使用mogrify进行从jpg到png的无损转换

Question

我试图使用qazxsw poi将qazxsw poi图像无损地转换为qazxsw poi图像。要获得此结果，我正在使用此命令：

jpg

然而，检查两个图像是否相同的测试失败。要执行测试，我使用这个png脚本：

mogrify

如果两个图像相同，则此脚本的执行显示黑色矩形。

我尝试使用mogrify -format png test.jpeg 进行转换，它的工作原理。这是我用python获得结果的

import cv2

jpg_image = cv2.imread("test.jpeg")
png_image = cv2.imread("test.png")

diff = jpg_image - png_image

cv2.imshow("diff", diff)
cv2.waitKey(0)
cv2.closeAllWindows()

脚本：

opencv

正如下面的评论中所建议的，我还在python和opencv生成的

import cv2

jpg_image = cv2.imread("/home/roberto/Downloads/index.jpeg")
cv2.imwrite("/home/roberto/Downloads/index.png", jpg_image)

文件上运行了identify -verbose命令。这些是输出：

png

mogrify

opencv：

mogrify

谁能解释我第一种和第二种方法之间的区别（

Image: index.png24
  Format: PNG (Portable Network Graphics)
  Mime type: image/png
  Class: DirectClass
  Geometry: 276x183+0+0
  Units: Undefined
  Type: TrueColor
  Endianess: Undefined
  Colorspace: sRGB
  Depth: 8-bit
  Channel depth:
    red: 8-bit
    green: 8-bit
    blue: 8-bit
  Channel statistics:
    Pixels: 50508
    Red:
      min: 0 (0)
      max: 153 (0.6)
      mean: 19.2985 (0.0756804)
      standard deviation: 16.1262 (0.06324)
      kurtosis: 4.912
      skewness: 1.86378
      entropy: 0.805148
    Green:
      min: 0 (0)
      max: 176 (0.690196)
      mean: 64.9359 (0.254651)
      standard deviation: 45.101 (0.176867)
      kurtosis: -0.895497
      skewness: 0.554883
      entropy: 0.968001
    Blue:
      min: 0 (0)
      max: 255 (1)
      mean: 144.46 (0.566511)
      standard deviation: 50.6283 (0.198542)
      kurtosis: -0.289594
      skewness: -0.566585
      entropy: 0.950031
  Image statistics:
    Overall:
      min: 0 (0)
      max: 255 (1)
      mean: 76.2316 (0.298948)
      standard deviation: 40.2384 (0.157798)
      kurtosis: 11.4068
      skewness: 2.70212
      entropy: 0.907726
  Rendering intent: Perceptual
  Gamma: 0.45455
  Chromaticity:
    red primary: (0.64,0.33)
    green primary: (0.3,0.6)
    blue primary: (0.15,0.06)
    white point: (0.3127,0.329)
  Background color: white
  Border color: srgb(223,223,223)
  Matte color: grey74
  Transparent color: black
  Interlace: None
  Intensity: Undefined
  Compose: Over
  Page geometry: 276x183+0+0
  Dispose: Undefined
  Iterations: 0
  Compression: Zip
  Orientation: Undefined
  Properties:
    date:create: 2019-03-21T09:51:42+01:00
    date:modify: 2019-03-21T09:51:42+01:00
    png:bKGD: chunk was found (see Background color, above)
    png:cHRM: chunk was found (see Chromaticity, above)
    png:gAMA: gamma=0.45454544 (See Gamma, above)
    png:IHDR.bit-depth-orig: 8
    png:IHDR.bit_depth: 8
    png:IHDR.color-type-orig: 2
    png:IHDR.color_type: 2 (Truecolor)
    png:IHDR.interlace_method: 0 (Not interlaced)
    png:IHDR.width,height: 276, 183
    png:sRGB: intent=0 (Perceptual Intent)
    png:text: 2 tEXt/zTXt/iTXt chunks were found
    signature: 1bdb735da64a7036eb46f2d257997fbd10044ddc633c2aea5703f1887614709c
  Artifacts:
    filename: index-mogrify.png
    verbose: true
  Tainted: False
  Filesize: 79.9KB
  Number pixels: 50.5K
  User time: 0.000u
  Elapsed time: 0:01.000
  Version: ImageMagick 6.9.7-4 Q16 x86_64 20170114 http://www.imagemagick.org

