Amiga Inc. announces new hardware

[AlexJ]

Actually that is a misunderstood thing about PNG. It actually supports both lossless and lossy formats, and allows the saving of up to 256 colour lossless images with transparency, or up to full colour 24bit lossy images, all within the single format. Therefore it is really the only format that would be needed for anything online if only it was supported by every browser.

Really? I thought (and from experience have always found) it to be a lossless compression at both 256 and 24bit.

Edit: Just checked it's Wikipedia page - no mention of it being lossy. Also did a test - a 1.17MB 24bit BMP file, shrunk to a 129KB 24bit PNG file. The same BMP file when added to a zip file compressed to 115KB (zip of course is lossless compression). Therefore as there is less that 15KB difference, I believe that PNG is also lossless.

Edit2: I'm now convinced you're wrong Harrison! I found the official specification for PNG. Quote: "There is no lossy compression in PNG. Existing formats such as JFIF already handle lossy compression well. Furthermore, available lossy compression methods (e.g., JPEG) are far from foolproof --- a poor choice of quality level can ruin an image. To avoid user confusion and unintentional loss of information, we feel it is best to keep lossy and lossless formats strictly separate."

[Harrison]

I think that all commercial applications do only support the lossless part of PNG, where 8bit PNG saves a colour palette and references it per pixel, and 24bit PNG saves 3bits per pixel to save the exact colour data on a pixel for pixel basis. Lossy compression is supported as being possible with the PNG format but hasn't been implemented outside of research.

I also forgot to mention that PNG also supports alpha channels which is a huge advantage of both gif and jpg as you can save a true 8bit alpha channel that can be used as a mask for varialbe transparency when used with another image. This is great for gradiant shadows often seen in web graphics. Sadly this isn't used much as IE doesn't support this at all and will cause a broken image error when tried.

Another cool feature of PNG is variable compression within a single file. PNG contains five compression filters and a different one can be associated with each pixel line of an image. This is a great feature as lines with a lot of differing colour data will compress differently to only with hardly any changes such as sky or a solid area of colour.