如何通过gm identify -verbose获取RGB通道的标准差数值

我需要从gm identify -verbose的输出中获取Red、Green、Blue通道对应的Standard Deviation（标准差）数值，但该值无法通过-format选项直接指定，请问如何通过命令行实现？

纯命令行解决方案 #

可以通过awk结合gm identify过滤提取目标数值，命令如下：

gm identify -verbose 你的图片路径.jpg | awk '/Channel Statistics:/ {flag=1; next} /^  [A-Z]/ {if (flag) {channel=$1; flag=0}} /Standard Deviation:/ {print channel ": " $3}'

执行后会输出类似结果：

Red: 45.92
Green: 55.13
Blue: 55.71

PHP实现方案 #

如果需要在PHP中处理，可以通过执行shell命令结合正则提取数值：

$file = '你的图片路径.jpg';
// 过滤出包含Standard Deviation的行
$raw = `gm identify -verbose {$file} | grep -E '^ +(Standard Deviation): *[^b]*$'`;
// 正则提取数值部分
preg_match_all("/(?<=Standard Deviation:)(?: +)([\d\.]+)/", $raw, $matches);
// 按Red、Green、Blue顺序整理结果
$stdDeviations = [
    'Red' => $matches[1][0],
    'Green' => $matches[1][1],
    'Blue' => $matches[1][2]
];

// 输出结果
print_r($stdDeviations);

参考输出示例 #

gm identify -verbose的典型输出片段（我们需要提取Channel Statistics下对应通道的标准差）：

Image: /.../.../img.jpg
  Format: JPEG (Joint Photographic Experts Group JFIF format)
  Geometry: 1064x1600
  Class: DirectClass
  Type: true color
  Depth: 8 bits-per-pixel component
  Channel Depths:
    Red:      8 bits
    Green:    8 bits
    Blue:     8 bits
  Channel Statistics:
    Red:
      Minimum:                     0.00 (0.0000)
      Maximum:                   255.00 (1.0000)
      Mean:                      132.32 (0.5189)
      Standard Deviation:         45.92 (0.1801)
    Green:
      Minimum:                     0.00 (0.0000)
      Maximum:                   255.00 (1.0000)
      Mean:                      104.17 (0.4085)
      Standard Deviation:         55.13 (0.2162)
    Blue:
      Minimum:                     0.00 (0.0000)
      Maximum:                   255.00 (1.0000)
      Mean:                      103.61 (0.4063)
      Standard Deviation:         55.71 (0.2185)
  Filesize: 452.0Ki
  Interlace: No
  Orientation: Unknown
  Background Color: white
  Border Color: #DFDFDF
  Matte Color: #BDBDBD
  Page geometry: 1064x1600+0+0
  Compose: Over
  Dispose: Undefined
  Iterations: 0
  Compression: JPEG
  JPEG-Quality: 95
  JPEG-Colorspace: 2
  JPEG-Colorspace-Name: RGB
  JPEG-Sampling-factors: 2x2,1x1,1x1
  Signature: 136912e901ae9314fd683868418cae1f5d838c6891ddd8c13ce28057fb39365a
  Tainted: False
  User Time: 0.010u
  Elapsed Time: 0m:0.014459s
  Pixels Per Second: 112.3Mi

内容的提问来源于stack exchange，提问作者yarns