How to get a good quality thumbnail

Question

I am trying to create a high quality thumbnail of this image, with Java and Scalr 3.2

Answer 1

If you want high quality result, so use [RapidDecoder][1] library. It is simple as follow:

import rapid.decoder.BitmapDecoder; ... Bitmap bitmap = BitmapDecoder.from(getResources(), R.drawable.image) .scale(width, height) .useBuiltInDecoder(true) .decode(); Don't forget to use builtin decoder if you want to scale down less than 50% and a HQ result.

Answer 2

@Stivlo, I am sorry for not replying to this, I never got any notification from SO about the question.

java-image-scaling does have some nice filters to help with fine-tuning if you need it. That said, in v4.2 of imgscalr I added the new ULTRA_QUALITY that might get you closer to what you want.

I hope that helps, but realize this is being replied to almost a year after the fact unfortunately. Sorry about that.

Answer 3

I have run the same tests and java-image-scaling definitively have better results for thumbnails smaller than 250px. It also support sharp filtering, which make the results better.

I keep both libraries since the syntax of Scalr is often easier, with only one line.

Answer 4

This is not a complete answer to your question, but:

Regarding JPEG quality:

Compression quality can be set using a ImageWriteParam as described here. They suggest using an int value of 0|1 but I believe that you should actually specify a float value between 0.0 and 1.0.

Regarding your scaling dimension issues:

From the Scalr homepage:

NOTE: If a width and height are provided that violate the image’s proportions (e.g. attempt to resize an 800×600 image to a 150×150 square) the library will first look at the orientation of the image (landscape/square or portrait) and then select the primary dimension (landscape or square uses width, portrait uses height) to recalculate a correct secondary dimension; ignoring what was passed in by the user that was violating the proportions.

In your case the primary dimension will be a width of 77 and thus your height limit of 57 will be ignored.

Answer 5

Note that if your images have an alpha channel, both libraries are problematic. I'm only talking about shrinking images, I haven't tested enlarging them.

java-image-scaling may create an ugly border around the transparent edges depending on the image, and this looks very bad. I found no way to avoid this.

Scalr is only problematic using the (ultra) quality modes. It can easily be used in a way that works fine, though: bicubic interpolation leaves artifacts in transparent images, so you may want to avoid it. Since it's the default for (ultra) quality images, and scaleImageIncrementally() is protected you'd have to subclass it for this, though, if you want the quality (a fraction higher than 2 looks very blurry with bilinear filtering, though).