GuessTheFormat is an experiment for photographers: can you tell the difference between camera sensor formats just by looking at a photo?

Does sensor format really matter as much as many photographers think it does? Is an image from a full-frame camera really distinguishable from one taken with an APS-C camera? Perhaps not as easily as you think.

Head over to the photo page to test your identification skills, or check out the stats page to see how different formats measure up against each other.

GuessTheFormat indexes photos from Flickr Explore. During indexing, the camera sensor format of each image is derived from the EXIF data. During the guessing phase on the photo page, a random photo from the indexed repository is shown and presented along with two image sensor formats: a correct format, and a random incorrect format. The player's challenge is to examine the photo and try to select the correct format. Results are recorded, aggregated regularly, and presented on the stats page.

The image sensor is the part of a camera that captures the light coming through the lens, and records it as a picture. It's the film of a digital camera! Image sensors come in many different sizes and aspect ratios. Many common shapes and sizes get classified into standard "formats".

For example, a digital camera with a sensor the same shape and size as an old 35mm film camera is called a "full-frame" format camera. "Full-frame" cameras have relatively large sensors compared to most other digital cameras. A "compact" camera, for instance, has an image sensor that's a tiny fraction of the area of a "full-frame" sensor.

The common belief is that larger sensors are always better than smaller sensors. Indeed, large sensors (full-frame, APS-C) typically have much better image quality than small sensors (four-thirds, compact). However, smaller sensors have their advantages too: lower cost and smaller overall camera size. In fact, a camera with a smaller sensor may produce images that are indistinguishable from those created with a larger sensor camera...especially in the hands of a capable photographer!

For more information about camera sensor formats, have a look at the Wikipedia links below:

I, too, love pixel-peeping. However, the fact is that most images taken nowadays are destined for social sharing on the web, where they will be viewed at fairly modest resolutions. Viewing at 100% resolution makes format identification slightly easier to the trained eye, but it's simply not practical for this exercise. Why not try to guess the format at a resolution that most people will view the image at?

I've omitted common formats that are not often found on Flickr. For example, iPhone images are classified into the "camera phone" format, but they are so rare in Flickr Explore that they are not worth displaying. Images from cameras with one-inch sensors (like the Sony RX100 or Nikon 1 series), and APS-H sensors (like the Leica M8 and the older Canon 1D series) are omitted as well.

I am very strict about classifying the format of the image sensor, not the camera. For example, the Nikon Coolpix A camera is the size of a small point-and-shoot, but it has a DX sensor, therefore it is classified as an APS-C format camera. Sigma's 1.7x crop Foveon-sensor cameras are classified as APS-C as well.

No. Formats are chosen with uniform probability: a random format is selected first, then an image with that format is randomly chosen. In theory, you have a 50/50 chance of choosing the correct format if you always go for the format that's displayed on the left (or right). This is the other reason that uncommon formats cannot be displayed: their photos would repeat far more often than common formats.

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Who are you?

My name is Michal Cialowicz, and I am a photographer and software engineer. Besides photography and software development, I love the outdoors, hiking, camping, traveling, epic motorcycle journeys, and SCUBA diving. I live in San Francisco, for now.

Check out my website, have a look at some of my photos on Flickr, and follow me on Twitter!