ImageMagick单转换命令性能 [英] ImageMagick single convert command performance

问题描述

我有几千个要处理的图像，因此每毫秒都很重要。每张图片的大小约为2-3Mb。

输入到转换器的源文件：
image.jpg

要从源生成的文件：

  orig_image.jpg //原始图片
 1024x768_image。 jpg // large image 
 250x250_image.jpg // thumbnail 1 
 174x174_image.jpg // thumbnail 2 
  

在浏览imagemagick转换性能的不同主题时，我感觉单个命令应该比每个图像大小的单个转换更快。此外，还提到了内存利用率作为性能提升。 （

I have a few thousand images to be processed so each millisecond counts. Each image is ~2-3Mb in size.

Source file fed to the converter: image.jpg

Files to be generated out of the source:

orig_image.jpg      // original image
1024x768_image.jpg  // large image
250x250_image.jpg   // thumbnail 1
174x174_image.jpg   // thumbnail 2

While browsing different topics on imagemagick convert performance I got a feeling that a single command should be way faster than individual converts for each image size. Also a memory utilization was mentioned as a performance boost. (ImageMagick batch resizing performance)

Multiple command conversion (each command run via php's exec() in a loop):

convert "image.jpg" \
    -coalesce -resize "1024x768>" +repage "1024x768_image.jpg"

convert "1024x768_image.jpg" \
    -coalesce \
    -resize "250x250>" \
    +repage \
    -gravity center \
    -extent "250x250" "250x250_image.jpg"

convert "1024x768_image.jpg" \
    -coalesce \
    -resize "174x174>" \
    +repage \
    -gravity center \
    -extent "174x174" "174x174_image.jpg"

mv image.jpg orig_image.jpg

Single command conversion incorporating ImageMagicks mpr:

convert "image.jpg" -quality 85 -colorspace rgb -coalesce \
    -resize "1024x768>" \'
    -write "1024x768_image.jpg" \
    -write mpr:myoriginal +delete \
    mpr:myoriginal -coalesce \
    -resize "250x250>" \
    -gravity center \
    -extent "250x250" \
    -write "250x250_image.jpg" +delete \
    mpr:myoriginal -coalesce \'
    -resize "174x174>" \
    -gravity center \
    -extent "174x174" \
    -write "174x174_image.jpg"

After performance testing the results are somewhat unexpected. Single command convert in a loop finishes in 62 seconds while multiple command conversion executes in just 16 seconds?

# convert -version
Version: ImageMagick 7.0.2-1 Q8 i686 2017-02-03 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2016 ImageMagick Studio LLC
License: http://www.imagemagick.org/script/license.php
Features: Cipher DPC HDRI OpenMP
Delegates (built-in): bzlib freetype jng jpeg lzma png tiff wmf xml zlib

Also installed libjpeg-turbo jpg processing library but I cannot tell (don't know how to check) if ImageMagic is using it or the old libjpeg.

Any ideas how to speed up image converting process?

Edit: Don't know how to format it properly here on stackoverflow, but I just noticed that single line command had an argument "-colorspace rgb" and multiple line commands did not which actually results in such strange results where multiple commands are processed faster.

Removed the "-colorspace rgb" argument after which the MPR convert version works the best and gave additional boost in performance.

To sum it all up I ended up using this command:

// MPR
convert "orig_image.jpg" -quality 80 -coalesce \
    -resize "1024x768>" \
    -write 1024x768_image.jpg \
    -write mpr:myoriginal +delete \
    mpr:myoriginal -resize "250x250>" \
    +repage -gravity center -extent "250x250" \
    -write "250x250_image.jpg" \
    -write mpr:myoriginal +delete \
    mpr:myoriginal -coalesce -resize "174x174>" \
    +repage -gravity center -extent "174x174" \
    -write "174x174_image.jpg"

解决方案

Eric's and John's suggestions share much wisdom, and can be mixed in with my suggestion - which is to use GNU Parallel. It will REALLY count when you have thousands of images.

I created 100 images (actually using GNU Parallel, but that's not the point) called image-0.jpg through image-99.jpg. I then did a simple resize operation just to show how to do it without getting too hung up on the ImageMagick aspect. First I did it sequentially and it took 48 seconds to resize 100 images, then I did the exact same thing with GNU Parallel and came in under 10 seconds - so there are massive time savings to be made.

#!/bin/bash
# Create a function used by both sequential and parallel versions - it's only fair
doit(){
   echo Converting $1 to $2
   convert -define jpeg:size=2048x1536 "$1" -resize 1024x768 "$2"
}
export -f doit

# First do them all sequentially - 48 seconds on iMac
time for img in image*.jpg; do
   doit $img "seq-$img"
done

# Now do them in parallel - 10 seconds on iMac
time parallel doit {} "par-{}" ::: image*.jpg

Just for kicks - watch the CPU meter (at top right corner of the movie) and the rate the files pop out of GNU Parallel in the last 1/6th of the movie.

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