Blocks in PDF output

[mmmmmmmm]

I just finished my family photo album and export it to PDF. Unfortunately in the PDF on two photo's blocks appear, see the example in the picture below. This happens with a opacity of 85% and when I increase it to about 100% these blocks do not appear. However, I like to set the opacity to 85% (or get the effect of it) since that photo is used as a background image. I played around with the PDF export settings and the number and sometimes a slight color change in those block happens.

 

What is causing this and how can it be avoided?

 

[Alfred]

28 minutes ago, mmmmmmmm said:

I like to set the opacity to 85% (or get the effect of it)

I’m afraid I don’t know what’s causing the problem you describe, but you can achieve a similar effect by covering the picture with a white rectangle and reducing the opacity of that rectangle to 15% or so.

[mmmmmmmm]

I did found a workaround or I did it wrong. With the opacity of the picture frame set to 100% and that of the picture to 85% I do not get any blocks in the output PDF. The effect is similar so it helps for now and I can order the book. However, I am still wondering what went wrong, or what is the difference between those two ways of setting to opacity.