What’s the difference between image size and image quality on a camera?

Asked 8/4/2011

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My Casio EX-S12 has separate settings for image size and image quality. Image size seems straightforward because it changes the number of pixels, but the quality options are Fine, Normal, and Economy, and the manual doesn’t clearly explain what that means.

For example, the manual says a 5 MP image uses about 2.99 MB at Fine, 1.62 MB at Normal, and 1.12 MB at Economy. If the pixel dimensions stay the same, what is the camera changing to affect file size so much? How is image quality different from image size?

compression point-and-shoot jpeg image-size image-quality

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

15y ago

2 Answers

Image size is what if often called resolution, basically the number of pixels stored in the image file. So on a 12 megapixel camera, you can usually choose between 12 MP, 6 MP and 3 MP or similar values.

Image quality is independent of size and is usually called compression. This controls how much information is discarded from images while they are saved.

You can read this article which I wrote several years ago for a comparison between the two.

Originally by user1620. Source · Licensed CC BY-SA 4.0

user1620

15y ago

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Image size and image quality control two different things.

Image size = the number of pixels in the photo (resolution), such as 12 MP, 6 MP, or 3 MP.
Image quality on cameras like this usually means the amount of JPEG compression used when saving the file.

JPEG is a lossy format, which means it reduces file size by discarding some image information. A higher-quality setting like Fine uses less compression, keeps more detail, and creates a larger file. Economy uses more compression, throws away more data, and creates a smaller file, even though the photo still has the same pixel dimensions.

That’s why a 5 MP image can have very different file sizes depending on the quality setting: the “extra memory” is being used to store more of the original image data with less compression.

In practice, higher JPEG compression can reduce fine detail and introduce artifacts, especially in complex scenes like leaves, branches, or patterns. If storage space isn’t a major concern, it’s usually best to use the largest image size and the highest quality setting.

What’s the difference between image size and image quality on a camera?

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