Digital Tri-Color Photography with free Photoshop action

An old technique has a new lease on life in the digital world of Photoshop to create interesting images from both compact digital cameras and from dSLRs.

Back in the dark ages when I shot film ūüôā I used a creative technique called tri-color photography. In this technique I would set my camera, then a wonderful Canon T90, into multiple exposure mode, mount a Cokin filter holder and then, with the camera on a good tripod, shoot three exposures onto the same frame, one through a strong red filter, one through a green and one through a blue. The resulting transparency (that’s what I normally shot) would show a roughly naturally colored image of anything that did not move but wonderful color effects on subjects in motion. The technique worked well but it was not without its issues. Even with the Cokin filter system there was a risk of moving the camera or adjusting the lens zoom or focus while changing filters. Also, whilst in theory the three filters should have given a result in natural color, there were the inevitable differences between the exact exposure required through the three filters so that the result always had a color cast, though sometimes a small one. But the technique worked and I got some lovely images, especially of the sea, that I exhibited as large Cibachromes.

Now that I work digitally this technique is even easier. Digital cameras have the red, green and blue filters built in, but few have the ability to take multiple exposures. Thankfully there is no need for it.

Tri-color digital photography tutorial

Digitally, the tri-color process consists of the following steps:

  • Mount the camera on a sturdy tripod and either use a cable release or the self-timer;
  • Take three shots of a scene with some part of it moving;
  • Open the three images in Photoshop, Paint Shop Pro or similar software;
  • Copy the green channel from the second image and paste it into the green channel of the first image;
  • Copy the blue channel from the third image and paste it into the blue channel of the first image;
  • This gives you a composite image with the red channel of the first, green of the second and blue of the third.

Tri-color digital photography tutorial

You want to time the shooting so there is opportunity for movement to occur between shots. General with things like the ocean or trees on a windy day you can just shoot. With clouds moving you may want to give more time between shots.

Here is the step by step in Photoshop:
1.    Open three images in Photoshop. Select the first one;
Tri-color digital photography tutorial

2.    Do a Select All
Tri-color digital photography tutorial

3.    Activate the Channels palette and click on the Green channel
Tri-color digital photography tutorial

4.    Switch to the second file and select its Green channel
Tri-color digital photography tutorial

5.    Select All and copy the channel to the clipboard
5

6.    Switch back to the first file and paste the clipboard into the Green channel
Tri-color digital photography tutorial

7.    Select the Blue channel
Tri-color digital photography tutorial

8.    Switch to the third file, Select All and select the Blue channel
Tri-color digital photography tutorial

9.    Copy the Blue channel to the clipboard
Tri-color digital photography tutorial
10.    Switch back to the first file and Paste the clipboard into the Blue channel
Tri-color digital photography tutorial

11.    Click on the RGB channel to see the result
Tri-color digital photography tutorial
12.    The result after a mild sharpen
Tri-color digital photography tutorial

Tri-color digital photography tutorial

Tri-color digital photography tutorial
Tri-color digital photography tutorial

I have provided a free Photoshop Action for the Tri-color Process (you may need to right click the link and Save As) that you can download to your computer and use to do the above. You must open the three images first and have the first image the active one before playing the action.

Tri-color digital photography tutorial

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The above is, if you like, the classic approach. There are lots of variations you can make.

Tri-color digital photography tutorial

For example, if you shoot infrared, as I do, you can do a slightly different sequence:
1.    Open the three IR images
2.    Select the first image, do Select All and then select the Green channel
3.    Switch to the second image, click on the Red channel, do Select All and Copy
4.    Switch back to the first image and Paste the Red channel from the second image into the Green channel of the first
5.    Select the Blue channel
6.    Switch to the third file, select the Red channel, do Select All and Copy
7.    Switch back to the first file and Paste the Red channel from the third image into the Blue channel of the first.

Tri-color digital photography tutorial

Tri-color digital photography tutorial using infrared images

Tri-color digital photography tutorial using infrared images

You can, of course combine the green channels, in which case you move the channels into the middle file, moving the Green from the 1st into the Red of the 2nd and the Green of the 3rd into the Blue of the 2nd.

