Ben
Favorite Answer
PNGs are lossless compression, so the files look better than JPEGs. They support transparency, so not every picture needs to be a square.
In addition, PNGs have an interesting history. It used to be that there were two main formats for pictures on the Internet: JPEG and GIF. Then, CompuServe, which owned some patents related to GIFs wanted to charge everyone who put GIFs on their site. So people made PNGs instead. This reason isn't relevant any more- the patents for GIFs have expired so you can use the format without worries, but it used to be a big deal.
possum
There are many kinds of images, but two broad categories are called "lossy" and "lossless". They refer to what happens when you edit and save the image over and over. In lossy formats, in order to achieve best compression, two pixels are compared. Normally, in lossless, if they are different in any way, they are not considered identical. But in lossy formats, two pixels who are similar - but not identical - in color are considered the same when saving and compressing. When rendering this image, the two adjacent pixels are displayed - but not in the original color. Depending on the algorithm, the two are the exact same color, but, they cannot be distinguished. So, one pixel can never be recovered to it's original color. Most humans cannot distinquish between these differences, and so this is usually an acceptable loss. When it isn't acceptable, then JPEG (and other common lossy formats) should not be used. PNG is a lossless format, and can be used. It won't compress as well as JPEG, but this is the tradeoff.
You can imagine the problem here. Say you have a 3-pixel image. Pixels A, B, and C are similar in color and are next to each other. The algorithm will compress A and B together, because they are similar, Assume C is left alone, because although it's similar to B, but B was already approximated to A, C is left alone.
Next day, you edit and save the image again. Pixels A and B are the same, and cannot be distinguished between them as they could yesterday when they were different. And so when saved, neither are approximated. But B and C are similar, and so one gets approximated to the other. It could be that B is approximated to C, or C is approximated to B - much depends on other factors designed into the algorithm. Over time (maybe lots of time) a JPEG image can be saved and resaved so many time that eventually, all pixels are the same color, or at least, the original image is completely unintelligible.
So that's why you need to be careful about whether you use lossy or lossless. PNG doesn't compress as well as JPEG, but it will preserve everything. Also, the PNG format is transportable to many more platforms than JPEG. JPEG, with compression algorithms JBIG and JPEG2000, is not necessarily compatible with all platforms or all readers. PNG guarantees that. Just because an application can say it reads JPEG files, doesn't mean it can process JPEG files with JBIG or JPEG2000 compression.
Anonymous
I recently learned in pse 8 you can save an image as a png 24 so it has a transparent background! Example: photo of a person/object that you like, but not the bg. extract what you like copy and paste to a new file with a transparent bg and save for the WEB as a png 24 and save. now you have just that image to use on whatever you want. i used my daughter's image and merged with butterfly wings then extracted that into a picture of flowers. email me if you have any questions.
green meklar
PNG uses lossless compression. As a result, although it usually ends up with larger images than JPG, it preserves all the original image information perfectly and is still smaller (for almost every type of image) than something like BMP. It is particularly good for images that contain large areas of similar colors. Also, unlike JPG and GIF, PNG supports 8-bit transparency, so you can have partly transparent areas of an image. Personally I use PNG for almost everything, except when I need animation in which case I use GIF.
Anonymous
according to my research PNG stands for Portable Network Graphics (PNG) it is a bitmapped image format that employs lossless data compression. PNG was created to improve upon and replace graphics and pixels hope this helps!!!