By Jill Smith
An Adobe Photoshop ® tutorial
This is a colour correcting technique that may be employed in Adobe Photoshop ® using the Curves contrast adjustment tool in conjunction with LAB colour mode. Convert an image to LAB colour mode, and apply curves to the channels individually to knock out extreme colour casts, boost colour and even make very specific changes to colours all in one fell swoop.
A LITTLE ABOUT CURVES:
The Curves dialogue box is another graph mapping all of the tonal values on a straight diagonal line. The steeper the curve, the more contrast between the tonal values in the steep part of the curve; the flatter the curve, the flatter the contrast in the tones of that area of the curve.
Click within the image, and a small circle will appear on the curve where that tonal value is represented. You can set a point on this line by clicking on the line directly, or by Ctrl-clicking within the image to plot that specific value on the line of the curve. Up to 14 control points can be added to the curve; this allows for very precise control when adjusting contrast. Each point may be edited separately.
A LITTLE ABOUT LAB COLOUR MODE:
LAB Colour mode consists of 3 channels much like RGB; however, the similarities end there.
The LAB channels:
First, let’s illustrate the concept of LAB with this jacket to help us understand using Curves with the LAB channels better.
We have decided to change this image of a blue and black jacket to a red and black jacket.
The image has been converted to LAB Colour Mode (Image > Mode > Lab Colour), and the Curves dialogue box is open - Image > Adjustments > Curves (Ctrl - M for PC /Command –M for Mac).
Note: Both of these Curves graphs plot the colour values along the diagonal line (top graph is for "a" channel, bottom graph is for "b" channel). Adjustments in a and b will affect colour, but not contrast.
About "a" channel curve: Values that are plotted on the mid-neutral line in the center are neutral (neither green nor magenta). Values plotted above the neutral line are more magenta than green, increasing in intensity the higher it goes. Conversely, values plotted below the mid line are more green than magenta.
About "b" channel curve: Values that are plotted on the mid-neutral line in the center are neutral (neither blue nor yellow). Values plotted above the neutral line are more yellow than blue, increasing in intensity the higher it goes. Conversely, values plotted below the mid line are more blue than yellow.
Top Right ("a" channel curve):
Above the graph display the Channel selection (drop-down box) has been changed from "Lightness" to "a" (I am satisfied with the brightness and contrast of this image, so I am not going to adjust curves on the Lightness channel).
The "a" channel contains all of the green and magenta colour information. There are two values plotted on the graph. The top one was selected by Ctrl-clicking (Command-clicking for Mac) a good representation of the black fabric around the shoulders and the neck (do not take the sample from either the highlights or the shadows). It is seen plotted on the mid-neutral line of the graph, meaning it is neither magenta nor green. The bottom value was plotted by Ctrl-clicking a good representation of the blue fabric (neither highlight nor shadow). This value is plotted well above the mid-neutral line, indicating there is more magenta than green in the colour of the jacket. The red arrow on the graph shows the direction we are going to take this value when we edit (next).
Bottom Right ("b" channel curve):
The bottom curve shows the graph for the "b" channel containing all of the blue and yellow colour information. Again, a value representing the black has been plotted on this graph-line by Ctrl-clicking a good representation of that tone in the image. This time, the value is not plotted exactly on the mid-neutral line, but a little bit below, indicating either a blue colour cast, or perhaps the true colour of the fabric is navy blue.
Below that (still see the figure above, the graph below the "a" graph), is another point that has been plotted on the line to represent the blue values in the jacket, and again, the red arrow on the graph illustrates the direction this value is going to be moved when we edit.
Editing the Value Points:
Now let's edit those points.
That's it, look Ma, no selections! This is an easy example, because the background is blank and relatively neutral, but it is a great image to introduce the concepts. Now let's colour correct an underwater image.
Applying Curves with LAB Colour Mode in an Underwater Image
I've never met an underwater image that didn't need some help, and this image can do with some pretty drastic adjustments in LAB. This Honeycomb Trunkfish and small yellow remora riding under him, is underexposed, and the colour cast is very cyan. At a glance, the water in the background looks like it has too much magenta in it too.
First step is to open the image and convert to LAB (Image > Mode > LAB colour). Then open Curves (Image > Adjustments > Curves, or Ctrl-M/Command M for keyboard shortcut). The default Channel selected is the Lightness channel. That is where we will start.
By clicking and dragging the cursor over the image it is possible to see where the values are plotted on the curve; note the lightest area of the image with detail (mouth of the trunkfish), and where that resides on the curve. Instead of Ctrl-clicking though, I click a value on the line above the lightness values of the mouth. This is because I want to keep the detail of mouth in the steepest part of the curve for contrast and detail (I don't count spectral highlights as important detail - there aren't any in this image anyway). The highlight point is dragged up significantly to lighten the image, and increase contrast, while watching the mouth area to make sure it isn't being clipped. To set the shadow, find the darkest values of the area of interest, and see where that value lives on the curve. Then manually click a point below that, and lower it to darken shadows and increase contrast.
