In the fuzzy select tool options, there is a threshold setting, The default value is 15 increase the value and select until the faint background marks are no longer selected. The same holds true for other select tools such as color select.
Edit: Apologies you want to keep the faint parts, reduce the threshold value and select until they remain.
screenshots, note the select tool modes, you can change mode to add/subtract from an existing selection. Remember to to reset to the default replace when complete. https://i.imgur.com/KB2tCVT.jpg
Another way is use a quickmask to paint in/out a selection. https://docs.gimp.org/2.10/en/gimp-image...utton.html Select -> Toggle Quickmask With it on, White will paint out a selection and Black will add a selection.
screenshot: Half painted out a background blemish selection and added a part the fuzzy select missed. Then toggle off, cut selection. https://i.imgur.com/KOVPeww.jpg
Edit: Apologies you want to keep the faint parts, reduce the threshold value and select until they remain.
screenshots, note the select tool modes, you can change mode to add/subtract from an existing selection. Remember to to reset to the default replace when complete. https://i.imgur.com/KB2tCVT.jpg
Another way is use a quickmask to paint in/out a selection. https://docs.gimp.org/2.10/en/gimp-image...utton.html Select -> Toggle Quickmask With it on, White will paint out a selection and Black will add a selection.
screenshot: Half painted out a background blemish selection and added a part the fuzzy select missed. Then toggle off, cut selection. https://i.imgur.com/KOVPeww.jpg