Legacy ImageMagick Discussions Archive

Hi,

I have been having issues with the page speed of my site, and after a lot of research i am hoping Image Magick will sort it out.

I want to bulk convert lots of images in one folder then export all the images into an output folder folder.

Is this possible with a shell script? ie: Loop through all images from /input run the script below then output the optimised images in /output?

Here is what I have so far but this is doing one image at a time:

Code: Select all

convert /Users/bob/Desktop/image-magick/santorini.jpg -sampling-factor 4:2:0 -strip -quality 75 -resize 700x466! -interlace JPEG -colorspace RGB -background white -flatten /Users/bob/Desktop/image-magick/final/santorini-opt.jpg

Here is the report from my site of the errors i am trying to fix:
https://gtmetrix.com/reports/www.tinker ... m/ac0dMCTe

Any help would be great. I am very new to this, so if there is also anything I am missing or should add/remove to my script please let me know.

I am using command line on a mac.

Thanks
Paul

A shell script is possible. You should strip before setting any settings or operators. If on current IM, then use -colorspace sRGB if you want non-linear color and RGB if you want linear color. If on very old IM versions then reverse them.

Code: Select all

cd path2/inputdirectory
list=$(ls *.jpg)
for img in $list; do
inname=$(convert -ping $img -format "%t" info:)
convert $img -strip -colorspace RGB -resize 700x466! -background white -flatten -interlace JPEG -sampling-factor 4:2:0 -quality 75 path2/outputdirectory/${inname}.jpg
done

Hi, thanks for the reply

I keep getting the following message:

convert: unable to open image 'output/IMG_1297.JPG': No such file or directory @ error/blob.c/OpenBlob/3335.

I have altered the code to match my directory setup:

Code: Select all

#!/bin/bash

cd input
list=$(ls *.JPG)
for img in $list; do
inname=$(convert -ping $img -format "%t" info:)
convert $img -strip -colorspace RGB -resize 700x466! -background white -flatten -interlace JPEG -sampling-factor 4:2:0 -quality 75 output/${inname}.jpg
done

echo Success: Optimised images in /output

I only recently installed Image Magick so i think ill be on the latest version. I'm an obvious newbie to this, so not sure what that means about the linear etc. Are the settings i have got right to best optimise my images for best compression and quality!

Hope you can help

Cheers

IM won't create directories. Your command assumes that "output" is a subdirectory of "input". If that isn't true, the convert will fail with that error message.

Ah ok. Is it possible for the two folders to be seperate and not within input:

/test/run.sh (shellscript)
/test/input
/test/output

That's what ".." is for. Your output filename can be:

Code: Select all

../output/${inname}.jpg

That means "go up a level from the current directory, and look for "output" in that directory".

yeah got it, thanks for the help guys! All up and running.

Do i have the best settings for optimal compression and quality? Should i be using "sRGB" instead? Also the -sampling-factor 4:2:0, is that all ok?

Finally can you resize based on a % ratio rather than an exact size, like: -resize "700x466!"

pbul2004 wrote:... optimal compression and quality?

You can optimize one of the other but not both. They trade off each other.

Personally, I use two methods. When I don't really care about the results, I use "-quality 40". That's generally good enough quality, and very small.

When I do care about the results (eg my web pages) I iterate through quality settings to find the lowest quality (ie best compression) that is no more than 1% RMSE from the original image.

I've never played with "-sampling-factor" or "-interlace".

EDIT: Oops, I've just noticed your "-colorspace RGB". Why do you have that? If you use a recent version of IM, that is wrong.

I am using Version: ImageMagick 7.0.7-22 Q16 x86_64 2018-02-01

The colorspace RGB was something i found from an example, was never too sure if i actually needed or what it did.

Again, same with "-sampling-factor" or "-interlace". < Not sure if i even need these or what they do! They just got recommended on a post i found.

The images on my site are travel related, so i would like them looking sharp: https://www.tinkertravels.com/

However when i run GTMetrix scan the images are really bad : https://gtmetrix.com/reports/www.tinker ... m/ac0dMCTe

So hoping this will stop it complaining and fix them

pbul2004 wrote:The colorspace RGB was something i found from an example, was never too sure if i actually needed or what it did.

It makes your images linear, which is a really bad idea for the web. (In very old versions of IM, many years ago, it had the reverse effect).

snibgo wrote: ↑2018-02-14T13:22:19-07:00 It makes your images linear, which is a really bad idea for the web. (In very old versions of IM, many years ago, it had the reverse effect).

Should i totally remove this, or change it to sRGB?

It is best to keep it as -colorspace sRGB in case you have CMYK input images. Alternately, you would have to use profiles to change any CMYK inputs to sRGB outputs.

@fmw42 thanks.

just wanted to ask, is there a way to resize by a % based ration or something rather than specifying an exact size? Also what does -interlace do and -sampling-factor 4:2:0 not sure if these settings are right or what they actually do, any advice would be great, as id like to understand what it is i am doing

You can resize using %. So -resize 50x75% would resize to 50% width and 75% of height. http://imagemagick.org/script/command-l ... p#geometry If you want to do that exactly and not preserve aspect, you can add ! to the command, but it might distort the image. Interlace means the image will be drawn in interlace format, like window blinds as it displays. -sampling factor changes the ratio of YUV JPG channel compressions. http://imagemagick.org/script/command-l ... #interlace and http://imagemagick.org/script/command-l ... ling-facto

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Re: Bulk convert lots of images from one folder to another Shell Script loop

Re: Bulk convert lots of images from one folder to another Shell Script loop