Tri-color digital photography tutorial using infrared images

Tri-color digital photography tutorial using infrared images

Tri-color digital photography tutorial using infrared images

Tri-color digital photography tutorial using infrared images

Remember, the resulting image is just a starting point for further work. You can swap the channels around till you get the color effects you want, do individual adjustments on the channels, apply blur or sharpen and so much more.

These tri-color processes work and work well. Some subjects work better than others, as is true of any technique. The results can be subtle if the movement is slight or bold if the movement is substantial, and particularly so with long exposures where the movements have blurred.

Give it a try, you just might like it.

Photoshop CS4 and Extended Depth of Field

An interesting feature of the latest version of Photoshop is the ability to use the alignment and merge capabilities that Photoshop uses for panoramas and HDR to extend the depth of field of your images. We look at how it stacks up.
We are still coming to terms with the features in Photoshop CS4, and indeed in the rest of the suite. One that intrigued us was the ability to extend the depth of field of your images. So we decided to make this the feature we would have our first deep look at.

Extended DOF makes use of the image align and merger capabilities that are well used for panoramas and HDR imaging. In this use you load up a series of images taken with different points of focus into layers and then do an align and then a merge.

The key to success with this approach is to make sure that each image has a substantial overlap of sharpness with both the image before it and the one after.

Photoshop CS4 Extended Depth of Field

Let us start off with an ideal subject and then get more complex.

This is what can happen when you have too few images without any or enough overlap of sharp zones.

Photoshop CS4 Extended Depth of Field

Step by step, this what you do:
1. Select the images in Bridge and go Tools-> Photoshop ->Load Files into Photoshop Layers

Photoshop CS4 Extended Depth of Field

2. In Photoshop, select all layers

Photoshop CS4 Extended Depth of Field

3. Do Edit -> Auto Align Layers

Photoshop CS4 Extended Depth of Field

4. Do Edit ->Auto-Blend Layers being sure to select Stack Images and Seamless Tones and Colors options

Photoshop CS4 Extended Depth of Field

5. All done

If you start with a series like this
Photoshop CS4 Extended Depth of Field
you end up with this
Photoshop CS4 Extended Depth of Field

Now the above is an almost ideal test, with a smooth, continuous distance change up the image. It is now time to look at some more challenging situations.

General Photography

Here is an obvious situation to try this technique. Even at f32, with our 100mm lens and the camera position we are using, we can’t get it all sharp, from the back of the chair in front to the distant window.

Photoshop CS4 Extended Depth of Field

So I took three shots, the one above, one nicely focused on the vase and beyond and one on the more distant door and window. Put together in Photoshop we get the result below, a completely effective result.

Photoshop CS4 Extended Depth of Field

Photoshop CS4 Extended Depth of Field

You can see the three layers with the resulting mask.

There are some possible side effects of this process. If you have dust on the sensor then since the perspective changes slightly as you focus, when the software does the alignment you can get a sequence of dust marks, as you have in the detail below.

Photoshop CS4 Extended Depth of Field

Another artefact can be found if you resize and then flatten, as opposed to flattening the layers and then resizing. This can be seen in the image below and seems to come about because of the way the mask is generated. Rather than when a top layer covers an area just leaving that area on the layer below, which is what you might do if doing this process manually (yes it can be done manually), Photoshop breaks the whole image up into a jigsaw puzzle of pieces across the layers. At least in the beta I am writing this from there seems to be a slight issue in resizing between the masks and the image parts themselves that produces this slight halo around the edges. We will see if it is fixed in the shipping version. But you can avoid it anyway by flattening before resizing.

Photoshop CS4 Extended Depth of Field

So, provided you have a small number of images and a lot of sharp overlap from image to image, it works. But what about on something really tough?

Macro

When I first saw this feature I immediately thought about applications in macro photography.

Below we have an image of amber I shot at f16.

Photoshop CS4 Extended Depth of Field

Here are a couple of 100% sections:

Photoshop CS4 Extended Depth of Field

Photoshop CS4 Extended Depth of Field

So I wanted to see if I could get sharpness through more of the depth of the amber. I shot 11 images, slowly moving the focus deeper into the amber. The result is below

Photoshop CS4 Extended Depth of Field

Below are two 100% sections:

Photoshop CS4 Extended Depth of Field

Photoshop CS4 Extended Depth of Field

This clearly did not work but I made it really hard on the software, using f4 for the individual shots.

