On Tue, 11 Aug 2026 02:58:45 GMT, Prasanta Sadhukhan <[email protected]>
wrote:
>> If an image has RGBA encoding and all pixels are opaque, then
>> `SwingFXUtils.fromFXImage(image, null)` selects TYPE_INT_ARGB_PRE pixel
>> format but the JPEG ImageIO writer cannot encode this alpha-bearing image
>> pixel format since it has no support for it and returns false; so an empty
>> byte array is created.
>>
>> Issue is when `bimg` (used to store the returned pixel data from
>> `fromFXImage`) is null`, fromFXImage` uses the JavaFX PixelReader’s storage
>> format, not the alpha values of individual pixels.
>> For an RGBA PNG, JavaFX commonly decodes the pixels into premultiplied
>> ARGB/BGRA, so `fxFormat.getType()` is one of INT_ARGB_PRE/BYTE_BGRA_PRE so
>> `getBestBufferedImageType` returns `BufferedImage.TYPE_INT_ARGB_PRE` because
>> the pixel format has an alpha component. It does not inspect whether every
>> alpha value happens to be 255.
>>
>> The existing `fromFXImage` code only calls `checkFXImageOpaque()` when the
>> caller supplies a non-null `bImg` BufferedImage.
>> If `bImg `is null, all-opaque RGBA PNG produces an alpha-capable
>> BufferedImage i.e., BufferedImage.TYPE_INT_ARGB_PRE
>>
>> if (bimg == null) {
>> bimg = new BufferedImage(iw, ih, prefBimgType);
>> }
>>
>> and since JPEG has no standard alpha channel so it cannot store
>> transparency, so when `ImageIO.write(image, "jpg", out)` runs, ImageIO looks
>> for a registered JPEG writer which can encode that pre-multiplied-alpha
>> image type,
>> but the JPEG writer rejects an alpha-bearing BufferedImage, so
>> `ImageIO.write` finds no suitable writer and returns false
>> so OutputStream is not written into and have 0 bytes
>> [Basically the JPEG writer does not check whether the alpha values are all
>> 255; it only sees that the input image has an alpha channel and declines to
>> write it]
>>
>> The proposed JavaFX change avoids the rejection for an RGBA-formatted but
>> fully opaque image by returning TYPE_INT_RGB, which JPEG can encode.
>> ie., for a JavaFX image with an alpha-capable format but only opaque pixels,
>> `fromFXImage(image, null)` is made to choose RGB format rather than ARGB.
>> Additionally, checkFXImageOpaque is improved to scan one row at a time
>> instead of costly full-image scan so that unnecessary Color object for each
>> pixels is not created just to inspect alpha.
>>
>> A regression subtest is added to existing testcase
>>
>> ---------
>> - [x] I confirm that I make this contribution in accordance with the
>> [OpenJDK Interim AI Policy](https://openjdk.org/legal/ai).
>
> Prasanta Sadhukhan has updated the pull request incrementally with one
> additional commit since the last revision:
>
> Review comment
Marked as reviewed by angorya (Reviewer).
-------------
PR Review: https://git.openjdk.org/jfx/pull/2254#pullrequestreview-4928163329
