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PHP 处置图片

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Jun 13, 2016 am 11:21 AM

100200kjpg

PHP 处理图片

有个上传图片的功能
如何每次把上传的图片大小控制在200K以下？
只能更改图片的尺寸吗？
其实图片的像素和尺寸和清晰度等都有什么联系。。

------解决方案--------------------
可以的。尺寸会影响大小。
------解决方案--------------------
控制一下压缩比例，因为有的图片像素太大的话，比例缩略到指定比例也不一定会小于200k，所以要控制你最大上传图片的大小缩略到200k的最佳比例...
------解决方案--------------------
从目前流行的图片采集设备上看，200K 只不过是一张普通邮票
清晰度是指表示已知大小的目标所耗费的像素素，当然是越多越清晰

比如，头发的直径约在70～100μm之间
你用一个像素表示，那么只是一条细线
你用100个像素表示的话，你将能看到发身上的鳞片
------解决方案--------------------
像素和图片尺寸的关系是单元和总体的关系
像素和图片文件尺寸（字节数）的关系我在#2说了
一幅1024x500像素的无损全彩（24bit）图片就是1500k再加文件头，jpg（非jpg2000）就大概是无损的1/6约250k
说“大概”，“约”是因为jpg有多级压缩率，每像素的颜色值也有影响，故字节数不定
同样像素的“万花筒”和纯色图片，均使用24bit采样，两者无损图片格式的字节数一样，但jpg格式后者字节数就小很多

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