Thumbnail not properly generating from PNG images about thumbnailator

[gotson]

Thanks a lot @coobird , it solves my problem indeed!

[coobird]

@gotson, Thumbnailator uses the BufferedImage image type as the original when resizing the image. If the original image has a reduced number of colors, during the resize process, it will use reduced number of colors. As a result, we can end up with suboptimal results, including the issues you've seen.

One way to avoid this is to force Thumbnailator to use a different image type internally when processing by using .imageType(BufferedImage.TYPE_INT_ARGB). This also means that the resulting image will use that image type, which in this case is 8-bits per channel (with alpha, which is ignored when writing to JPEGs.)

Hence, if you modify your code to:

Thumbnails.of(imageBytes.inputStream())
        .size(300, 300)
        .imageType(BufferedImage.TYPE_INT_ARGB)
        .outputFormat("jpeg")
        .toOutputStream(os)

then, the problem with odd colors and poor resizing should be resolved.