Archived posting to the Leica Users Group, 2003/03/11
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]This is where the LUG shines. No nonsense how-to's ... thanks. Daniel At 15:14 11.03.2003 -0500, you wrote: >On Tuesday, March 11, 2003, at 02:44 PM, Martin Howard wrote: > >>Occasionally, I need to increase contrast locally in an image. For >>example, the face in an environmental portrait may be a bit flat, i.e. it >>only spans a few levels from the darkest to the lightest pixels. >>In a darkroom, you'd fiddle this with dodging and burning typically >>combined with a different grade contrast filter on VC paper. >> >>However, in Photoshop, I'm lost. What I'd ideally like to do is get >>Photoshop to do is two things: pull apart the end points in a local >>region (masked off by a selection) and then "fill in the blanks" in the >>resulting histogram so that I get a smooth tonal gradation and no >>posterization. >> >>Is there any way of accomplishing this? > >Well, sort of. Here's one way: > >1. select the area that you want to affect using the lasso tool > >2. Do select->feather selection with a radius of 50-200 pixels >depending on how gradual you want the edges of the effect to be > >3. Layer -> add adjustment layer -> curves (or levels). This will add >an adjustment layer correctly masked so that only the bit of image you >selected is adjusted. > >4. Monkey with the tonality and apply the changes > >5. If you suffer posterization there is really no way to smooth it >out again without losing detail. The solution is to convert to (or work >in) 16-bit mode, which means rather than using an adjustment layer you >have to skip step 3 and apply the changes using levels or curves directly. > >There is another way of doing this which is more subtle: > >1. Roughly select the area you are interested in > >2. Apply tonal changes with the levels or curves tool (don't worry >about the sharp edge that results, we'll fix that). > >3. Click on the previous state in the history palette, which reverses >your changes > >4. Click on the little box next to the modified state in the history >palette to set this as the source for the history brush > >5. Use the History Brush to paint in your tonal changes. Use 25-50% >opacity and an airbrush or something similar. This is a very powerful >technique. You are painting with a FUTURE state, so the 'history' brush is >a bit of a misnomer, but hey. > >>I suspect there is -- because I've noticed something else >>interesting. I've taken to do a quick preview of my scans using >>"Preview" (the Apple application bundled with OS X). It manages to do >>something remarkable: When you first load an image, it looks grainy and >>harsh, with semi-posterized areas. But after about a second of >>calculations, it smooths out the tonal transitions, seemingly without >>loosing detail. The result is something that looks a hell of a lot more >>photographic than it did originally. Since this is step two of the >>process outlined above -- and something that I'd love to be able to do in >>PS -- how is it accomplished? > >This is just anti-aliasing (in Preview's preferences there is the option >to turn it on or off). The nearest thing in Photoshop is a Gaussian Blur >with a very small radius of say 1-2 pixels. It actually destroys fine >detail but removes jaggies in things like rendered text. > >Hope this helps. >-- >John Brownlow > >http://www.pinkheadedbug.com > >-- >To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html