Carrierwave: resize image to fixed width and height

Question

I have a rails 4 app, where I allow users to upload images. I have validations in place for min dimension of 640X385 and thus a min aspect ratio of 1.6623376623376624. Now that means user can't upload smaller images either in terms of dimension or aspect ratio. And when they upload a bigger image, it gets resized by ImageMagick's resize_to_fit method. But it resizes to a proportional width and height and my dimension's validation fails. If I use resize_to_fill, even the smaller images get stretched and bypass aspect ratio's validation. So How do I get the resize method to resize an image perfectly to 640X385 dimension?

Tell me, what results do you expect if you resize a 1000x1000 image to 640x385? — Mark Setchell
I basically want the resize_to_fit to run BEFORE manipulate! in class MyImageUploader < BaseUploader — Vivek Tripathi
You didn't answer me. I asked you what it would look like, you told me when it would get processed. — Mark Setchell
Actually i have another image that i will be overlapping over the uploaded image. Now the problem is the overlapping image is fixed in size and dimensions. So I want my images to be too of a certain dimension. And thus I want uploaded images to be of 640X385 resolution. — Vivek Tripathi

UlfR UlfR · Accepted Answer · 2015-03-17T14:24:07

So I do not know exactly what result you expect for various sizes. I tend to use ImageMagick on the commandline so I produced a small script with examples that may or may not help you:

#!/bin/bash

# cleanup
rm *.jpg

# as expected
convert -size 640x385 xc:white img0.jpg
# bigger aspect ratio (2.0)
convert -size 800x400 xc:white img1.jpg
# lower aspect ratio (1.0)
convert -size 800x800 xc:white img2.jpg
# bigger aspect ratio (2.0) but to small
convert -size 400x200 xc:white img3.jpg
# lower aspect ratio (1.0) but to small
convert -size 200x200 xc:white img4.jpg

for img in img*; do
    # resize images to fit in box but keep aspect ratio
    convert ${img} -resize 640x385 r1.${img}
    # resize images keeping the aspectratio to fit in box. But only shrink
    # images, images that are to small is not enlarged.
    convert ${img} -resize 640x385\> r2.${img}
    # resize images ignoring the aspectratio to fit in box. But only shrink
    # images, images that are to small is not enlarged.
    convert ${img} -resize 640x385\>\! r3.${img}
done

identify  -format "%f: %w %h\n" *.jpg

The output is as follows:

img0.jpg: 640 385
img1.jpg: 800 400
img2.jpg: 800 800
img3.jpg: 400 200
img4.jpg: 200 200
r1.img0.jpg: 640 385
r1.img1.jpg: 640 320
r1.img2.jpg: 385 385
r1.img3.jpg: 640 320
r1.img4.jpg: 385 385
r2.img0.jpg: 640 385
r2.img1.jpg: 640 320
r2.img2.jpg: 385 385
r2.img3.jpg: 400 200
r2.img4.jpg: 200 200
r3.img0.jpg: 640 385
r3.img1.jpg: 640 385
r3.img2.jpg: 640 385
r3.img3.jpg: 400 200
r3.img4.jpg: 200 200

My guess is that you are looking for the last variant where the output is named r3.<something>.

For more info and good examples of how to use resize: http://www.imagemagick.org/Usage/resize/

Also have a look at: Resizing the image with padding using convert on ubuntu

I hope this helps.

Carrierwave: resize image to fixed width and height

1 Answers