How does thumbnail of each image is created

Question

In Android gallery app, how does the thumbnail of each image is created? Is it embedded in the JPEG header of the image? And the thumbnail was created when the picture is taken by jpeg encoding library?

Of the thumbnail is created on the fly when the image is loaded by Android gallery app?

Thank you.

Answer 1

Thumbnails are cached on Android, so they don't have to be created on the fly every time you look at the images.

As for generating them on the fly, the gallery can definitely do it. At the very least it does show me thumbnails of the images that didn't have any embedded thumbnails.

Embedded thumbnails do exist, but I have no clue whether the gallery takes advantage of them.