How would I make white transparent and anything close to white semi transparent

[BNTKids-Studios]

So, I have an image with a white background. The creator of it, who created it for me, told me that she cannot undo the white background, as she's already finalized the project and disposed of the original works.

How do I make anything completely one color and it's similar colors transparent? Like, the color itself is fully transparent, while similar colors are semi-transparent. can I use a mask to achieve this effect?

[Marja de Klerk]

Hi, I hope I understand correctly what you are trying to do. Do you want to make the white background transparant? In that case you have to make a duplicate of the layer. In the duplicate layer you can select the white background and delete it. This will make the background transparant. 

For the similar colors you can use a mask and lower the opacity to make it semi-transparant.

[BNTKids-Studios]

I know how to create a mask, but when I lower the opacity, it changes the entire image of colors.

[JJMack]

Use a script, action, plug-in or do the steps yourself to perfectly remove white