You won't kill your bandwidth as quick with PNG. As smitty pointed out, file size is the key difference. Just use PNG and forget BMP for the time being [grin]

I use PNG almost exclusively as my image/texture format for basically the same two reasons mentioned above. PNG is compressed so the overall size of you game (or app) will be smaller when you go to distribute it. PNG also has an alpha channel which allows for gradient transparency as opposed to binary transparency. (aka. transparent or opaque)
Other than the fact that the code to load PNG files is more complex, i dont see any disadvantages compared to BMP.

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Stevo

The two main reasons, as have been said, are transparancy and compression. PNG is nice because it can have transparancy built-in, while adding transparancy to a bitmap is really a bit of a hack, and not supported by many editors. PNG compresses nicely because it has several compression methods at its disposal Some work better for flat-shaded images (cartoons, limited color images) while others work better for more realistic scenes (textures, photos); PNG chooses the best one. The net result is that simple images often compress better than GIFs, while more complex images offer compression very close to JPEG, with similar visual quality.

The main benefit that BMP offers over PNG and most other formats is that it is incredibly simple to load, since its essentially a memory-image of the graphic data plus a small header. PNG and other compressed formats require a loader to de-compress the image as its loaded, making the loader more difficult to write. That said, there are very mature, free loaders for nearly every image format, including PNG.

TGA is another nice format that was/is common in games. In many ways, TGA is a middle-ground as it supports transparancy, is easier to load than PNG, but doesn't compress as well.

Quote:Original post by teebee
Also loading PNG:s takes much longer, so if have loads of images and your application needs to be loaded as quickly as possible, you might want to consider another format.

I suspect that's not entirely cut-and-dried. Disk access is incredibly slow compared to memory accesses and computation. A Typical processor runs about 40 million cycles in the time it takes to read 1MB of data from a hard drive (assuming 60MB/s transfer, which is a pretty generous estimate). The question becomes "Does it take longer to load 2 or 3 times as much data, or to decompress less data.)

There's likely many factors - Hard-drive speed, fragmentation of the file then there's the contents of the image and how well it was compressed and how easily it is uncompressed.


Your assertion is likely true for small images that, for whatever reason, generated a file exhibiting decompression requirements that approach worst-case.

I presume that the average case is comperable to, or better than, bitmap, but most certainly not "much longer".