JPEG压缩

[delphi1234567]

如何对JPEG文件进行压缩,不改变图像的长度及宽度,只调整其压缩率.
压缩后,生成的文件在 1024K 以内,但最接近 1024K. (1024K只是一个例子,可以更小,比如:100K等,目的是让用户自己设定)

目前100点,解决后另付300点.

[CDSoftwareWj]

不可能吧，JPEG格式，本身就是压缩了的（JPEG无损压缩格式除外）不信你可以用RAR压压看少了多少？？

[SeaWave]

楼上大概未理解楼主的意思，楼主的意思是想重新调整JPEG的压缩率。

用TJpegImage吧，调整CompressionQuality属性的值，再调用Compress方法就可以改变其压缩率，当然，图像质量与压缩率是成反比的。

[zousoft]

同意楼上!
来晚了, 给你贴两断help吧. hehe

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Delphi syntax:

procedure Compress;

C++ syntax:

void __fastcall Compress(void);

Description

Call Compress to compress for optimization, such as before streaming out when assigning a bitmap to a jpeg. Changing properties like CompressionQuality does not force compression. To force compression, call Compress.



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Indicates 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.

[zousoft]

补充: TJPEGQualityRange是1..100

[miky]

用TJpegImage吧，调整CompressionQuality属性的值，再调用Compress方法就可以改变其压缩率，当然，图像质量与压缩率是成反比的。

那么CompressionQuality设为多少合适呢？

[ly_liuyang]

这就说不准了
但一般是50到70的

[eliphe]

首先要user jpeg;

用TJpegImage吧，调整CompressionQuality属性的值，再调用Compress方法就可以改变其压缩率，当然，图像质量与压缩率是成反比的。

[yjy1001]

最一般的是75
但最低也要25 否则失真太多

请楼主自己看 <Visual C++ 实现MPEG/JPEG编解码技术> 一书里面有详细的源码 这里不帖了