ben-biddington
commented
2 months ago I suspect it is due to falling into this jpeg conversion?
I notice that when I download the image from Signal Desktop it has been converted to a jpeg.
For example:
https://upload.wikimedia.org/wikipedia/commons/4/47/PNG_transparency_demonstration_1.png
Whether or not the image is converted to jpeg depends on file size ((not dimensions) ) (1) and quality (2).
This 63kB file does preserve its transparency for example as it exits early at the size <= thresholdSize guard.
// ts/util/scaleImageToLevel.ts
//...
const level = highQuality ? MediaQualityLevels.Three : getMediaQualityLevel();
const {
maxDimensions,
quality,
size: targetSize,
thresholdSize,
} = MEDIA_QUALITY_LEVEL_DATA.get(level) || DEFAULT_LEVEL_DATA; // <------------------ (2)
if (size <= thresholdSize) { // <---------------------------------------------------- (1)
// Always encode through canvas as a temporary fix for a library bug
const blob: Blob = await canvasToBlob(data.image, contentType);
return {
blob,
contentType,
};
}
for (let i = 0; i < SCALABLE_DIMENSIONS.length; i += 1) {
const scalableDimensions = SCALABLE_DIMENSIONS[i];
if (maxDimensions < scalableDimensions) {
continue; // <------------------------------------------------------------------- (2)
}
// We need these operations to be in serial
// eslint-disable-next-line no-await-in-loop
const blob = await getCanvasBlobAsJPEG(
data.image,
scalableDimensions,
quality
);
if (blob.size <= targetSize) {
return {
blob,
contentType: IMAGE_JPEG,
};
}
}
const blob = await getCanvasBlobAsJPEG(data.image, MIN_DIMENSIONS, quality);
return {
blob,
contentType: IMAGE_JPEG,
};
Using a supported version?
Overall summary
When an user sends transparent png to another person, png automatically converts with a black background. When image is selected as a file, it's the same.
Steps to reproduce
Expected result
File shouldn't be changed.
Actual result
File changes.
Screenshots
No response
Signal version
7.14.0
Operating system
Windows 11
Version of Signal on your phone
No response
Link to debug log
No response