由于存储介质、传输速度等因素的限制，通常需要将大的图像文件变小。Photoshop 中主要有两种图像变小的 方法：一种是在存储文件时选择更低品质的JPEG 压缩格式；一种是在重定图像像素的情况下降低图像的分辨率。多数PS 用 户不清楚这两种方法的区别与联系，以及针对实际应用如何进行选择。国内外也缺少对此方面的研究。本文从原理、对图像 的影响等方面对这两种图像变小方法进行了对比分析，并引用了三个现实中的实例，有针对性地论述了如何选用两种图像变 小方法，对PS 用户有现实的指导意义。

For the limitation of storage medium and transmission speed, we usually need to reduce image file size. There are two methods in Photoshop: one is to choose a lower quality compression format when storing files; the other is to reduce the number of pixels in resample image case. Most PS users don't know the difference and connection between the two methods, and how to choose according to the practical application. Also, there is lack of research on this area at home and abroad. In this paper, these two methods are analyzed in theory and effect and it cites three real examples to discuss how to choose the method according to the practical application. It has the reality guiding significance for PS users.