Lossy compression reduces file size by removing unnecessary bits of information. This type of compression is most commonly used on image, video, and audio files, where a perfect representation of the source media is not required. Since the average human ear would not notice this difference, the result is a smaller file with minimal user impact.
The downside? The more heavily a file is compressed with lossy compression, the more noticeable the reduction in quality becomes. Also, lossy compression does not work well with files where all of the data is crucial for example, compressing a spreadsheet would yield unusable results. Lossless compression reduces file size without removing any bits of information.
Instead, this format works by removing redundancies within data to reduce the overall file size. With lossless, it is possible to perfectly reconstruct the original file. For example, the most common lossless compression format ZIP is often used for program files in Windows, as it preserves all the original information. The men in this study first ran on treadmills wearing no compression and then a second time while sporting compression sleeves on their lower legs.
Researchers measured their oxygen uptake, stride, body positioning, and other markers throughout both runs. They noted no difference in exercise efficiency or biomechanics between the compression and no-compression runs.
This lack of effectiveness flies in the face of the claims often made about compression clothing, by both their manufacturers and users. For example, Stickford says, the garments used in her study supposedly increase blood circulation — and, thus, oxygen delivery — for improved sports performance and recovery, while also regulating skin temperature.
Other supposed benefits include increased blood return to the heart, improved clearance of metabolic byproducts of exercise, increased proprioception which means a person's perception of his body positioning , and enhanced comfort. But when these purported perks have been put to the test in actual scientific studies — not counting the trials conducted by clothing manufacturers — Stickford says the results have been mixed, and have primarily shown no real performance benefits of compression.
This is not to say that compression doesn't help muscles recover post-workout, which is another reason why athletes wear these items. You've probably experienced this with muddy MP3 files uploaded to YouTube. For example, compare this high-quality music track:. Lossy compression is suitable when a file contains more information than you need for your purposes. For instance, let's say you have a huge RAW image file. While you probably want to preserve that quality when printing the image onto a large banner, it's pointless to upload the RAW file to Facebook.
The picture contains so much data that isn't noticeable when viewed on social media sites. Compressing the image to a high-quality JPEG throws out some information, but the image looks almost the same to the naked eye. See our comparison of popular image formats for a deeper look at this. As we've mentioned, lossy compression is great for most forms of media.
Because of this, it's vital for companies like Spotify and Netflix that constantly transmit massive amounts of information. Reducing the file size as much as possible, while still preserving quality, makes their operation more efficient.
Can you imagine if every video YouTube was stored and transmitted in its original uncompressed format? But lossy compression doesn't work so well for files where all the information is crucial. For instance, using lossy compression on a text file or a spreadsheet would result in garbled output. You really can't throw anything out without severely harming the final product.
When saving in a lossy format, you can often set the level of quality. For instance, many image editors have a slider to choose the quality of a JPEG from Saving at something like 90 or 80 percent reduces the file size quite a bit, with little difference to the eye. But saving in poor quality or repeatedly saving the same file in a lossy format will degrade it. Below you can see an example of this click to see the larger images. The middle image is the result of saving this as a JPEG at 50 percent quality.
And the rightmost image shows the original image saved instead as a 10 percent quality JPEG. At a quick glance, the middle image doesn't look too bad. You can only notice the artifacts around the edges of the boxes if you zoom in.
Of course, the rightmost image immediately looks terrible. Lossless compression is a way of reducing file size so that you can perfectly reconstruct the original file. Contrary to lossy compression, it doesn't throw any information out. Instead, lossless compression essentially works by removing redundancy. Let's take a basic example to show what this means. Below is a stack of 10 bricks: two blue, five yellow, and three red. This stack is a simple way to illustrate those blocks, but there's another way to do so.
Instead of showing all 10 blocks, we can remove all but one of each color. Then, if we use numbers to show how many bricks of each color there were, we've represented the exact same bit of information using far fewer bricks.
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