File Conversion
(I would think that GIMP may have this facility.... if not ....
don`t cry.... 
)download and install Irfanview. You will need to use WINE to get it to work on Linux
Open the PNG file,
Click FILE > Save as> then in the drop down box below you can choose the file extension you want.
Should be saved in the original folder location, with the new extension.
(I would think that GIMP may have this facility.... if not ....
don`t cry.... )
Like I said.......... 
Quote
(I would think that GIMP may have this facility.... if not ....
I thought that png and jpg were essentially the same format (except that png has a transparent bit so that it doesn't have to display in a rectangle. Try simply changing the extension from filexx.png to filexx.jpg 
John
edit: tried it and although it displays properly in preview my photo software wouldn't open it - sorry.
J
EDIT: but you can insert it into a document in the usual way.
J
John
edit: tried it and although it displays properly in preview my photo software wouldn't open it - sorry.
J
EDIT: but you can insert it into a document in the usual way.
J
works for me - although GIMP would do it better.
Quote
Quote from: HighLordPhanty png and jpg are completely different formats.
png is lossless, jpg is lossy.
Changing file extensions is not clever
I'll consider myself chastised and go and sit on the naughty step.
In fairness, I never said it was clever, only that it seemed to work, and if it didn't you only have to change the extension back again
Quote
One way to incorporate such metadata, often associated with Unix and its derivatives, is just to store a "magic number" inside the file itself.
Originally, this term was used for a specific set of 2-byte identifiers at the beginning of a file, but since any undecoded binary sequence can be regarded as a number,
any feature of a file format which uniquely distinguishes it can be used for identification.
GIF images, for instance, always begin with the ASCII representation of either GIF87a or GIF89a, depending upon the standard to which they adhere.
The magic number approach offers better guarantees that the format will be identified correctly, and can often determine more precise information about the file.
Since reasonably reliable "magic number" tests can be fairly complex, and each file must effectively be tested against every possibility in the magic database,
this approach is relatively inefficient, especially for displaying large lists of files (in contrast, filename and metadata-based methods need check only one piece of data,
and match it against a sorted index). Also, data must be read from the file itself, increasing latency as opposed to metadata stored in the directory.
Where filetypes don't lend themselves to recognition in this way, the system must fall back to metadata.
It is, however, the best way for a program to check if a file it has been told to process is of the correct format: while the file's name or metadata may be altered
independently of its content, failing a well-designed magic number test is a pretty sure sign that the file is either corrupt or of the wrong type.
On the other hand a valid magic number does not guarantee that the file is not corrupt or of a wrong type.
So-called shebang lines in script files are a special case of magic numbers.
Here, the magic number is human-readable text that identifies a specific command interpreter and options to be passed to the command interpreter.
Another operating system using magic numbers is AmigaOS, where magic numbers were called "Magic Cookies" and were adopted as a standard system
to recognize executables in Hunk executable file format and also to let single programs, tools and utilities deal automatically with their saved data files,
or any other kind of file types when saving and loading data. This system was then enhanced with the Amiga standard Datatype recognition system.
Another method was the FourCC method, originating in OSType on Macintosh, later adapted by Interchange File Format (IFF) and derivatives.
See Wikipedia...