Understanding Image Aspect Ratio

Image Aspect Ratio Cover
Image Aspect Ratio Side
Image aspect ratio is the proportional relationship between the width (x) and the height (y) of an image. It is commonly expressed as two numbers separated by a colon (x:y), as in 3:2, 4:5, or 16:9. This ratio is applied universally across all image formats regardless of the actual size of the image, big or small, and its main use is in the presentation of videography aspect ratios of films in cinemas, still camera photography, and television, DVD, and Blu-ray Disc display formats.

The most common aspect ratio in still photography today is 3:2, which is based on the image size of 24x36mm captured on 35mm film cameras.

This image aspect has been carried over to digital photography with image sensors manufactured in the same aspect proportion, be it a full frame or APS-C sized sensors. Micro four-thirds and a range of compact digital cameras are fitted with 4:3 aspect ratio sensors. Current smartphones tend to capture images in the 16:9 aspect.

Quick Lesson 4: Understanding Image Aspect Ratio
3:2 Image Aspect Ratio
Aspect Ratio 3:2
The standard image aspect ratio as found on all 35mm film cameras and digital camera derivates that are fitted with full frame, APS-C, and APS-H sized sensors. This aspect ratio was first introduced by Oskar Barnack for Leica cameras early in the 20th century.

3:4 Image Aspect Ratio
Aspect Ratio 3:4
A very uncommon ratio, a product of the half frame 35mm film cameras where the image captured is half the size of a standard 24x36mm film frame. Normally designed to shot in the portrait or vertical mode, the image negative image of half frame cameras is 14x24mm.

1:1 Image Aspect Ratio
Aspect Ratio 1:1
The traditional square format, made famous by the Rolleiflexes, Hasselblads, and Pentacon Six TL. It's also used by toy cameras like the Holga and Diana. The only 35mm square image producers left are plastic cameras made by Lomo and the curious Blackbird 35mm twin lens reflex camera.

4:3 Image Aspect Ratio
Aspect Ratio 4:3
Used by micro four-thirds cameras, most compact cameras, digital medium format cameras and medium format film cameras that use the 6x4.5cm format.

5:4 Image Aspect Ratio
Aspect Ratio 54
Used by large format cameras which use sheet film in 5x4 inch or 10x8 inch sizes.

7:6 Image Aspect Ratio
Aspect Ratio 7:6
Used by medium format cameras in the likes of Pentax 67 film camera series and the rangefinder Mamiya 7II. Negatives measures 6x7 centimeters.

16:9 Image Aspect Ratio
Aspect Ratio 16:9
This panoramic format is used by some medium format panoramic film cameras and many current smartphone cameras.

In-camera setting
Many recent digital cameras come with a function that can change the aspect ratio of the image you are shooting. The availability of this function does permit a level of creative flexibility in the framing and composition of a photograph.

You must remember that if you are capturing the image in JPEG, the image will be cropped to that aspect and there is no reverse in the process. Shoot the image in RAW instead, where the image is saved as captured by the entire sensor and do your crop and other edits in post-processing.

Resource Links:
Aspect Ratio: What it is and Why it Matters
An Introduction to Aspect Ratios and Compositional Theory

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