B4J Question non-ui - resize image in byte array without javafx

[Alexander Stolte]

I get a image as byte on my server, i want to create a smaller image of it to use it as thumbnail. I want to avoid having to use javafx. Is that possible?

 

[emexes]

If you can get that image to be uncompressed, ie a 2D array of pixels, then: no worries.

The simplest algorithm is sampling every nth row and column to reduce the image to 1/nth of original size.

The next-simplest is to average each n-x-n block of pixels to produce 1 pixel in the 1/nth thumbnail.

If the thumbnail is not an integer reduction (?) of the original image, then it gets a little trickier if you want to be exactly correct, but in reality is probably a case of: close enough is good enough.

 

[Erel]

Two options based on jShell:

- Create a small UI app without a form that creates the image.
- Use FFMPEG tool.

 

[xulihang]

You can also use OpenCV which has a java library

 

[tchart]

I wrapped a library called Thumbnailator to do just this. I have used it a while so the library may be out of date but it worked when I used it - edit: actually I see it had a release recently so Ive recompiled against that version.

Dim thumb As Thumbnailator

Dim PreviewBytesJpg() As Byte
Dim PreviewBytesPng() As Byte

'This creates a thumbnail of 250px wide, the height is zero which means it will auto calculate based on the aspect of the image
PreviewBytesJpg= thumb.CreateThumbnail(ResultBytes,250,0) 'Returns a JPEG
PreviewBytesPng= thumb.CreateThumbnail2(ResultBytes,250,0) 'Returns a PNG which can be transparent

 

[Alexander Stolte]

I wrapped a library called thumbnailanator to do just this. I have used it a while so the library may be out of date but it worked when I used it.

but the library is still being updated. Let's see, thanks for the tip!

GitHub - coobird/thumbnailator: Thumbnailator - a thumbnail generation library for Java

Thumbnailator - a thumbnail generation library for Java - coobird/thumbnailator

github.com

 

[tchart]

but the library is still being updated. Let's see, thanks for the tip!

GitHub - coobird/thumbnailator: Thumbnailator - a thumbnail generation library for Java

Thumbnailator - a thumbnail generation library for Java - coobird/thumbnailator

github.com

Yes I just saw that now and I have recompiled. There was a large gap in development (2014-2020)

 

[Alexander Stolte]

Thank you very mutch! i'll give it a try.

 

[tchart]

Thank you very mutch! i'll give it a try.

Alexander, let me know if you need any other methods exposed in the wrapper. I only exposed those two for my needs as I was converting the bytes to a base64 image and not writing to disk.

 

[Alexander Stolte]

Alexander, let me know if you need any other methods exposed in the wrapper. I only exposed those two for my needs as I was converting the bytes to a base64 image and not writing to disk.

i have this problem that i can't compile.

javac 1.8.0_191
src\net\myproject\api\my_handler.java:410: error: cannot access ThumbnailatorWrapper
nz.ope.thumbnailator.ThumbnailatorWrapper _thumb = null;
                    ^
  bad class file: D:\OneDrive\B4X Libs\b4j\thumbnailator.jar(nz/ope/thumbnailator/ThumbnailatorWrapper.class)
    class file has wrong version 55.0, should be 52.0
    Please remove or make sure it appears in the correct subdirectory of the classpath.
1 error

The library already has nice functions, I would do it too if I knew how.

 

[DonManfred]

I guess you should update to java 11 or java 14

 

[Alexander Stolte]

I guess you should update to java 11 or java 14

Your'e right, but now i need this library, because on java 11 i cant use jFX in a non-ui project. ?

But the thumbnail creation works very well, the images that were 50kb in size by my old function are now 10kb in size, because I don't divide the normal size by 2 anymore.

Alexander, let me know if you need any other methods exposed in the wrapper. I only exposed those two for my needs as I was converting the bytes to a base64 image and not writing to disk.

Thank you, the watermark option would still be nice and would be another feature I want to add later.

 

[Alexander Stolte]

Alexander, let me know if you need any other methods exposed in the wrapper.

the watermark option would still be nice

did you have time to do that in the next days?