For this new series of images I used f5.6, still a tough test.

Photoshop CS4 Extended Depth of Field

The result is excellent from combining the 20 images is excellent. I allowed even more sharp overlap from image to image.

Photoshop CS4 Extended Depth of Field “http://www.dimagemaker.com/ktml2/images/uploads/cs4/dof/20.jpg?0.09800907060671438″ align=”” border=”0″ height=”433″ hspace=”0″ vspace=”0″ width=”650″>

This shell fossil (below) worked extremely well from 10 images.

Photoshop CS4 Extended Depth of Field

One interesting thing with it, though, is that we can see in the 100% section below that specular highlights are not handled so well.

Photoshop CS4 Extended Depth of Field

Lastly I decided to revisit the amber. The shot below was taken at f16. Below that are several 100% detail areas.

Photoshop CS4 Extended Depth of Field

Photoshop CS4 Extended Depth of Field

Photoshop CS4 Extended Depth of Field

Photoshop CS4 Extended Depth of Field

By combining seven such shots taken at f16 we get the image below and then the 100% sections below that. By the way, the color of the amber was removed by the auto white balance of the camera.

Photoshop CS4 Extended Depth of Field

Photoshop CS4 Extended Depth of Field

Photoshop CS4 Extended Depth of Field

Photoshop CS4 Extended Depth of Field

This worked much better than the first attempt, but is still not perfect.

So what I think about this new feature of Photoshop CS4 is that it does, in fact, work. Yes you do need to be careful using it and the larger the inherent depth of field of the images it works with the better. It also does not work on all images. I also have come to the conclusion that the fewer images to be merged the better, which also works in favour of getting the greatest depth of field you can in each image. What this means is that you can shoot at the sharpest aperture, rather than the one that gives you the greatest depth of field, and then combine several images to end up with a greater depth of field than the smallest aperture will give you with a sharper result by avoiding diffraction effects.

It does take practice and it is not a rescue for bad photography in the first place, but it is a useful extension and another good example of computational photography offering real advances.

Once I have the shipping version of the software I will check to see if its performance has improved .

After the Shoot, Part 2: Basic Image Adjustment in Adobe Camera RAW

This ongoing series of articles covers what do you do after you have taken the picture with your digital camera. In this part we examine the basics of working with Adobe Camera RAW.
For many photographers Adobe Camera RAW is an essential part of their workflow if they shoot RAW and use Photoshop. Let’s look at one way (there are so many) to work with ACR.

I typically open my images into ACR from Bridge, using it to browse images in a folder to determine what I want to work on.  If you double-click on a thumbnail of a RAW file (NEF, CR2, etc) or right-click and choose Open in Photoshop it will come up in ACR for you to adjust before it gets passed to Photoshop.

Adobe Camera RAW

The Workflow Options (middle bottom link) allow you to control how the image will be passed to Photoshop. You can choose 8 or 16 bit per channel, pixels per inch and the resolution of the image. Setting the PPI here saves you one step and changing the size of the image likewise.

Adobe Camera RAW

Adobe camera RAW resizing an image
At top left you have a pretty full set of manipulation tools. From left to right these are:

  • Zoom
  • Pan around
  • White balance tool
  • Color sampler point tool
  • Crop
  • Level (to level horizons, etc
  • Red eye removal
  • Preferences
  • Rotate anti clockwise 90 degrees
  • Rotate clockwise 90 degrees

How you use these will very much depend on you individual photography and the way you like to work in Photoshop itself.  For me I like the Level, Crop and Red eye tools. I prefer to do other work, like retouching, in Photoshop.

To the immediate left of the histogram are the preview toggle and the full screen mode toggle. Working in full screen mode is generally useful in ACR. The preview toggle is extremely useful in judging whether your adjustments are improving the image or not. I will often toggle the adjustments on and off to see if I am improving the image or not.

