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19 Graphics creation (1 questions)
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The Discrete Cosine Transform (DCT) is a mathematical technique used in JPEG image compression to transform the image data from the spatial domain (pixel values) to the frequency domain.
How DCT works in JPEG:
- Block Division: The image is divided into 8x8 pixel blocks.
- DCT Transformation: The DCT is applied to each 8x8 block. This transforms the spatial representation of the pixels into a representation of different frequency components. Lower frequencies represent gradual changes in the image, while higher frequencies represent sharp changes (e.g., edges).
- Quantization: The DCT coefficients are quantized, which means they are rounded to the nearest integer. This is where the most significant data loss occurs. Higher frequency coefficients are often quantized more aggressively, leading to greater compression but potentially more noticeable artifacts.
- Entropy Coding: The quantized DCT coefficients are then further compressed using entropy coding techniques like Huffman coding or arithmetic coding, which exploit statistical redundancies in the data.
By concentrating the image energy into a few low-frequency DCT coefficients and discarding or coarsely quantizing the high-frequency coefficients, DCT enables significant compression while minimizing the perceptual impact on image quality. The amount of quantization determines the compression ratio and the level of image degradation.