JPEG Image Compression Technique

JPEG is a commonly used technique for lossy compression for digital images, particularly for those images produced by digital photography. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality.

The JPEG Image Compression Technique consists of Five Functional Stages.

An RGB to YCC color space conversion,
A spatial subsampling of the chrominance channels in YCC space
The transformation of a blocked representation of the YCC spatial
image data to a frequency domain representation using the discrete cosine transform,
A quantization of the blocked frequency domain data according to a user-defined quality factor, and finally
The coding of the frequency domain data, for storage, using Huffman coding.

The human visual system relies more on spatial content and acuity than it does on colors for interpretation. For this reason, a color photograph, represented by a red, green, and blue image, is transformed to different color space that attempts to isolate these two components of the image content; namely the YCC or luminance/Chrominance-red/chrominance blue color space. This color space transformation is performed on a pixel-by-pixel basis with the digital counts being converted according to the following rules:

JPEG Compression Step:

jpeg compressed image data > decoding > de-quantization > inverse DCT > up-sampling > color transform> raw image data > color transform > down sampling > forward DCT > quantization > en coding. PNG Compression: Portable Network Graphics

How Does it Work?

When you upload a PNG (Portable Network Graphics) file, similar colors in your image are combined. This technique is called “quantization”. By reducing the number of colors, 24-bit PNG files can be converted to much smaller 8-bit indexed color images. All additional metadata is stripped too. The result: better PNG files with 100% support for transparency

Is It Supported Everywhere?

The files produced by TinyPNG are displayed correctly on all modern browsers including mobile devices. Still, need to support Internet Explorer 6? It usually ignores PNG transparency and displays a solid background color. With TinyPNG the background becomes transparent again. Binary transparency without any workarounds!

TIFF Compression

The TIFF image format is regarded as the gold standard for long-term storage of static image data. It is flexible, widely supported, and rich in its treatment of both image data and metadata. Its historical disadvantage has been its massive file sizes; this can, however, be mitigated by the use of compression, support for which is built into the format and described in the TIFF compression tag for each file.

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