In the top corners of the histogram are the highlight and shadow clipping toggles. You use these to turn the highlighting in the preview window of highlight and shadow clipping warnings. When on, highlight clipping is shown in red and shadow clipping in blue. I always leave these on.

Beneath the histogram is a tabbed panel that offers:

  • Basic
  • Tone Curve
  • Detail
  • HSL/Greyscale
  • Split toning
  • Lens corrections
  • Camera calibration
  • Presets

panels for a variety of options.

Now we come to the basic adjustments. It is rare for me to use more than the Basic tab in ACR as I prefer to do the rest in Photoshop, but we will cover those later. The histogram and the preview of the image serve as your guide here. You may wish to go to full screen mode to get as large a preview as possible; it does help. The Basic panel is effectively divided into three sections: basic color, exposure and color enhancement.

The top section is used to adjust the white balance from what the camera gave you. There are preset values accessed from the drop down menu that defaults to As Shot, you can manually adjust the two sliders or you can use the white balance tool to select a neutral part of the image. All three approaches are valid: you just need to work with the one or combination that gives you the image you want. Remember that is most photography color balance is quite a subjective thing. Some will like an image warmer, some cooler. Where it becomes a particular issue is in product photography and, to a less extent, portraiture (where some personal interpretation is usually fine).

The predefined settings, such as daylight or tungsten will roughly correspond to these options on your camera and I find server as a good starting point that gets me close to what I am after. Likewise the white balance tool, if you have a nice, neutral area in the image, will also get you close. Further adjustment can be made with the sliders.

Temperature effectively moves you between warm and cool. Tint adjusts the image along a green-magenta axis. Between the two you can tweak the image exactly.

My approach is to use either the white balance tool (when there is a neutral point in the image) or the presets to get me close to a neutral color balance. Then I use the sliders to bump it as desired. Generally I find this mostly entails just the Temperature slider to give an overall warmer or cooler balance to the image. Localized warming and cooling I do in Photoshop.
Adobe Camera RAW

In the case of this image the color temperature is probably about right for how it actually looked. We could warm the image up a little bit though by choosing Shadow.
Adobe Camera RAW

With this image of my wife and myself, shot by our daughter, using the White Balance tool on the black jacket is all that is needed.
Adobe Camera RAW

After white balance, getting the exposure adjusted is the next step. As you can see in this image, the default settings leave large areas of over exposed highlights but the histogram is pretty right in shape and coverage.
Adobe Camera RAW

Clicking Auto goes a long way to improving the image, and is always something I try to see whether the Default or Auto setting gives me the best starting point. In fact I toggle back and forth between these to see how ACR would evaluate the image.
Adobe Camera RAW

The six exposure-related sliders work in interesting combinations of ways.

Exposure moves the entire histogram up or down. I use it to set my white point, in other words to set the brightest part of the image.
Adobe Camera RAW

Recovery allows you to recover blocked up highlights without moving the rest of the histogram too far down the exposure range.
Adobe Camera RAW

Fill Light is Recovery for the shadows and, like Recovery, won’t tend to burn out your highlights.
Adobe Camera RAW

Blacks is used to set your black point.
Adobe Camera RAW

My approach is to use Exposure to set the white point, then Black to set the black point and then use Recovery or Fill Light if I need to get back detail in any of these areas.

Brightness acts like the Gamma (middle) slider on the Photoshop
Levels control and Contrast increases the steepness of the tone curve in the mid tones. I rarely use these, though I sometimes use Brightness when I need more than I can get with Exposure. Instead of contrast I prefer to use the Tone Curve.

All of the above you can do in Photoshop, if you prefer. It is largely a personal decision about how much you do in ACR and how much in PS. I tend to do this in ACR as it means I have the best image I can going into PS and then can concentrate on local adjustments.

Next article in the series: RAW vs. JPEG

The first article was: Import

After the Shoot, Part 1: Import

This ongoing series of articles covers what do you do after you have taken the picture with your digital camera.
When it comes to digital workflows, taking the picture is only the start of so many options. In this series of articles we will explore the options. So we can make some headway with a huge topic, we will assume you are using a fairly recent digital camera and that your interest in photography is a pretty serious one. Over this series we will cover a range of workflow options, including ones using Photoshop, Lightroom and Aperture, as well as other special purpose software and plug-ins to handle things like noise.

