Subtitles of the Movie

Welcome to this lesson on image compression. I've got several images in the Organizer here and I'd like to walk through some concepts about image compression in one lesson to kind of put them all together. There are two types of image compression: one is lossy, which means essentially you take the original image and you average groups of pixels into one color and as you can see from this JPEG that's compressed at 80 percent, you end up with blocks of pixels which you can see the banding there in each row and column and that's to save space. If you zoom out, the further out you go actually the less obvious the compression is. So there's a point to having this and it's not just to look bad. For example, if you compress something at 80 percent and have a magnification reduced, for example, at this level, that would be a wise choice. You're saving space, you're saving size and nobody can really tell the difference. However, if you zoom in and you can see the level of detail as I see here, then it would be either a bad choice from an aesthetic point of view or perhaps a really good choice if you're trying to get a point across quickly and with a low file size and you don't need as much image fidelity. This is called lossy compression. The original JPEG, if I can go up here, JPEG 01, this is the original JPEG. You can zoom in here and up to the limits of the camera resolution and post processing, you can see quite a bit of fine detail. Eventually any image will start to pixelate if you zoom in far enough. So the point is to reduce the file size. Let's check that out. JPEG 01, let's go to Image, Image Information, we can see that it's 826 kilobytes on disk. Now, let's compare that to the 80 percent; 826 kilobytes compared to 45 kilobytes. That is quite a big difference. Now, with jpeg, there are different levels of compression that you can apply, ranging from one to 99. One is essentially the least amount of compression you can apply, but don't get caught into thinking that you're not losing anything. If I were to take this photo as a final product and continue to save it as a JPEG over and over and over and over again, I'm still compressing that every time. No matter how low the compression level is, it is still compressing. Here is JPEG 14 which is at a 14 percent compression ratio and that looks pretty good. So there are different compression levels in JPEG that make, and here's a 50 percent which you can start to see the results. There are different compression settings in jpegs that, that you can use for different purposes. Mathematically again, the jpeg file type uses an algorithm to average pixels together and come up with a way to squeeze out extra bits. Alright. The other type of compression is lossless compression, which reduces files by less of a percentage because you're concerned with image quality there. So let's take a look at the tiff uncompressed. Again, this is similar to the JPEG 01, however there is no compression and no loss here in this image whatsoever. Very high quality. Now, if I open up tiff LZW, look at this. This is compressed but due to the way tiffs work, it's not a lossy compression; it is lossless so when I zoom in at this level, I get the same image. The difference is in how the bits are stored. So if we look at the file sizes, image information for the LZW, we get about a meg and a half on disk. Let's look at uncompressed. About twice as much; over three megabytes. So in this case, we're saving half the space at no cost in image quality. This is a good trade-off. The down side to tiffs is they are not compatible with web browsing. You really have to use jpegs, gifs or pngs. However, they're great for printing and using on your computer. Now let's look at some pngs. I did two pngs and again, pngs are lossless compression; 16 million colors. We're looking at a meg and a half and here we're looking at limited palette PNG, 444K. So a combination of the png's lossless compression with reduced palette reduces this image down quite a bit. Finally, there's compression also in your Paint Shop Pro images and here I'm just going to let my mouse hover over this. This is an uncompressed image. It's huge. I'll just pop out to Windows Explorer here. This file is 222 megabytes. You can see down here in the status bar. That's uncompressed. That's the original. And then we come over here to LZ77, 56.6 megabytes, 82.0 megabytes for the RLE and then again, the uncompressed version is 222 megabytes. So with Paint Shop Pro files, depending on your needs, you can compress them at a lossless quality, not suffer any ill effects and reduce your file size. Alright. I think I better wrap this lesson up. That is some information on image compression.