Best format for pictures?

[J13]

I was just hoping to find out about this now rather then have to convert all images i want to use later.
Basically i'm looking for 2 things, the first being the best image format to use (Jpeg, png, bmp etc) which ren'py supports, allows transparency and has a good image quality to size ratio.
The second is the best format to use for smaller and/or less detailed images, also supported by Ren'py, in this case it doesn't need to allow transparency nor does the image quality to size ratio have to be great, i'm juts looking to keep the image file small with this.
For what i've done so far i've used .png and while the file sizes are thankfully relatively small i'd still like to get them smaller if at all possible.
Any help would be appreciated as i simply don't know what to look for witht his sort of thing.

[chisa-chan]

JPEG and BMP is good, but seems it needs alpha-layer mask to allow transparency. Not sure if Ren'Py supports this, though.

If you want your image to appear in alpha / transparent in Ren'Py, use PNG format (set the background to transparent)

Ara, JPEG can be kept small. Set the image quality around 7 (medium), it won't look so different with the high quality ^^

[monele]

Just confirming : PNG for transparency and lossless quality, JPG for anything else.

[Jake]

Also: PNG can do significantly better filesize-wise than JPEG if you have a lot of flat colour in an image, but it doesn't cope so well with gradients. So if your BGs (for example) are simple, it's worth checking if they're smaller as PNGs.

Also also: even at high quality levels, JPEG makes a terrible job of high-contrast areas, like the edges of hard lines and text, so if you have a lot of those in your image it's sometimes wiser to use PNG anyway.

I can't think of any reason you'd ever want to use straight-up BMPs for anything, though.

[J13]

Well i tried converting a bunch of images to .jpg and it was just as you wrote, single color (or near enough) images tended to either gain size or only be slightly smaller. But with multicolored images, converting to .jpg seems to have reduced the size by about a 1/5th without a noticable loss in quality.
Either way i'm happy so thankyou for the info/advice.

[DaFool]

jpg backgrounds / full-screen images
png sprites / overlays with transparencies

[chronoluminaire]

jpg backgrounds / full-screen images
png sprites / overlays with transparencies

I wouldn't say it's quite that. It's not based on resolution per se, but image content:

PNG for things with transparency, large blocks of the same colour, or things with high-contrast edges (like text) that you don't want to blur... basically almost everything except photos
JPG for cases where the above don't apply: principally photos.

[rioka]

I'm with the jpg - backgrounds; png - transparencies crowd too.

...Though I have used gif on some background images to cut down on file size. Does that make me a traitor now? D:

[PyTom]

No, although I'd be surprised if you found a case where a GIF is superior to an 8-bit PNG in file size, when the PNG has been saved with level 9 compression, and optimized using a tool like pngcrush.

(I mean, genuinely surprised... although I haven't studied it in much detail, PNG is the newer format, and should generally have better compression than GIF, when both represent 8-bit images.)