When I return from a shoot I have three initial priorities: download, backup and quick scan.

You would think downloading your images is an easy process but there are even a good number of options here. Firstly you can download from the camera just using a suitable USB cable or you can remove the memory card and use a card reader of some description. The first is simple, the second is much better if you use a lot of cards during a shoot (as I typically do) and want the fastest download. I’ve found many cameras can be positively slow when downloading directly, though this is far from true of all cameras.

After the Shoot Lexar
Also if you have UDMA compatible memory cards and a UDMA card reader (see B&H Photo UDMA products ) you will get much faster downloads than most cameras will do.

Also part of the downloading question is what software will you use? You can use the operating system and drag and from the files from memory card or camera to somewhere on your computer. When doing this, the camera’s USB mode needs to be set so that it just looks like a disk to the computer. You can use the software that came with your computer (such as iPhoto on a Mac), the software that came with your camera or some other program, such as Lightroom or Aperture. There are subtle differences between these approaches. When you use the operating system you have total control over where the photos go but then need a second step to import them into whatever program you are managing them in, such as Lightroom. Using software to import them and catalog them makes it one step but, depending on the program, many not give you all the control you want.

Making an immediate backup of your images should be the next step because in the process of importing them you may have cleared them off your memory card(s) and so only have one copy of the images. You can immediately backup to CD or DVD. You can backup immediately to a second hard disk drive, either attached to your computer or to the local network. Eventually you should do both. I backup across three disk drives, my computer plus two external drives. I then backup to DVD later at a convenient time. Please note that disk drives do fail. Do not listen to manufacturer’s hyp, drives fail and unless a unit is a suitable RAID system that provides redundancy to survive a drive failure, even a drive labeled as a backup drive is a risk. So you always need your images on at least two disk drives, and, as soon as you can, backed up on DVD and stored away from the computer (in case of fire or theft) as well. When you backup to DVD you should have a system in place so that you can find the right disk. This can be software based, by using something like Extensis Portfolio, or as simple as a log book. Just make sure you have a system that you use.

After the Shoot: Bridge

Giving your images a quick scan to see how they look is usually an urgent need for a photographer. You can use the software you used to import the images, the operating system (sometimes) or another program, such as Adobe Bridge. Remember that some programs will build their previews and save them, while others will generate them every time you open the directory. This affects your revisit time. Of course, those that save the previews use up more disk space but unless you are on a laptop this should not be much of an issue.

After the Shoot Apple Aperture

After the Shoot Adobe Lightroom

Next article in the series: Basic image adjustment in Adobe Camera RAW.

Digital Art Pioneer Releases Photoshop Brush Series

Laurence Gartel is a pioneer in digital art. In an exclusive we announce the debut of digital media artist Laurence Gartel’s Collection of Photoshop Brushes Volume 1: Automobiles.
Exclusive

Laurence Gartel has been doing digital art since its early days and has exibited widely.

Now he is branching out into supporting other digital artists, photographers and designers with a new line of Photoshop brushes. Presented by Karen Sperling’s Artistry web site, the 12 brushes represent Gartel’s artistic look at cars from past and present.

“I always had a love and fascination for cars, and felt that they were missing from the graphics world,” said Gartel, whose work has been exhibited in galleries and museums internationally, including in the permanent collections of the Smithsonian and the Victoria and Albert Museum.

“I always thought cars were moving objects of art.”

The 12 whimsical automobile brushes, which are compatible with recent versions of Adobe Photoshop and Adobe Photoshop Elements, are perfect for use with photographs, paintings, graphic design and scrapbooking.

To view the brushes and to order, visit the Artistry web site:

http://www.artistrymag.com/docs/brushes.html

or email Karen Sperling at [email protected]

Canon 40D Infrared Photography Tests

We test the 40D with a Hoya R72 filter for infrared capability.
The Canon 40D (available from B&H Photo) is an impressive camera. But how does it handle infrared photography? For these tests we used a Hoya R72 filter on the camera and mounted it on a solid tripod and used a cable release.

The resulting images show that the 40D is capable of great IR photography provided you are in no hurry.

