png images becomes black after converting to pdf

[e-no91]

I've used transformDocument from "image/png" to "image/tiff" and finally to "application/pdf" to convert from PNG image to PDF file.
However, the results is an image with black colour. Why does it becomes like this?

It works well with bmp and jpg/jpeg files.

Thank you in advance!

[ratik_singhal]

While converting "image/png" to "image/tiff", are you using any custom code or using custom properties. I think you might be using imagemagick for that.

[e-no91]

I directly use the transformDocument function.
I've managed to remove the black colours in pdf by converting "image/png" to "image/bmp" first, before converting it to "image/tiff", then "application/pdf".