I have created a heatmap in QGIS to cover my point data and I have saved it as geoTiff so that I can import into tilemill, which I managed to do but my background is black .In QGIS however I want to make the background of the layer transparent not black so that it shows my heatpoints/areas only . I hahve tried playing around with singleband and changing to singleband pseudocolor but this then removes the heat map coverage and leaves single coordinate points?
Right Click on the layer name and then left click "Properties", then click the "Transparency" tab. In the box Headed "Transparency Pixel List" click the right hand icon marked with an arrow and a ? ("Add Values from Display"). Then click the black area on the display that you would like transparent. Then click OK. All black area with the same value will now be transparent.