我從版上學到可以利用Assign的方法將jpeg解為bitmap檔案，小弟也試著反向將bitmap再壓回jpeg檔案，但是檔案就變成約原來的4倍大！ 不知道究竟是為什麼呢？難道是壓縮率變低了嗎？ 先謝謝大家！

Extracted from help: CompressionQuality property (TJPEGImage) ndicates the trade-off ratio between the image quality and the file size. Delphi syntax: property CompressionQuality: TJPEGQualityRange; C syntax: __property TJPEGQualityRange CompressionQuality = { read=FQuality, write=FQuality, nodefault}; Description Use CompressionQuality to set the compression quality of the JPEG image when writing out a jpeg image. Higher compression results in a poorer picture quality, but a smaller file size. This property is not used for reading in files. TJPEGQualityRange is the type of the CompressionQuality property. The higher the TJPEGQualityRange value (up to a maximum of 100), the better the image quality, but the larger the file size. The lower the TJPEGQualityRange value (to a minimum of 1), the smaller the resulting file size, but at the expense of picture quality.

多謝william!