node平台截取图片模块——jimp

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前几天介绍了一个简单的截图模块——iamges，虽然简单，但是功能还是有很多局限的地方。

jimp的优势：1.简单，2.支持回调方式和ES6（promise）语法也可以链式调用 3. 丰富的api 4.无需安装任何程序（gm和canvas都需要）

jimp的回调用法如下：

var Jimp = require("jimp"); Jimp.read("lenna.png", function (err, lenna) {
if (err) throw err;
lenna.resize(256, 256)
.quality(60)
.greyscale()
.write("lena-small-bw.jpg");
});

promise用法：

var Jimp = require("jimp"); Jimp.read("lenna.png").then(function (lenna) {
lenna.resize(256, 256)
.quality(60)
.greyscale()
.write("lena-small-bw.jpg");
}).catch(function (err) {
console.error(err);
});

因为代码是运行在node平台，个人强烈建议使用promise的写法。

更多的用法可以参考github：https://github.com/oliver-moran/jimp，我把一些api复制下来

/* Resize */
image.contain( w, h[, mode] ); // scale the image to the given width and height, some parts of the image may be letter boxed
image.cover( w, h[, mode] ); // scale the image to the given width and height, some parts of the image may be clipped
image.resize( w, h[, mode] ); // resize the image. Jimp.AUTO can be passed as one of the values.
image.scale( f[, mode] ); // scale the image by the factor f
image.scaleToFit( w, h[, mode] ); // scale the image to the largest size that fits inside the given width and height// An optional resize mode can be passed with all resize methods./* Crop */
image.autocrop(); // automatically crop same-color borders from image (if any)
image.crop( x, y, w, h ); // crop to the given region/* Composing */
image.blit( src, x, y[, srcx, srcy, srcw, srch] );
// blit the image with another Jimp image at x, y, optionally cropped.
image.composite( src, x, y ); // composites another Jimp image over this iamge at x, y
image.mask( src, x, y ); // masks the image with another Jimp image at x, y using average pixel value image.rotate) and when writing formats that don't support alpha channels/* Flip and rotate */
image.flip( horz, vert ); // flip the image horizontally or vertically
image.mirror( horz, vert ); // an alias for flip
image.rotate( deg[, mode] ); // rotate the image clockwise by a number of degrees. Optionally, a resize mode can be passed. If `false` is passed as the second parameter, the image width and height will not be resized.// JPEG images with EXIF orientation data will be automatically re-orientated as appropriate./* Colour */
image.brightness( val ); // adjust the brighness by a value -1 to +1
image.contrast( val ); // adjust the contrast by a value -1 to +1
image.dither565(); // ordered dithering of the image and reduce color space to 16-bits (RGB565)
image.greyscale(); // remove colour from the image
image.invert(); // invert the image colours
image.normalize(); // normalize the channels in an image/* Alpha channel */
image.fade( f ); // an alternative to opacity, fades the image by a factor 0 - 1. 0 will haven no effect. 1 will turn the image
image.opacity( f ); // multiply the alpha channel by each pixel by the factor f, 0 - 1
image.opaque(); // set the alpha channel on every pixel to fully opaque
image.background( hex ); // set the default new pixel colour (e.g. 0xFFFFFFFF or 0x00000000) for by some operations (e.g. image.contain and /* Blurs */
image.gaussian( r ); // Gaussian blur the image by r pixels (VERY slow)
image.blur( r ); // fast blur the image by r pixels/* Effects */
image.posterize( n ); // apply a posterization effect with n level
image.sepia(); // apply a sepia wash to the image