Resizing strategy

I cannot use this lib which looks very good because of a missing functionnality 
: Resizing strategy.

I mean, that there is different way to generate a thumbnail, if I ask a 
thumbnail of 100x100
I'd like to choose if 
1. I will keep the ratio by fitting to the biggest dimension (but i will not 
have 100x100 result)
2. I will crop the image 
3. I will add empty area around to have exactly 100x100
4. I will not keep the ratio

As I have seen I can do 1. and 4. but I didn't see how to do 2. and/or 3.
If it exists, forgive me and please consider this as a documentation issue.

I'm sure I will use your lib later but without this functionnality I cannot in 
my current project and I'm going to code again some ugly code for resizing 
images

Original issue reported on code.google.com by [e-mail] on 29 Aug 2011 at 3:24

[GoogleCodeExporter]

Thank you for the feedback.

There definitely should be more documentation for Thumbnailator, especially 
when it comes to how to deal with certain use cases.

> 2. I will crop the image 

If you want to specify a section of an image before creating a thumbnail, one 
can use the `sourceRegion` method:

  Thumbnails.of("path/to/image")
    .sourceRegion(200, 200, Positions.CENTER)
    .size(100, 100)
    .toFile("path/to/thumbnail");

The above code will take the center 200x200 region, and resize it to a 
thumbnail that is 100x100.

If what is desired is to merely crop an image, Thumbnailator does not provide a 
direct way to do so, however there is a `Canvas` image filter which can perform 
image cropping. (Please refer the javadocs at 
http://thumbnailator.googlecode.com/hg/javadoc/net/coobird/thumbnailator/filters
/Canvas.html)

> 3. I will add empty area around to have exactly 100x100

The aforementioned `Canvas` image filter has a feature to forcefully make 
thumbnails a certain size.

For example, say we take a 200x400 image and scale it down to 50x100, then we 
want to have an empty area to make a 100x100 thumbnail. The code can be written 
as follows:

  Thumbnails.of("path/to/image-200x400")
    .size(100, 100)
    .addFilter(new Canvas(100, 100, Positions.CENTER))
    .toFile("path/to/thumbnail");

Note: `size(100, 100)` will preserve the aspect ratio of the original, so the 
thumbnail without the `Canvas` filter would be 50x100.

Please let me know if there's anything I missed or anything else I can help you 
with.

Original comment by [e-mail] on 29 Aug 2011 at 3:53

[GoogleCodeExporter]

*Note to self*

I'm going to add this as a note that Issue 24 seems to be a similar request to 
the resizing strategy #2.

Maybe adding a `crop` method to handle a call to the `Canvas` filter would be a 
better solution.

Original comment by [e-mail] on 29 Oct 2011 at 3:36