Photoshop :: Newbie Question On Color/contrast

Hi I placed some advertisments into a black-and-white (greyscale) newspaper. The ads were previously scanned images and I received them as high-resolution .JPG's. I don't have access to the original files. When they printed, some of the ads were not as vivid as I wanted. I opened them up in Photoshop and found out that the blacks are not 100% black. Some were 90%, some as low as 40%. They looked fine on my monitor and on the laser printer proofs, but on newsprint they were not dark enough. I want to increase the blacks to 100%. I'm a Photoshop newbie, so the only solution I can come up with is to open each of these ads and use the curves tool to manually pull all of the blacks up to 100% while leaving the white part of the spectrum alone. I'm not sure I'm using the curves tool correctly. Not to belabor the point, but here some screen shots of before and after. BEFORE:  AFTER:If you look carefully, you can see the curves. Bassically I pulled up all of the curve to 100 percent black and just left the leftmost point where it is(which I assume is the white part of the spectrum). Is this the best approach for doing what I want to do? Thanks.