A *.jpg file how is it constructed?

Question

I know a *.jpg file has layers in it, how many of them does it have? What they are for?

Who created the *.jpg as we know it.

Answer 1

The Independent JPEG Group, defined the standard.

JPEG itself specifies only how an image is transformed into a stream of bytes, but not how those bytes are encapsulated in any particular storage medium. A further standard, created by the Independent JPEG Group, called JFIF (JPEG File Interchange Format) specifies how to produce a file suitable for computer storage and transmission (such as over the Internet) from a JPEG stream.

Full info at http://en.wikipedia.org/wiki/Jpg#Encoding.

Layers are constructed as part of the image editing stage of editing an image. Where bits are stuck on top of one another like a cake - sponge then cream, then sponge, then more cream, then strawberries :p

Photoshop and Paint Shop Pro both allow you to create layers. Once you save it asn a JPEG, the layers are flattened to produce just one image.

Answer 2

to the best of my knowledge, *.jpg files cannot hold multiple layers at all, only one layer.

animated *.gif files contain layers which are played in sequence.

*.psp/*.psd and other 'proprietary' image formats can hold multiple layers and other information but are generally saved as a more common format before being uploaded onto the web.

it was 'invented' by the 'Joint Photographic Experts Group'.

ps - did your numbers-to-text excel code work? ;)

Answer 3

Try on wiki
http://en.wikipedia.org/wiki/Jpeg