compression ratio(Compression rate), descriptionCompressed fileThe effect name is the ratio of the size of the compressed file to the size before compression. For example, if a 100m file is compressed to 90m, the compression ratio is 90/100 * 100%=90%. The smaller the compression ratio, the better, but the smaller the compression, the longer the decompression time.[1]
Audio compression technologyThis refers to the application of the appropriateDigital signal processing technology, reduce (compress) its bit rate without losing useful information or the induced loss is negligible, which is also called compression coding.[2]
It must have a corresponding inverse transform, called decompression or decoding.The audio signal may introduce a lot of noise and cause some distortion after passing through the encoding and decoding systems.[2]
Audio mode
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In the field of audio compression, there are two compression methods, lossy compression and lossless compression.[2]
Lossy compression
The common MP3, WMA and OGG are called lossy compression. Just as the name implies, lossy compression is to reduce the audio sampling frequency and bit rate, and the output audio file will be smaller than the original file.[2]
lossless compression
Lossless compression can compress the capacity space of the audio file to a smaller size on the premise that 100% of the source file's data is saved. After the compressed audio file is restored, it can achieve the same size and code rate as the source file.[2]
Image Introduction
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If the image is not compressed, the amount of image data will be large, thus reducing the amount of storage.Therefore, image compression formats such asJPEG format。In the same case, the amount of photo data with low compression ratio is smaller.With a storage device of the same capacity, you can store more photos.However, in a certain range, the lower the compression ratio (that is, the higher the compression efficiency), the lower the photo quality.[3]
Image mode
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In terms of image quality and occupation of memory card orComputer hard diskIn terms of storage space, the selection of file format plays a very important role.It is important to note that some formats automatically compress files when saving images[3]
There are two forms of image compression: lossy compression and lossless compression.The image information compressed in lossy compression format is usually lost, leading to the decline of image quality. The smaller the file is compressed, the more information is lost.[3]
Storage format
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JPEG
This mode is the file mode most frequently used by photographers.It uses a distorted image compression method to compress the image in a very small storage space, which is a lossy compression mode, and will lose some image quality in the compression process.[3]
TIFF
TIFF mode is the most common compression format. Although most software supports this file format, only advanced cameras support this file format.The photos scanned by the scanner are also recorded in this format.It can maintain the color and level of the original image, but it takes a lot of space.[3]
RAW
In order to ensure the quality of the final image, many professional cameras can save the image as a RAW grid, retaining enough image information.Its data is the original file that has not been processed by the camera.[3]
GIF
The extension is GIF.In the process of compression, the pixel data of the image will not be lost, but what is lost is the color of the image.GIF format can only store 256 colors at most, so it is usually used to display simple graphics and fonts.[3]
Best results
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When saving photos in JPEG format, it is best to select the lowest compression rate.When using image processing software such as Adobe Photoshop to save, the compression ratio of JPEG files available is 1-12. The lower the value, the smaller the image file, and the lower the compression ratio, the greater the impact on photo quality.For better picture quality, you'd better choose a higher value of 10-12 to save the picture.But when 12 is selected.The size of the image file will exceed 5MB, and the image file is too large, which is inconvenient to save and transfer.useDigital SLR cameraPhotos taken and stored with the highest quality of JPEG are saved in JPEG format in Photoshop. Considering the image size, most of them choose the compression rate between 11-12.[4]
Compression software
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JPEG Optimizer
JPEG Optimizer is a tool software that can compress JPEG format pictures according to the specified compression ratio. It uses Magic Compress technology to compress JPEG graphic files by 50% without loss of image quality. The compression ratio can be customized to show the compressed pictures in real time. Compared with the difference, the effect is relatively good.All this can be achieved by adjusting the compression ratio through the adjusting rod.[5]
The JPEG Wizard
The JPEG Wizard can compress the picture to the maximum extent without affecting the image quality. At the same time, it supports local compression, cutting, and rotation of the picture, and adjusts the contrast, brightness, and chroma of the picture.In addition, The JPEGWizard also has a strong batch processing function to avoid repetitive operations.[5]
7-Zip
7-Zip is a compression software that boasts the highest compression ratio today. It not only supports the unique 7z file format, but also supports a variety of other compressed file formats, including ZP, RAR, CAB, GZIP, BZP2 and TAR.The compression ratio of this software is 30%~50% higher than that of ordinary ZIP files.Therefore, it can compress Winzip compressed files by 2%~10%.[6]
