I am writing decompressor for jpeg files I know that it's very complex process but anyway I have read this tutorial http://www.impulseadventure.com/photo/jpeg-huffman-coding.html it was very useful until I reached this
期望图像内容是3个成分(Y,Cb,Cr).在每个组件内,序列始终是一个DC值,后跟63个AC值.
那么DC和AC的含义是什么？
Mar*_*ler 16
简单地说,离散余弦变换(DCT)的第一个元素是DC或直流项,它是像素值的平均值.其余元素,AC或交流电项,与平均值无关.因此,如果您为所有像素值添加相同的数字,则只有DCT的DC项会发生变化.AC条款将保持不变.
这类似于用电容器滤除信号的直流分量,只允许交流分量通过.