Further investigation and work done for better compatibility of transparency (PDF-289) has shone some light on the issue. The xObject containing the base image contains an /matte attribute which specifies a color the image was pre blended with. The specification states:
"When preblended image data is used in transparency blending and compositing computations, the results shall be the same as if the original, unblended image data were used and no matte colour were specified. In particular, the inputs to the blend function shall be the original colour values. To derive c from c′, the conforming reader may sometimes need to invert the formula shown previously. The resulting c value shall lie within the range of colour component values for the image colour space."
I'll need to experiment to see if we can correct of the preblended colour.
Bug
Major
Further investigation and work done for better compatibility of transparency (
PDF-289) has shone some light on the issue. The xObject containing the base image contains an /matte attribute which specifies a color the image was pre blended with. The specification states:"When preblended image data is used in transparency blending and compositing computations, the results shall be the same as if the original, unblended image data were used and no matte colour were specified. In particular, the inputs to the blend function shall be the original colour values. To derive c from c′, the conforming reader may sometimes need to invert the formula shown previously. The resulting c value shall lie within the range of colour component values for the image colour space."
I'll need to experiment to see if we can correct of the preblended colour.