Resize Image files

I have a lot of images that taken by my Digital camera with very high resolution 3000 * 4000 and it takes a lot of Hard disk space, I used Photoshop to open each Image and re-size it o 开发者_如何学Pythonbe with small resolution, but it needs a lot of time and effort

I think that I can write simple program that open the folder of images and read each file and get it's width and height and if it's very high change it and overwrite the image with the small one.

Here some code I use in a Java-EE project (should work in normal application to:

int rw = the width I needed;

BufferedImage image = ImageIO.read(new File(filename));

ResampleOp  resampleOp = new ResampleOp(rw,(rw * image.getHeight()) / image.getWidth() );
resampleOp.setFilter(ResampleFilters.getLanczos3Filter()); 
image = resampleOp.filter(image, null);

File tmpFile = new File(tmpName);
ImageIO.write(image, "jpg", tmpFile);

The resample filter comes from java-image-scaling library. It also contains BSpline and Bicubic filters among others if you don't like the Lanczos3. If the images are not in sRGB color space Java silently converts the color space to sRGB (which accidentally was what I needed).

Also Java loses all EXIF data, thought it does provide some (very hard to use) methods to retrieve it. For color correct rendering you may wish to at least add a sRGB flag to the file. For that see here.

+1 to what some of the other folks said about not specifically needing Java for this, but I imagine you must have known this and were maybe asking because you either wanted to write such a utility or thought it would be fun?

Either way, getting the image file listing from a dir is straight forward, resizing them correctly can take a bit more leg work as you'll notice from Googling for best-practices and seeing about 9 different ways to actually resize the files.

I wrote imgscalr to address this exact issue; it's a dead-simple API (single class, bunch of static methods) and has some good adoption in webapps and other tools utilizing it.

Steps to resize would look like this (roughly):

1. Get file list
2. BufferedImage image = ImageIO.read(files[i]);
3. image = Scalr.resize(image, width);
4. ImageIO.write(image);

There are a multitude of "resize" methods to call on the Scalr class, and all of them honor the image's original proportions. So if you scale only using a targetWidth (say 1024 pixels) the height will be calculated for you to make sure the image still looks exactly right.

If you scale with width and height, but they would violate the proportions of the image and make it look "Stretched", then based on the orientation of the image (portrait or landscape) one dimension will be used as the anchor and the other incorrect dimension will be recalculated for you transparently.

There are also a multitude of different Quality settings and FIT-TO scaling modes you can use, but the library was designed to "do the right thing" always, so using it is very easy.

You can dig through the source, it is all Apache 2 licensed. You can see that it implements the Java2D team's best-practices for scaling images in Java and pedantically cleans up after itself so no memory gets leaked.

Hope that helps.

You do not need Java to do this. It's a waste of time and resources. If you have photoshop you can do it with recording actions: batch resize using actions

AffineTransformOp offers the additional flexibility of choosing the interpolation type, as shown here.

You can individually or batch resize with our desktop image resizing application called Sizester. There's a full functioning 15-day free trial on our site (www.sizester.com).