Mogrify resize to 50 percent images larger than 800px

[ManuO]

Hello,
My first post on the forum. I wanted to first thank the ImageMagick Team for the fantastic piece of software.

I am using mogrify to resize a set of images on Mac or Ubuntu using the following command:

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mogrify -resize 50% *.jpg

and the resulting images are produced properly.

My question is how do I resize only the images that are larger than 800px in the folder?
I have tried a few combinations without success.
For instance I tried:

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mogrify -resize 50% "800x>" *.jpg

without success.

Thanks for your help

[fmw42]

Either of these work fine for me on IM 6.8.8.2 Q16 Mac OSX Snow Leopard

I put my images in tmp1 and resize to tmp2 (they were 2 copies of logo: converted to png and one copy of rose: converted to png -- logo is 640x480 and rose is 70x46)

cd desktop/tmp1


mogrify -path ../tmp2 -format png -resize 500x500\> *.png

mogrify -path ../tmp2 -format png -resize "500x500>" *.png


Try 500x500 rather than 500 or 500x. Perhaps it needs the -format argument

In the future, please also identify the version of IM that you are using.

[snibgo]

I think ManuO wants to do something else.

For images larger than 800x800, he wants to resize them by 50%. For example, an image 3000x2000 will become 1500x1000.

For other images, smaller than 800x800, he doesn't want to resize them.

I don't think this is possible entirely within IM. It needs a script.

[ManuO]

Thanks snibgo,

You translated my question as intended. Would you know any sample script for achieving the needed result?

I checked Fred's Scripts page and the closest I can see is the aspect http://www.fmwconcepts.com/imagemagick/aspect/index.php, but I don't think it does what I need.

PS: I am using ImageMagick 6.8.7-7.

[snibgo]

What is your platform? For a Windows bat file:

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FOR /F "usebackq" %%D ^
IN (`identify -format "%%[fx:w>800&&h>800]" %1`) ^
DO if %%D==1 convert %1 -resize 50%% out.png

If you save that as possResize.bat, then typing ...

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possResize.bat x.jpg

... will resize x.jpg to make out.png if x.jpg is both higher and wider than 800. For smaller files, it does nothing.

This works on one file at a time. You could put that within a Windows For loop to process multiple files.

[ManuO]

Thanks Snibgo,

I just tried the batch script without success. When I run it there is no out.png file created even though I don't see an error.

I am running Windows 7. I can also run on Mac OS 10.9 or Ubuntu 13.10.

[snibgo]

Put these two lines at the top of your bat file.

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identify %1

identify -format "%%[fx:w>800&&h>800]" %1

What outputs do they give?

[ManuO]

Thanks Snibgo,

Now I am getting the desired result based on the size of the image. How could I apply to a bunch of files at the same time?

[snibgo]

Well, that's a scripting question, nothing to do with IM. But you could stick it inside an outer loop that loops through your files. Something like this:

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FOR %%F in (*.jpg) ^
DO FOR /F "usebackq" %%D ^
IN (`%IM%identify -format "%%[fx:w>800&&h>800]" %%F`) ^
DO if %%D==1 %IM%convert %%F -resize 50%% small\%%F

[fmw42]

Here is an IM only approach that uses mogrify for all png images in a folder and calculations within +distort srt to resize by 1/2=0.5 and 0 rotation, if both w and h are greater than 800.

#create new folder folder2 to hold the results from folder1, since mogrify will not autocreate the folder.

cd folder1
mogrify -path path2/folder2 -format png +distort srt "%[fx:(w>800 && h>800)?0.5:1] 0" *.png

If you want to resize if only w or h are greater than 800, then do

cd folder1
mogrify -path path2/folder2 -format png +distort srt "%[fx:(w>800 || h>800)?0.5:1] 0" *.png

see
http://www.imagemagick.org/Usage/basics/#mogrify
http://www.imagemagick.org/Usage/distorts/#srt

only distort allows in-line calculations

If the result is too blurry (from the EWA resampling), you can set the filter to point and optionally use one of -interpolate methods.

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Average
Average4
Average9
Average16
Background
Bilinear
Blend
Integer
Mesh
Nearest
NearestNeighbor
Spline

see
http://www.imagemagick.org/Usage/distorts/#lookup

[ManuO]

Thanks to both Snibgo and fmw42,

Both solutions worked fine.

[ingafreeman]

Thanks a lot it help me too. Cool infooo

[ManuO]

Hello again Snibgo,

Can you help with a last modification to my batch script?

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identify %1

identify -format "%%[fx:w>400]" %1

FOR /R %%a in (*.bmp) ^
DO FOR /F "usebackq" %%D ^
IN (`identify -format "%%[fx:w>400]" %%a`) ^
DO if %%D==1 mogrify "%%~fa" -resize 50%% %%a

The above works fine with folder and subfolder names not containing space but once there is a space it does not.

I get the following errors:

C:\imgs\test2>FOR /F "usebackq" %D IN (`identify -format "%[fx:w>400]" C:\imgs\test2\New folder\test3.bmp`) DO if %D == 1 mogrify "C:\imgs\test2\New folder\test3.bmp" -resize 50% C:\imgs\test2\New folder\test3.bmp
identify.exe: unable to open image `C:\imgs\test2\New': No such file or directory @ error/blob.c/OpenBlob/2643.
identify.exe: no decode delegate for this image format `C:\imgs\test2\New' @ error/constitute.c/ReadImage/555.
identify.exe: unable to open image `folder\test3.bmp': No such file or directory @ error/blob.c/OpenBlob/2643.

Would you know how to handle the folder name with spaces.

Thanks

[fmw42]

probably put double quotes around the folder names, at least that works on Mac.

[snibgo]

Yes, double quotes around the filenames.

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FOR /R %%a in (*.bmp) ^
DO FOR /F "usebackq" %%D ^
IN (`identify -format "%%[fx:w>400]" "%%a"`) ^
DO if %%D==1 mogrify "%%~fa" -resize 50%% "%%a"

As a rule, I ensure folders and filenames don't have spaces.