Here's a tip on using the Shadow / Highlight feature of Photoshop. I'll describe my typical established workflow using this tool, in order to help others using it.
Shadow / Highlight is in a special category of tools, based on light zones in your image. You can use it to increase or decrease contrast, or indeed both in one go.
First of all, I wouldnt recommend using Shadow / Highlight on an 8-bit image. You can do it, and it will give you results in a pinch, but the image quality will be much better if you start out with a 16-bit image in a large color space.
When I come upon an image that I can see would benefit from Shadow / Highlight, I let that notion dominate how I treat the image from the start. I shoot RAW with a Canon 10D. The example we will examine is a tourist snapshot from Trafalgar Square, which I shot during an easter holiday. Now, the basic qualities of the shot is not the subject here. By all means it has a fair share of photographic problems beyond this subject, but we'll use it for the purpose of this demonstration.
It was a typical overcast rainy day in London, and I could see that this image deserved a contrast treatment. I could scuffle about in Camera Raw to try to get some contrast out of it, but instead I ignored all contrast enhancements in the RAW developer, only making sure that white balance were fairly accurate. All other settings were left on Auto (possible exclusions to the Auto rule is Contrast and Black Point sliders, as these are contrast modifiers). The rule of thumb is that all data must be comfortably inside the histogram, and less contrast is better than more contrast.
Bypassing contrast enhancements also means setting the Curve to linear, in order to maximise the data we can use later on.
I opened the photo in Photoshop in 16-bit ProPhotoRGB space. This is the largest space Camera RAW allows me to open my photos in.
Now, the first thing I want to do is to use S / H to increase the contrast of my image. Instead of launching the tool on a global basis, I much prefer to use a mask with the image, as this helps eliminate the halos created by S / H. This is easy to do. I just use a Luminosity mask, created by Ctrl-clicking the composite RGB channel in the channel palette. This will create a selection based on the brightness in the image. That is, the lighter parts are more selected than the darker parts. This pre-operation is in itself a zone mapper of sorts. It will mean that whatever you do in S / H, you will have to keep in mind that the lighter parts will be much more effected than the darker parts.
Next, I launch S / H and experiment with the settings. Immediately I discover that the sky is brightened, not darkened. This is due to the clipping settings, as my image histogram does not reach all the way to the right. This is OK, though; I want to end up with a maximized histogram.
I start out setting the default shadow amount to 0, instead tweaking the highlight slider, keeping the Tonal Width at the default 50%. As the sky was lightened by the highlight clipping, it takes a drastic Amount to get the sky down to the level I want it. To avoid halos, the Radius is set at 90, which I find to be a reasonable setting for a 6MP image (70-120). The combination of contrast introduced cia clipping settings and the highlight suppresion slider leaves me with a much more dramatic, contrasty sky. The fountain really pops out against the sky now, compared to before.
Next, I set the Shadow Amount to a reasonable setting. This also takes a drastic measure, as we are using a selection based on lighter parts. Radius again set to 90.
Finally, I increase the Color Correction slider to a massive +60. As we are in 16-bit ProPhotoRGB space, the dull and lifeless image can easily take the color injection. I left midtone contrast to 0. I still find that I can control midtone contrast better with a curve adjustment later on if I wish.
Exiting my selection, a final tweak involves a final Levels or Curves adjustment to get perfect contrast and clipping.
My usual workflow involves a global Smart Sharpening at this stage, before converting down to my final or archival destination space and bit depth. I forgot to mention that I do not apply sharpening in my RAW developer (leave it at 0).
Here are some pitfalls to be aware of when using this tool:
1) Dont overdo it. As an imaging pro, I can always tell when shadow highlight has been overused, or used badly. This is especially obvious when it is (over-)used on an 8-bit image. If you want to seriously expand your image DR, investigate other options, such as developing several versions of your RAW image and merge them later, or Merge to HDR.
2) Avoid halos. At all cost. Simply do not accept visible halos. A luminosity mask helps a lot.
3) Use S / H in 16-bit ProPhotoRGB space for highest quality results.
I should note that my settings for S / H are a bit more extreme than usual for this particular image. That's because its so dull to start with. With highlights closer to the right of the histogram, much less Amount for highlights suffice.
- 6:49pm Apr 19, 06 PST
Thanks Mathias, I'll also give this a whirl, I'm not familiar with S/H at all at this point.
- 12:37pm Apr 20, 06 PST
You must be reading my mind, Mathias, as I was just wondering if you might come up with some information on your take with S/H.
My problem is the reverse: Too much contrast, and I work with scanned images, so I am not using raw. So, I have set up default S/H thusly:
As you can see, it's for a greyscale, but for RGB I would be using the same settings, leaving contrast and color set to Adobe defaults. This is my starting point, and for many of my images, all that is necessary. Once in a while, I throttle back with the Fade, but very seldom. If it isn't working, I tweak the controls, usually starting with the radius.
I haven't tried your selection mask yet. looks like a splendid suggestion, (as usual!).
On certain images with backlit clouds, I frequently set the highlight radius well above 100.
The most disturbing effects I have noted is the contrast enhancement around abrupt changes in picture elements, like a mountain against a cloud. The edge of the mountain goes dark and the corresponding edge of the cloud goes light. In analog work, this is known as the Eberhard effect, and is the principle problem with Tech Pan. Trying S/H on those negs is trying indeed!
- 2:59pm Apr 20, 06 PST
Try the luminosity mask. I think it will help the halos you see around contrasty subjects.
For scanning, you can still use the two develops method; Scan two versions into 16 bit with different exposure and merge them in Photoshop. Layer one version over the other, and use the luminosity mask from one layer as the layer mask on the other. The combination will be a bit flat, and will need some contrast. This is one situation where you can use S / H to add contrast.
There's nothing wrong with using S / H to decrease contrast, I think this is its primary intended use. But you have to live with the halos induced by a radius based contrast modifier. You dont have to live with halos using the combine method.
Using S / H with a luminosity mask is my own humble 'invention', but I see that it works well regarding controlling the halo effect. - to a limit. It also helps against accidentally lifing the shadows to much, exposing your use of S / H. Other masks could be used, I'd be very interested in other options or ideas people here might have.
- 11:09pm Apr 20, 06 PST
Hi again Mathias,
You have a real insight here. I gave it a try and the Luminosity mask is a jewel. But using it as you describe is only the beginning.
First off, I decided to look at which to use, straight or inverted. That extends the application several fold, as now we have two ways to apply tools. And by tools, I mean far more than S/H.
The next place I tried it was the procedure you call contrast coating (I call it brightup.) here is another place to get into trouble, and the Luminosity mask again proved it's worth. But wait! There's more! Sharpening! Use the mask when sharpening an image and with the right polarity selected, one can really sharpen a fuzzy image. I was able to apply sharpening on the order of an Amount of 300 and a Radius of 3. That decisively sharpened an image which could not be well sharpened without a huge halo problem.
What is actually affected? To decide this, I used Curves to watch what areas were responding. Inverting showed a completely different outcome for the same adjustment.
Most fun I've had since....:)?
- 6:44am Apr 21, 06 PST
"What is actually affected?"
You can create an alpha channel from the mask by hitting the Create Channel from selection icon in the channel palette. You can then not only see what areas are affected, but you can manipulate your alpha channel with curves to get just the selection you want. I like the straight highlight / midtone L mask, though.