How to change an all black image to a Pantone color

[rtloon]

I have a quite posterized jpg image that is currently black on white. I'd like to change the black to a specific PMS color.  I've got a swatch of the PMS color I want. But I don't know how to select all the full black and tinted black pixels, and once selected how to effect the change. Using the selection tool to choose areas and then the paint bucket tool to change each of them is cumbersome and problematic in capturing all the black pixels. 

[thomaso]

If you save the .jpg as a grayscale .tiff then you can assign a fill color swatch which affects the black.

[rtloon]

OK. Created a greyscale 16 bit .tiff file. Opened it in Affinity Photo. Unlocked the image.

Tried to change the color profile from greyscale to CMYK or RGB. All colors remained greyscale. (see photo). This includes all swatches and Pantone colors displayed in greyscale.

Adjusting the color of the black fill disk to grey did not impact the image: all the black remained black.

[Alfred]

Add a Fill layer, change the blend mode of the new layer to ‘Screen’ and set the fill colour to whatever you want.

[rtloon]

Didn't work on the greyscale tiff, but worked fine on the original Affinity Photo file! Thanks, Alfred!

[thomaso]

1 hour ago, rtloon said:

Created a greyscale 16 bit .tiff file. Opened it in Affinity Photo. Unlocked the image.

Tried to change the color profile from greyscale to CMYK or RGB.

Oh, sorry, I had Affinity Designer or Publisher in mind with my answer. Even there it isn't complicated: 

1. Place the grayscale image.
2. Select a Pantone fill color swatch. 

Btw, it also works with grayscale .png or .jpg. (don't save it in 16 bit, 8 is enough.)