composite命令可以非常方便的合并兩張圖片
因此用來進行圖像加水印、批量增加邊框等常用的變換
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最簡單的用法為：
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composite -gravity north src.jpg coverback.jpg des.jpg
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其中src.jpg為前景圖片
coverback.jpg為背景圖片。
des.jpg為疊加后的結果
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-gravity north 指疊加位置為垂直據頂部、水平居中（正北方向）
如果要求在正中間，參數為center
如果要求在右下角，參數為southeast
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composite還提供更靈活的定位，可以使用 -geometry 配置
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具體的composite參數表見下表
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| ? -affine?matrix | affine transform matrix |
| -alpha | on, activate, off, deactivate, set, opaque, copy", transparent, extract, background, or shape the alpha channel |
| -authenticate?value | decrypt image with this password |
| -blend?geometry | blend images |
| -blue-primary?point | chromaticity blue primary point |
| -border?geometry | surround image with a border of color |
| -bordercolor?color | border color |
| -channel?type | apply option to select image channels |
| -colors?value | preferred number of colors in the image |
| -colorspace?type | set image colorspace |
| -comment?string | annotate image with comment |
| -compose?operator | set image composite operator |
| -compress?type | image compression type |
| -debug?events | display copious debugging information |
| -decipher?filename | convert cipher pixels to plain |
| -define?format:option | define one or more image format options |
| -density?geometry | horizontal and vertical density of the image |
| -depth?value | image depth |
| -displace?geometry | shift image pixels defined by a displacement map |
| -dissolve?value | dissolve the two images a given percent |
| -dither?method | apply error diffusion to image |
| -encipher?filename | convert plain pixels to cipher pixels |
| -encoding?type | text encoding type |
| -endian?type | endianness (MSB or LSB) of the image |
| -extract?geometry | extract area from image |
| -filter?type | use this filter when resizing an image |
| -font?name | render text with this font |
| -geometry?geometry | preferred size or location of the image |
| -gravity?type | horizontal and vertical text placement |
| -green-primary?point | chromaticity green primary point |
| -help | print program options |
| -identify | identify the format and characteristics of the image |
| -interlace?type | type of image interlacing scheme |
| -interpolate?method | pixel color interpolation method |
| -label?string | assign a label to an image |
| -level?value | adjust the level of image contrast |
| -limit?type value | pixel cache resource limit |
| -log?format | format of debugging information |
| -monitor | monitor progress |
| -monochrome | transform image to black and white |
| -negate | replace each pixel with its complementary color |
| -page?geometry | size and location of an image canvas (setting) |
| -pointsize?value | font point size |
| -profile?filename | add, delete, or apply an image profile |
| -quality?value | JPEG/MIFF/PNG compression level |
| -quantize?colorspace | reduce image colors in this colorspace |
| -quiet | suppress all warning messages |
| -red-primary?point | chromaticity red primary point |
| -regard-warnings | pay attention to warning messages. |
| -respect-parentheses | settings remain in effect until parenthesis boundary. |
| -rotate?degrees | apply Paeth rotation to the image |
| -sampling-factorgeometry | horizontal and vertical sampling factor |
| -scene?value | image scene number |
| -seed?value | seed a new sequence of pseudo-random numbers |
| -set?attribute value | set an image attribute |
| -sharpen?geometry | sharpen the image |
| -shave?geometry | shave pixels from the image edges |
| -size?geometry | width and height of image |
| -stegano?offset | hide watermark within an image |
| -stereo?geometry | combine two image to create a stereo anaglyph |
| -strip | strip image of all profiles and comments |
| -swap?indexes | swap two images in the image sequence |
| -synchronize | synchronize image to storage device |
| -taint | mark the image as modified |
| -thumbnail?geometry | create a thumbnail of the image |
| -tile | repeat composite operation across and down image |
| -transform | affine transform image |
| -transparent-colorcolor | transparent color |
| -treedepth?value | color tree depth |
| -type?type | image type |
| -units?type | the units of image resolution |
| -unsharp?geometry | sharpen the image |
| -verbose | print detailed information about the image |
| -version | print version information |
| -virtual-pixel?method | access method for pixels outside the boundaries of the image |
| -watermarkgeometry | percent brightness and saturation of a watermark |
| -white-point?point | chromaticity white point |
| -white-thresholdvalue | force all pixels above the threshold into white |
| -write?filename | write images to this file |
