In-depth Analysis of Image Compression Technology

I. The Importance of Image Compression

With the popularization of high-definition images, the size of image files has increased dramatically. A picture taken by a mobile phone may be several megabytes in size, and a RAW format file taken by a professional camera may reach dozens of megabytes. These large amounts of image data piling up on hard drives, servers, or cloud storage will quickly occupy a huge amount of storage space. If the images are reasonably compressed at this time, the size of the image files can be reduced by 50% - 90%. For enterprises and individuals storing massive amounts of data, this can save a lot of resources and costs.

II. The Basic Principles of Image Compression

1. Principle of Lossless Compression

The core of lossless compression is to reduce the file size without losing any original image information. It mainly takes advantage of statistical redundancy in the data. For example, in an image containing a large area of a single color, lossless compression will identify these repeated areas and simplify them through a specific coding method.

2. Principle of Lossy Compression

Lossy compression is based on the characteristics of the human visual system. It achieves a significant reduction in file size by discarding some information that is not easily noticeable to the human eye. Taking the widely used JPEG format as an example, its core is the Discrete Cosine Transform (DCT). First, the picture is divided into 8x8 pixel blocks, and each pixel block is subjected to DCT transformation to convert the pixel information in the spatial domain to the frequency domain.

III. Common Compression Formats

Next, we will mainly introduce common image compression formats. What are the differences in their processing methods?

1. JPEG: Currently, it is the most widely used lossy compression image format on the Internet. As mentioned above, it achieves efficient compression through DCT transformation. At the same time, JPEG achieves a good balance between image quality and file size, and is suitable for photos and images with rich colors and more details.

2. PNG: It is a lossless compression image format, suitable for images with large areas of the same color, such as icons, web elements, etc. Different from JPEG, PNG uses the L777 series of algorithms and entropy coding for compression. It supports a transparent background and has high image quality. However, due to its lossless compression characteristics, the file is relatively large.

3. WebP: It is a modern image format developed by Google, supporting both lossy and lossless compression. Compared with JPEG and PNG, WebP has higher compression efficiency.

IV. Differences in Different Compression Technologies

1. Differences in Processing Flow

When processing JPEG images, first, the compression quality parameter (usually 0 - 100) needs to be set. The lower the parameter, the higher the compression rate and the greater the loss. During the saving process, the software will perform steps such as DCT transformation, quantization, and entropy coding, and each save will re - perform quantization, resulting in cumulative loss.

When processing PNG images, the quality parameter needs to be set, and the compression process is automatically completed by the algorithm. The save operation performs lossless coding, and the pixel information will not change no matter how many times it is saved.

2. Differences in Editing Characteristics

JPEG is not suitable for repeated editing because each save operation after editing will introduce new quality losses. If you need to modify a JPEG image multiple times, it is recommended to first convert it to a lossless format such as TIFF for editing, and then export it as JPEG after completion.

PNG is an ideal choice for editing, especially for images that need to be modified multiple times. Whether it is resizing, adding elements, or changing colors, it will not affect the original quality of the image.