I have a Casio EX-S12. It has a setting for image size, but also a separate setting for what it calls "image quality". There are three image quality values: "Fine", "Normal", and "Economy".
The Casio manual is not clear on what image "quality" actually means -- specifically how it's different from image size. All they say is that the "Fine" setting "helps to bring out details when shooting a finely detailed image of nature that includes dense tree branches or leaves, or an image of a complex pattern." I'm confused because isn't this what image size is all about (more pixels = more detail)?
In terms of memory usage, the manual also says that for a 5 megapixel picture, a "Fine" image takes up 2.99 MB, a "Normal" image takes up 1.62 MB, and an "Economy" image takes up 1.12 MB, so this "image quality" setting of theirs is certainly having a significant impact on memory usage.
My question is, what exactly is "image quality", if it's not image size? What is the "thing" that is taking up additional memory?
Thank you.
Answer
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.
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