (timhaines.com).

But here’s the thing. To understand the detail superiority of film, it’s important to note that “detail” implies a couple of things:

-Pixel Resolution of Color
-Pixel Resolution of Light/Tonal Capture (color and light)
-Pixel Resolution of Dynamic Range (You may understand this as brightness, contrast, hue, and saturation, shadow, mid-tones, and highlights. It’s “how much” color/light information can be captured).

Details, Details, Details...
It’s important to understand what we’re really talking about when we’re talking about “detail”. To say that digital pictures allow you to see into the pores of your subject’s skin or read the letters of a sign 200 meters away without the obstruction of film grain does not mean that digital cameras resolve more “detail” than film. To say that a digital image looks “sharp” does not mean that it has a lot of detail. All sharpness is is measurement of contrast between adjacent edges in a picture. Your eye interprets that as sharpness, but it’s only an illusion. When talking about detail, we’re talking about a camera’s ability to capture an image in a way that resembles--as closely as possible--how your eyes see it. This includes the accuracy and range of the capture of color, and range and accuracy of the capture of light. Color, light, and to what degree they can be captured. That’s what “detail” really is.

It’s difficult to illustrate this with digital images, because we judge the quality of digital images in terms of Megapixes, rather than values of color and light capture. What’s a megapixel? It’s detail. Right? Wrong! Megapixels is a factor of 1 million pixels, and it’s a measurement of how many pixels go into the construction of the image that you see on a screen. That construction happens in two distinct forms. Image capture (which is done by the sensor in your digital camera) and image display (the pixels pushed out of your video card, to be displayed on your monitor, which also uses pixels of its own to display the image)

Digital Capture
With digital photography, the game begins at the digital capture level. And the number of pixels wired into that sensor are critical. They’re like Lego pieces. The more Lego pieces you have, the more elaborate your creations can be. You’d build a much more elaborate Lego house with 500 Lego pieces than you could with 50 Lego pieces. And you’d build a much more elaborate Lego house with 5,000 Lego pieces. Pixels on your digital sensor work the same way. Each pixel is responsible for recording color and light information. The more of them you have, the more elaborate the reproduction of the scene your’e shooting. But all pixels are NOT created equal. A pixel’s ability to capture color and light data can vary greatly. The pixels in a $5,000 16 megapixel camera are engineered to gather light and color information much more effectively and efficiently than the pixels in a $150 point-and-shoot camera. So the number of pixels as well as the quality of the pixels is an important factor in digital photography.

Once color and light information is captured by the digital sensor, that information is then sent to the camera’s image processor, which generates the image that is saved to your memory card. You now have a digital picture! The size dimensions of the digital picture corresponds to the number of pixels used to capture it. So if you have a 16 megapixel sensor, you wind up with an image that’s made up of 16 million pixels--3,264 pixels wide, and 4896 pixels wide (3264x4896). How much “detail” is represented in those pixels depends on the quality of the pixels engineered in the digital sensor that recorded the image. Again, all pixels are NOT created equal. In a $150 camera, the pixels will just be ok. In a $5000 camera, those pixels will be engineered to capture much more detail per-pixel. So you can have two cameras, both capturing 16 megapixel images, but one of those cameras is going to capture a lot more detail than the other, even though their pixel count is the same. You dig? You’re starting to see why a 30 megapixel film scan is likely going to have more quality detail than a 30 megapixel digital image, but keep reading.


Digital Display
Now that you’ve captured your image, you’re going to want to look at it. Pixels are used for this purpose, too. But the job of these pixels is completely different from that of the pixels on your camera's sensor. For displaying your image, pixels are calculated by your video card, and pushed out onto your computer monitor. Your monitor doesn’t care what camera you used to capture your image. If you ask, it will tell you “Man, I don’t care what camera you used to capture your image.” Seriously, try it.
If you open a 16 megapixel image, it’s going to employ 16 million of its own pixels to rebuild and display the image according to the “instructions” your image provides. What instructions? You guessed it. Color, light, and the dynamic range of the color and light. Let me break it down again...
Your pixels captured color, light, and range data. But once again, all pixels are NOT created equal. Depending on your digital camera, those pixels captured that information like drunken sailors, or they captured that information like Spartan warriors. It all depends on the camera you used. Now it's up to your monitor to use DISPLAY pixels (not recording pixels) to display your image.

Now your computer (video card and monitor, specifically) is going to ask your image “What color, light, and range information do you have for me?” Your image will either say “bla, bluh blue, bla....colur...bla bla.....lite...blue blah....dinamyc raynge”, or your image will say “I declare this value of Blue, this value of Red, this value of Green. And Lo! I demand the display of said colors in accordance to the following ranges and values...” Your computer will take the “bla bla” instructions and reconstruct a bla bla image. Or your computer will take the Shakespearean Soliloquy instructions and display a much more beautiful image. And, again, the quality of those “instructions” depends on which camera you used, and the quality of the pixels used to record its image.

You can probably see already that when I say “My scanned frame of film equals 30 megapixels” I’m NOT saying “My film scan is the same as the detail captured by a 30 megapixel digital camera”. Why? Because....yet again...all pixels are not created equal. The ability to capture a wide range of color and light vary depending on the medium used (A Pro Digital SLR, a consumer digital point-and-shoot, or good ol’ film). And in the case of film, the image isn’t captured on pixels to begin with. So the "pixel" argument doesn't even apply. With film photography images are captured on grains of silver, which are much smaller, and more more efficient in capturing color and light than pixels are.

For more on this, stay tuned for part two of this blog post. Or, visit my website at www.timhaines.com, click "phoBLOGraphy" and read the post there. Blogs are always uploaded to my personal site first.

Be cool. Come back soon (or, check me out on my site)