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Optimizing Image Cropping and Writing Performance with Ruby Vips #406
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Hi,
I’m working on a project that uses Ruby Vips to crop and adjust images for printing. However, I’ve encountered performance issues, specifically with the speed of writing the cropped image to a file. The writing process is quite slow, and I’d like to know how I can optimize this further to speed up the entire operation, as I need to transmit the processed image as quickly as possible.
Here’s the relevant code I’m using for cropping the image:
class ImageCropVips def self.crop(image_path) img = Vips::Image.new_from_file(image_path) bbox = Trimer.find_trim(img) dpi = (img.xres > 0 ? img.xres : 11.81) * 25.4 puts "\n VIPS bbox: #{bbox}, dpi: #{dpi} \n" if bbox tmp = Tempfile.new(["tmp", '.png']) img.crop(*bbox).write_to_file(tmp.path, Q: 100) else nil end end end class Trimer def self.find_trim(image) return [0, 0, image.width, image.height] if image.bands < 4 alpha_channel = image.extract_band(3) _, first_row = alpha_channel.profile left = first_row.min _, first_row = alpha_channel.fliphor.profile right = image.width - first_row.min first_column, = alpha_channel.profile top = first_column.min first_column, = alpha_channel.flipver.profile bottom = image.height - first_column.min width = right - left height = bottom - top [left, top, width, height] end end
The trimming works fine, but the file writing step (write_to_file) takes a significant amount of time. Do you have any suggestions for speeding up the writing process or improving overall performance? Any insights would be greatly appreciated!
Thank you!
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Replies: 1 comment 5 replies
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Hi @JohnAnon9771,
find_trim is built into libvips, and you can use [n] for band extract. You can probably write (untested):
img = Vips::Image.new_from_file(image_path) bbox = img[3].find_trim img.crop(*bbox).write_to_file("x.png")
How large are these files? PNG is a very slow format, so if the images are large, write will take a long time. Are there any other formats you could use? webp or tiff would probably be quicker.
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Yes, they are 4200x4800 png images, with an average size of 10mb. Unfortunately, I can only use png, as the image will be sent to a printer that only accepts png.
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Ah, shame. Yes, it'll be slow:
$ time vips crop wtc.jpg x.png 0 0 4200 4800
real 0m1.755s
user 0m1.883s
sys 0m0.191s
So 1.75s just for a 4800 x 4200 PNG write on this Ubuntu 24.04 PC. PNG write is single-threaded, sadly.
Most PNG write time is spent in libz, so it might be worth experimenting with other versions. It's such a critical library that many people have attempted faster implementations, for example libz-ng:
https://github.com/zlib-ng/zlib-ng
You can also disable PNG zip compression. This makes it a lot quicker, though files will be larger:
$ time vips crop wtc.jpg x.png[compression=0] 0 0 4200 4800
real 0m0.434s
user 0m0.328s
sys 0m0.279s
$ ls -l x.png x0.png
-rw-r--r-- 1 john john 60584302 Oct 18 14:03 x0.png
-rw-r--r-- 1 john john 46732001 Oct 18 14:03 x.png
600k vs. 470k.
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Or tiff with zlib compression:
$ time vips crop wtc.jpg x.tif[tile,compression=deflate] 0 0 4200 4800
real 0m1.009s
user 0m1.128s
sys 0m0.194s
$ ls -l x.tif
-rw-r--r-- 1 john john 37114608 Oct 18 14:07 x.tif
Almost twice as fast as PNG, with much better compression. PNG really is a poorly designed format.
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Thank you very much for the super detailed answer! I'll try to do it without compression, it really did increase the speed a lot. One question: does zlib-ng work automatically with libvips? How can I use it?
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You might need to rebuild libpng, or libspng. You'd have to experiment.
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