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。。
回复讨论(解决方案)
php.ini里有upload_max_filesize = 128M 可以设置大小吧！而且在html页面也可以设置中的value来限制大小
无压缩图片大概一个像素3字节（RGB），jpg约为1/6大小，当然可以更小，但失真更大就是了
可以重采样使用更大压缩比减少字节数，但一般服务器不做这事，因为大量操作很吃资源的
php.ini里有upload_max_filesize = 128M 可以设置大小吧！而且在html页面也可以设置中的value来限制大小
不是不让上传，而是把上传的图片改小
gd库生成缩略图就是了
gd库生成缩略图就是了
是不是只能指定尺寸，但不能保证一定在200K以下？
可以的。尺寸会影响大小。
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...
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
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
平时用相机照出来的图片，在电脑里用查看图片的软件打开看到应该不是图片的实际尺寸？
如果用 100个像素表示头发，那图片本身尺寸是不是很大？
其实我想问的就是像素和图片尺寸的联系。
如果用 100个像素表示头发，那图片本身尺寸是不是很大？
那也不一定，如果那个图片中就只有一根头发，那不也就只有100个像素吗？
建议你先复习一下 分辨率 的知识
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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