Bug: Issue with Watermark Image Blending

[oscaruitenbroek]

Problem/Opportunity

A problem is reported on blending a .png watermark image on top of video playback we are not able to get the blending output as we expect. Following are the details of the issue:

Details:

1. Our Watermark system support 2 types of Graphics blending methods.

       a) straight-alpha 
   
       b) pre-multiplied alpha. 
   

2. A Translucent grey scale chessboard like .png image is drawn on top of the Video.

3. We are on Lightning 2.8. With the understanding that WebGL defaults to Pe-Multiplied alpha we had tried blending the Watermark image.

4. But the outcome of the blending was far from expected.

5. To check if the issue is global to the STB, we tried doing similar blending on WPE Browser as HTML apps . Here the outcome was quite Similar to expectation.

6. We tried both 2D Canvas and WebGL approach, both the outputs were off the expectation.

Snippet of the lightning config

"appSettings": {
"stage": {
"clearColor": "0x00000000",
"useImageWorker": true
},

Steps to reproduce

No response

Expected Behavior

Actual Behavior

Notes (Optional)

No response

[elsassph]

From a spec perspective I'm not sure it qualifies as a bug:

• PNG spec has that colors shouldn't be premultiplied,
• Android (and maybe iOS) do diverge from the spec by premultiplying their PNG assets, which causes complications as images loaded from network need to be handled differently.

So it sounds like potentially the watermarking service provides both variants to satisfy different use cases.

we tried doing similar blending on WPE Browser ans HTML apps

I'm curious now, can you elaborate?

Generally Lightning expects that PNGs (and canvas and base64) images have transparency and aren't premultiplied, so it will tell webGl to do the transformation when uploading the texture.