qgis - How to make the white background of an RGB raster transparent?

I would like to show on my map only the reddish pixels of my raster layer.

Said in another way: I would like to transform my white background into transparent background so I can see my other features.

I have the feeling this is possible using the custom transparence tab in the layer property.

Answer

I found a solution to my problem:

In the transparency tab use the mouse selection tool to add a value from the screen by interactively clicking on a pixel. This will automatically add a new line in the table to the left showing the band characteristics of this pixel. Clicking on apply will then set to transparent all the pixels in the raster with the same pixel value.