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.