Howtosignalprocessing
- What is the purpose of zig zag scanning?
- Why zig zag scanning was used instead of simply scanning the DCT coefficients row by row from top to bottom?
- Why DCT is used in image compression?
- How DCT is used for image compression with JPEG standard?
What is the purpose of zig zag scanning?
What is the purpose of the Zig-zag Scan: to group low frequency coefficients in top of vector.
Why zig zag scanning was used instead of simply scanning the DCT coefficients row by row from top to bottom?
Another reason why the zigzag scan is used is related to JPEG quantization. As @Mahdi noted, zigzag scanning will order the DCT coefficients so that ones with higher energy appear first, then lower after.
Why DCT is used in image compression?
The DCT has the property that, for a typical image, most of the visually significant information about the image is concentrated in just a few coefficients of the DCT. For this reason, the DCT is often used in image compression applications.
How DCT is used for image compression with JPEG standard?
The DCT can be used to convert the signal (spatial information) into numeric data ("frequency" or "spectral" information) so that the image's information exists in a quantitative form that can be manipulated for compression. The signal for a graphical image can be thought of as a three-dimensional signal.
