Better yet, don't use MSPaint. There are lots of free
programs around. MSPaint is barebones. It won't even
let you choose the level of compression when saving
to JPG. The reason to use JPG is to get a smaller file.
(Or, occasionally, to send a picture to an Apple Seed
who can't read BMPs.)
There's little advantage to JPG if you can't even control
the file size/quality ratio. In the same vein, one
should never save to JPG until the final operation. In
other words, if you want to work on an image or edit
a photo, save as something "lossless" like BMP until
such time as you want to have a smaller file size in order
to send via email, post online, etc. Then save a copy
as JPG. (But don't do it in MSPaint.) If you handle images
in JPG format they will degrade. Each time you open
the file and resave it, at least a little of the data is lost
because JPG compression works by dropping out color
information. The compression scale is 1-100. (It's a
random number range; not percentage.)
If you save a BMP to JPG at, say, 80 compression you
will have a much smaller file that looks about as good as
the original. But if you then open and resave that file, each
time it drops out more data. Eventually the picture is so
bad that it is visibly composed of colored rectangles.
A lot of people think of JPG as a standard format because
digital cameras default to JPG. But that's not because JPG
is a good choice for photos. It's because JPG is usable on
all operating systems, it's relatively compact, and people
taking digital photos usually don't care very much about
image quality. If you're working with digital photos and don't
take pictures in RAW format then you should always save
your work-in-progress as something like BMP.
Possible editor options:
IrfanView is free and can handle just about anything
in terms of filters, resizing, etc. but doesn't have a
canvas to start from scratch.
If you want to draw from scratch there's the GIMP for
free. (Similar to Photoshop) and there are countless
simple programs for free. The free Paint.Net has also
had good reviews. I've never tried it as it requires .Net,
which is a massively bloated Java-type "virtual machine"
that Microsoft created. In other words, it's sort of like
an operating system within an operating system.
If you don't have the latest version of the .Net runtime
files installed then it means adding something like 1/2
GB of pointless bloat. But if you've already had to install
.Net 3.5 for some other reason then installing software
that depends on it is not a problem. In that case Paint.Net
might be worth a try.
http://en.wikipedia.org/wiki/Paint.NET