vs opencv）？

Answer 1

两幅图像之间的差异可以忽略不计。我在左边显示了ImageMagick，在右边显示了一个OpenCV。

Image: index-opencv.png
  Format: PNG (Portable Network Graphics)
  Mime type: image/png
  Class: DirectClass
  Geometry: 276x183+0+0
  Units: Undefined
  Type: TrueColor
  Endianess: Undefined
  Colorspace: sRGB
  Depth: 8-bit
  Channel depth:
    red: 8-bit
    green: 8-bit
    blue: 8-bit
  Channel statistics:
    Pixels: 50508
    Red:
      min: 0 (0)
      max: 153 (0.6)
      mean: 19.299 (0.0756825)
      standard deviation: 16.1246 (0.0632336)
      kurtosis: 4.91164
      skewness: 1.86412
      entropy: 0.80384
    Green:
      min: 0 (0)
      max: 175 (0.686275)
      mean: 64.9195 (0.254586)
      standard deviation: 45.064 (0.176722)
      kurtosis: -0.898132
      skewness: 0.553704
      entropy: 0.968909
    Blue:
      min: 0 (0)
      max: 255 (1)
      mean: 144.561 (0.566908)
      standard deviation: 50.7463 (0.199005)
      kurtosis: -0.296128
      skewness: -0.559014
      entropy: 0.950698
  Image statistics:
    Overall:
      min: 0 (0)
      max: 255 (1)
      mean: 76.26 (0.299059)
      standard deviation: 40.2739 (0.157937)
      kurtosis: 11.4583
      skewness: 2.7144
      entropy: 0.907815
  Rendering intent: Perceptual
  Gamma: 0.454545
  Chromaticity:
    red primary: (0.64,0.33)
    green primary: (0.3,0.6)
    blue primary: (0.15,0.06)
    white point: (0.3127,0.329)
  Background color: white
  Border color: srgb(223,223,223)
  Matte color: grey74
  Transparent color: black
  Interlace: None
  Intensity: Undefined
  Compose: Over
  Page geometry: 276x183+0+0
  Dispose: Undefined
  Iterations: 0
  Compression: Zip
  Orientation: Undefined
  Properties:
    date:create: 2019-03-21T09:50:20+01:00
    date:modify: 2019-03-21T09:50:20+01:00
    png:IHDR.bit-depth-orig: 8
    png:IHDR.bit_depth: 8
    png:IHDR.color-type-orig: 2
    png:IHDR.color_type: 2 (Truecolor)
    png:IHDR.interlace_method: 0 (Not interlaced)
    png:IHDR.width,height: 276, 183
    png:sRGB: intent=0 (Perceptual Intent)
    signature: 217fe60358faf232f04ccc66dd92ec508fbf82b37858f0b954c87372720b88a1
  Artifacts:
    filename: index-opencv.png
    verbose: true
  Tainted: False
  Filesize: 89.3KB
  Number pixels: 50.5K
  User time: 0.000u
  Elapsed time: 0:01.000
  Version: ImageMagick 6.9.7-4 Q16 x86_64 20170114 http://www.imagemagick.org

mogirfy

唯一的区别是像素数据中的百分比很小。假设使用ImageMagick读取有损图像格式（如JPEG）将导致OpenCV读取时出现相同的图像是不合理的。格式本质上是有损的，并且解码器在它们实现的准确性和它们所做的权衡中可以有一定的自由裁量权。例如，OpenCV可能倾向于绝对速度和性能。 ImageMagick可能赞成兼容性和准确性。

不要忘记，尽管你只看到像素为0..255之间的整数，但它们实际上会转换为浮点数，转换为频域，量化，打包和压缩，然后在读取时反向发生。