Compression

[markookram]

As you can see I have a wireframe picture without any background and trying to save it to a .jpg. Why do other gray squares appear on the preview on the left? It should be all white since I have no background?

http://www2.arnes.si/~mocko/psp.jpg

[MWCinNY]

my guess would be jpeg artifacts from compressing it.

[markookram]

Why does that happen? Why is he compressing "all white" into "white with gray dots"?

And more importantly how do I convince him he should only compress the wireframe part without smudging everything around it?

[coningham]

JPEGs are awful for dealing with large areas of one color, especially with the compression set to a very high value - if you set it to 1 you would see a lot of improvement, but then the file size would increase a lot.

There are two other formats that you could use instead: GIF and PNG.
GIFs only support 256 colors, which is fine if all you have is lineart.
PNGs can either save to up 256 colors (8 bit) or 16 million color (16 bit I believe). If set as 16 million the file size would be much larger than the JPEG one, although you would have the ability to save a transparent background instead of getting a white one.

[markookram]

Thanks for the reply. Seems like I have alot to learn.

[MWCinNY]

Why does that happen? Why is he compressing "all white" into "white with gray dots"?

And more importantly how do I convince him he should only compress the wireframe part without smudging everything around it?

im not sure why it would need to be compressed when it was only 16k anyways, and im not sure if the wireframe is the final image or not, but if it isnt, then why compress it in the first place? the smudging will also make it appear like that too. im not sure why you would smudge the edges of a wireframe, but if you want to clean the lines up a little, i would use a small soften brush instead and set the hardness and opacity to about 50. if that dont look the way you want it to, then adjust the settings some until it does.

i never compress any images unless i am sending them through email, and i never compress the original or an unfinished piece of work.

like coningham said, you can also use the PNG format, but the file size will be alot larger. and just to clarify things, PNGs are saved at 16 million colors/24 bit, not 16.

[markookram]

That's 16 MB hehe.

The picture needs to be in a .jpg format. But I wanted to compress because it will be transfered and loaded between users alot. But I guess 1 MB is not so bad for a 2048*2048 picture so I'm happy.