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4.4 图像翻转和旋转Image Flipping and Rotation
用AspJpeg 1.2以上版本，你可以通过调用FilpH方法以及FlipV方法任意地水平/垂直翻转一张图片With AspJpeg 1.2+, you can invert an image horizontally and/or vertically by calling the methods FlipH and FlipV, respectively.
你也可以用RotateR方法以及RotateL方法任意地把一张图片顺时针旋转90度或者逆时针旋转90度.You can also rotate an image 90 degrees clockwise and counter-clockwise by calling the methods RotateR and RotateL, respectively.
4.5 调整图像压缩比Adjusting Image Compression
Jpeg图像格式采用了有损压缩方法，这意味着一张图片在保存为Jpeg过程中一些次要细节丢失了。损失程序可以用Jpeg.Quality属性来调节。这个属性认可一个从0到100范围的整型数值，0是损失率最高（因此，质量最低），100是损失率最低，质量最高。The JPEG format uses "lossy" compression methods. This means that some minor details of an image saved as a JPEG are lost during compression. The degree of loss can be adjusted via the Jpeg.Quality property. This property accepts an integer in the range 0 to 100, with 0 being the highest degree of loss (and hence, the lowest quality) and 100 being the lowest degree of loss and highest quality.
损失率越低，生成的文件体积越大。属性值Jpeg.Quality默认值被设置为80，它提供了一个接近最佳的图像质量和文件体积组合。The lower the loss, the larger the resultant file size. The property Jpeg.Quality is set to 80 by default which provides a close-to-optimal combination of quality and file size.
4.6 灰度转换Grayscale Conversion
从1.4版开始，AspJpeg通过Grayscale方法可以把一张彩****片转换成灰度，这个方法Starting with version 1.4, AspJpeg is capable of converting a color image to grayscale via the Grayscale method. This method expects a Method argument which specifies a formula to perform the color-to-B&W conversion. The valid values are 0, 1, and 2. The value of 1 is the recommended method for most applications.
The Grayscale method sets the three color components (R, G, B) of each pixel to the same value L using the following formulas
| Method | Formula |
| 0 | L = 0.3333 R + 0.3333 G + 0.3333 B |
| 1 | L = 0.2990 R + 0.5870 G + 0.1140 B |
| 2 | L = 0.2125 R + 0.7154 G + 0.0721 B |
The effect of the Method argument is demonstrated by the chart below:
| Method | Effect |
| Original Image |  |
| 0 |  |
| 1 |  |
| 2 |  |
方法0的效果在photoshop中称为“去色”（图像->调整->去色）The effect of Method 0 is what Photoshop calls desaturation (Image/Adjust/Desaturate), while Method 1 is similar to Photoshop's conversion from RGB to grayscale (Image/Mode/Grayscale).
注意Grayscale是一个方法，不是一个属性，所以“=”号是不能够用的。必须写成以下样式：Note that Grayscale is a method, not a property, so the '=' sign should not be used:
Jpeg.Grayscale 1
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