Infrared photography with the Canon 40D

Infrared photography with the Canon 40D
This is how the image looks straight from the camera. The exposure was 100ISO, f4 and 30 seconds

Infrared photography with the Canon 40D
The original image

An optimized image converted from the red channel:
Infrared photography with the Canon 40D

From the green:
Infrared photography with the Canon 40D

From the blue:
Infrared photography with the Canon 40D

As you can see, image quality can be excellent.

Infrared photography with the Canon 40D
This image was taken with an exposure of 30 seconds and f4 at 100ISO.

Infrared photography with the Canon 40D
At this exposure the red channel is over exposed.

Infrared photography with the Canon 40D
The green channel is somewhat under exposed.

Infrared photography with the Canon 40D
As is the blue channel.

And for an examination of image noise. The first image in each pair is the straight image, the second is the green channel.

100ISO
Infrared photography with the Canon 40D

Infrared photography with the Canon 40D

200ISO
Infrared photography with the Canon 40D

Infrared photography with the Canon 40D

400ISO
Infrared photography with the Canon 40D

Infrared photography with the Canon 40D

800ISO
Infrared photography with the Canon 40D

Infrared photography with the Canon 40D

1600ISO
Infrared photography with the Canon 40D

Infrared photography with the Canon 40D

As you can see, the 40D is a very capable infrared camera.

Localized Image Enhancements in Photoshop, Part 4

I have always liked to modify small sections of images to enhance the overall balance. In this article we look at how to do this in Photoshop.
View part 3 of this series.

I decided to add this 4th part to illustrate more subtle effects (though still exaggerated a little so you can see in whatever web browser you are using). This image was shot last week when I was up in Sydney for an Autodesk press event and had some spare time before my flight home.

The straight image is not bad, but the sky lacks some drama and the opera house is a little flat.
Localized Image Enhancements in Photoshop

With a Levels adjustment layer I can enhance the drama in the sky, but it makes the rest too dark.
Localized Image Enhancements in Photoshop

A simple gradient gets us a long way towards mixing the dramatic sky with the straight ground.
Localized Image Enhancements in Photoshop

Painting by hand with a 5% opacity brush lets me bring some of the sky contrast down into the area near the tree and removing the straight transition.
Localized Image Enhancements in Photoshop

Now to the contrast in the opera house. I’ve added a brightness/contrast adjustment layer above the other and bumped the contrast for the opera house, though I have gone further than I want.
Localized Image Enhancements in Photoshop

Because I only want to apply the extra contrast to a small area, the first thing is to fill the mask with black to it is NOT applying to any of the image.
Localized Image Enhancements in Photoshop

Now I can paint back in with white at about 5% opacity and slowly buildup the contrast in the areas I choose.
Localized Image Enhancements in Photoshop

The end result has the drama I saw when I was there.
Localized Image Enhancements in Photoshop

Localized Image Enhancements in Photoshop, Part 3

I have always liked to modify small sections of images to enhance the overall balance. In this article we look at how to do this in Photoshop.
Go back to Part 2.

Another Infrared

Here we minimize the steps as I think you will have the hang of it now from the above.
Our starting image is interesting but needs a bit of work. Doing a pretty extreme levels moves the sky, especially in the top right, where I want it. With the hard horizon I use the selection tools to select the entire bottom of the image from the horizon and fill with black, so I only have the extreme effect in the sky and distant land. I then paint in to the distant land area and across the foreground to unify the image and to get the tonal focus where I want.
In these examples I’ve stuck with just using Levels but all the other adjustments will be suitable for some image used in this way. I’ve also made the effects more extreme so they are easy to see. When you work on your own screens you can be much more subtle and still successfully use these techniques.

Localized Image Enhancements in Photoshop

Localized Image Enhancements in Photoshop

Localized Image Enhancements in Photoshop

Localized Image Enhancements in Photoshop

I hope from this three part series that you have gained an understanding of how to move beyond enhancements to the whole image to crafting you image piece by piece.

View part 4 of this series of articles.

Localized Image Enhancements in Photoshop, Part 2

I have always liked to modify small sections of images to enhance the overall balance. In this article we look at how to do this in Photoshop.
Go back to Part 1.

