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Your Website Page Speed is a major ranking factor. Website visitors are expecting exceedingly fast web experiences in this mobile age of the internet. It’s crucial to get aggressive and take control of your image sizes to deliver a faster loading website to your visitors. Below I’ll explain the image compression types and the methods for compressing them. I’ll also list 10 tools you can use to compress images.
The objective of Image Compression is to decrease irrelevant & redundant data in the image in order to be able to store and transmit data in an efficient format.
Image Compression is either Lossy or Lossless
- Lossy works by discarding information from the original file. It’s especially suitable for natural images such as photographs in applications where minor (sometimes imperceptible) loss of fidelity is acceptable to achieve a substantial reduction in bit rate.
- Lossless retains all the original data. It’s often used for medical imaging, technical drawings or comics (though, the file size tends to be bigger). There’s a variety of image compression algorithms that take different approaches to reducing file size, and the tools listed below utilize a number of those to minimize the size of your images.
Method for Compressing
Methods for Lossy compression:
- Reducing the color space to the most common colors in the image. The selected colors are specified in the color palette in the header of the compressed image. Each pixel just references the index of a color in the color palette, this method can be combined with dithering to avoid posterization.
- Chroma subsampling. This takes advantage of the fact that the human eye perceives spatial changes of brightness more sharply than those of color, by averaging or dropping some of the chrominance information in the image.
- Transform coding. This is the most commonly used method. In particular, a Fourier-related transform such as the Discrete Cosine Transform (DCT) is widely used: N. Ahmed, T. Natarajan and K.R.Rao, “Discrete Cosine Transform,” IEEE Trans. Computers, 90-93, Jan. 1974. The DCT is sometimes referred to as “DCT-II” in the context of a family of discrete cosine transforms; e.g., see discrete cosine transform. The more recently developed wavelet transform is also used extensively, followed by quantization and entropy coding.
- Fractal compression.
Methods for Lossless image compression are:
- Run-length encoding – used as default method in PCX and as one of possible in BMP, TGA, TIFF
- Area image compression
- DPCM and Predictive Coding
- Entropy encoding
- Adaptive dictionary algorithms such as LZW – used in GIF and TIFF
- Deflation – used in PNG, MNG, and TIFF
- Chain codes
Below is a video from MIT Professor Gilbert Strang teaching Image Compression in 1999. Still applies in 2016.
Whether it’s JPEG, PNG, GIF or SVG, these tools have you covered with this selection of free, premium, online and desktop-based image compressors. All of them will help you compress your website’s images, save bandwidth and improve your site’s performance.
If you use WordPress for your website CMS then you can simply download one of the following pluggins.
ShortPixel Image Optimizer
Optimus – WordPress Image Optimizer
Compress JPEG & PNG images
Imagify Image Optimizer
RICG Responsive Images
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