How to blow up image without graining

[Nathan4102]

I'm working on a game right now, and at the moment, I'm working on the graphics. At first, I was going to do 20x20 tiles, but I decided thats a bit small, and I should blow it all up to 40x40. The problem is that I've already made a lot of my graphics, and redoing them all on a 40x40 image would take hours. Like a lot of hours. :p

So what I want to do is create my images in 20x20, and then blow it up to 40x40, but I can't seem to make it work. Using the zoom in feature in my photoshop (CS2) I can see what the 40x40 would look like in perfect quality, exactly how I need it. But then when I try to resize the image using "Image size...", it blurs it! I don't know a lot about photoshop, but I'm guessing that since I can see the 40x40 version with zoom, it SHOULD be possible to save it like that.

So if any of you guys know how I would go about doing this, please let me know! And also, please don't use crazy technical (or even kind of technical) photoshop terms, all I use it for is pixel graphics and basic editing.

I've also attatched an example tile from my game, in psd format, in case you need to see how it's done or something.

Thanks,
Nathan

http://www.2shared.com/photo/lp3J_UgV/Building1.html

[DemonWasp]

When you scale the image, change "Interpolation" to "None" (which will use the colour of the nearest pixel from the source) rather than "Cubic" (which will "blur" things as it tries to avoid distorting the image by choosing values "between" two pixels).

Note that this only really works if you're scaling up by an even multiple. Scaling down will go poorly, as will scaling by non-integral numbers like 2.5 or 3.3 .

I tried this in GIMP, so the exact instructions may vary in Photoshop.

[andrew.]

If you don't want to resize each image manually in an editor, take a look at ImageMagick. You should be able to write a script to batch resize all your images.