Infrared
This is our starting image. It was shot in shade and is quite low contrast.
Localized Image Enhancements in Photoshop

Applying Levels is a standard thing I normally do to IR images. Now the trouble is, as I move the black point control around, I find different settings work best for different parts of the image. So I am going to need to apply different adjustments across the image.
Localized Image Enhancements in Photoshop

So the first thing is to apply the Layers -> New Adjustment Layer -> Levels.
Localized Image Enhancements in Photoshop

Just in case you end up working with multiple layers, choose the Use previous layer checkbox so what you do will only apply to this layer.
Localized Image Enhancements in Photoshop

Set the Levels to the most extreme change you want in the image
Localized Image Enhancements in Photoshop

In the Layers palette you will now see a Levels adjustment layer with its own layer mask filled with white. Remember that in layer masks white means the layer or effect is shown in full, black means it is not shown and shades of grey apply it partly in proportion.
Localized Image Enhancements in Photoshop

If we now put a white to black gradient in the mask we can vary the effect from none to full. With this image it doesn’t work because the effects need to be much more local.
Localized Image Enhancements in Photoshop

For this image better is to paint into the mask. Fill the mask with white, select black and the paintbrush tool. Pick a suitable size soft brush and a low opacity so that you can reduce the effect strength you want bit by bit. Note that with an image where you only want the effect in a few places it is better to fill the mask with black and then paint in the white where you need it.
Localized Image Enhancements in Photoshop

After painting for some time, correcting when you overdo it by painting in the opposite color, we end up with a satisfactory solution. Notice the mask contains areas of grey.
Localized Image Enhancements in Photoshop

Go on to Part 3.

Localized Image Enhancements in Photoshop, Part 1

I have always liked to modify small sections of images to enhance the overall balance. In this article we look at how to do this in Photoshop.
I find it is rare that the best I can get out of an image comes from simple, overall adjustments. Most images benefit from some degree of localized treatment. So in this article I offer you my way of working on images. We will go through three images, two infrared and one color.

Color
This is our starting image. The foreground is not bad but the sky and maybe the sea is weak. For this I’ve picked a clearly over exposed image that, perhaps because it is the only shot we have of a place, we want to rescue. In reality I would probably drop in another sky.
Localized Image Enhancements in Photoshop

Applying Levels is a standard thing I normally do to start with most images to adjust the black and white points. In this case we already have lots of data close to black and white. Adjusting the mid grey control is similar to adjusting the curve. Pushing it right up towards the white point makes the sky and sea stunning, but is not good to the foreground.
Localized Image Enhancements in Photoshop

So the first thing is to apply the Layers -> New Adjustment Layer -> Levels.
Localized Image Enhancements in Photoshop

Just in case you end up working with multiple layers, choose the Use previous layer checkbox so what you do will only apply to this layer.
Localized Image Enhancements in Photoshop

Set the Levels to the most extreme change you want in the image.
Localized Image Enhancements in Photoshop

In the Layers palette you will now see a Levels adjustment layer with its own layer mask filled with white. Remember that in layer masks white means the layer or effect is shown in full, black means it is not shown and shades of grey apply it partly in proportion.
Localized Image Enhancements in Photoshop

If we now put a white to black gradient in the mask (use the gradient tool after clicking on the layer mask in the Layers palette) we can vary the effect from none to full. This gets us pretty close. You can apply the gradient several times until you get the angle and transition correct. It took about three goes to get this right.
Localized Image Enhancements in Photoshop

To then fix it up further choose the paintbrush, set a low brush opacity and a suitable sized soft brush. Select black.
Localized Image Enhancements in Photoshop

Now paint into the mask, building up layers of paint where you need it to reduce the effect as needed. Zoom in and out, change the brush size and switch from black to white and back, as needed until you get what you need. You can see in the mask where we have made changes to the straight gradient.
Localized Image Enhancements in Photoshop

The edge areas can be fine tuned beyond this just by painting into the mask with smaller brushes.
Localized Image Enhancements in Photoshop

Further adjustments are always possible with this approach, as you have not changed the original image.
Localized Image Enhancements in Photoshop

Continue with Part 2.