Prevent getting a brighter image when using pdftk

I used pdftk to extract the first page with

pdftk A=input.pdf cat A1 output output.pdf

or

pdftk input.pdf burst

The first page contains an image. This gets brighter in the output pdf. What can I do to prevent this and ensure that the page stays the same?

I suspect that there are some metadata which are not properly transported over to the output pdf. But that is just me guessing.