The curve now has an "S" shape, and all of the values of the image that are important detail, reside in the steep part of the S, creating more contrast. At the extreme bottom and top of the S, the darkest shadows and the lightest highlights are actually flattened and have less contrast. It may be helpful to remember that when adjusting the curve for contrast, while one part of the curve is made steeper to increase it, another part of it will be flattened, decreasing it.
Above is the Curves adjustment for "a" channel (selected from the dropdown Channel menu):
For now, 3 points plotted is enough, although plotting a point for the sandy area roughly on the same plane as our fish would not be a bad idea either, but we'll check those values after we make some adjustments.
Clicking the water value, pull it straight down to the green. Push the Trunkfish's skin value to the neutral, and drag the remora's yellow value up towards yellow. At this point, check the sand value near the fish , and try to keep it close to neutral, or even slightly warm in the magenta, but not too much. The sand in the distance may retain some blue values, and that is acceptable because it is natural-looking. The colour still doesn't look right, and that is ok, because we haven't adjusted any colour in yellow/blue yet.
Above is the Curves adjustment for "b" channel (selected from the dropdown Channel menu):
The remora yellow may be raised a bit to make it a more intense yellow, but care must be taken to not introduce too much yellow to the sand. The sand may be a little yellow, but should not be as intense as our little remora. If the sand became too yellow, it may be plotted on the curve and pulled down a little. You have so much control here!
If sharpening is desired, sharpen on the Lightness channel before converting back to RGB to avoid colour distortion around edges. Then I do any minor tweaking in RGB, and I'm done!
I do love that I can control the colour and the intensity of a colour in an image using LAB and Curves; even two colours that are very similar may be pulled apart to be made more distinctive.
I hope you find this colour mode to be useful to you; it has become one of my favourite tools in more ways than one.
This is a pretty quick and dirty introduction to a very comprehensive colour mode/topic. Want to learn more? Here is a great resource written by one of my favourite instructors, Dan Margulis (now semi-retired):
Margulis, D.2006.Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace.California:Peachpit Press.
By Jill Smith
Chromatic Aberrations are those ugly, coloured halos that may outline contrasted edges in an image. They are often bright blues and yellows, or magentas and greens. The colours of light (yes, white light is made up of colours; all the colours of the rainbow - same principles apply), don't all behave and bend the same way. That is why we get to see and enjoy rainbows (nice), but also why we have these gross distortions (not so nice). Here are two quick and dirty ways to banish them (one way is quicker and dirtier than the other, but it may not always be the answer).
RAW images - If your images have been shot in RAW file format, they may be opened in Camera Raw, and possibly corrected very easily there. Go to the Lens Corrections tab, and click the “Remove Chromatic Aberration” box at the top of the panel. Most of the time this will do a good job. That was easy.
The following Chromatic Aberration Removal technique may be employed in the event that the Camera Raw feature did not completely remove the aberration, or if there is no RAW image to work with.
This image sports arguably the most grotesque chromatic aberration I have ever seen. Notice how the distortion becomes more severe further away from the centre of the image. The distortion here is so terrible for a couple of reasons:
This part of the process will be numbered to correspond with the figure below.
While the nasty colours have been taken care of, this particular image (and this section taken near the edge) was an extreme example, and I can still see the contrast on the edges. If I first ran this image through Camera Raw and checked the "Remove Chromatic Aberrations" box, they would have been largely removed, and the above method would have cleaned the rest up beautifully....but for this method, we wanted to work with the worst case scenario.
Happy Shooting and Editing!
I LOVE taking a good shot and making it look awesome!
Do pictures lie?
Maybe a little, but the original image of the shark above, on the left, was not the scene as it appeared to the human eye either. The truth is probably somewhere in the middle. Just as an artist can render a scene using any manner of techniques or styles: realism, pointillism, abstract, etc, I too, can express my creativity in my colour correction techniques, and even a few enhancement tricks. Like sun rays.
For the colour correction technique used on this female reef shark, go here...for creating rays of sun, read on...
"Sometimes a well placed ray of sun just makes the heart sing."
Want to know how to easily add rays of sunlight to your beautiful underwater shot? With a custom brush. Here's how:
I've chosen this shot of a sea turtle because there are already faint rays of sun streaking through the water behind him.
Most of my underwater shots would not be amenable to adding rays of sun, because a lot of my photography is shot in deeper water. This photo, however, was taken in shallow water, and there are very subtle streaks of sun rays shooting down behind the turtle, making this image a great candidate for adding or enhancing sun-ray effects, while maintaining a natural look.
Creating the File
It doesn't matter if the new file is RGB or Grayscale.
Creating a Brush Pattern
Select the Elliptical marquee (M) from the tool bar. Notice that I have created the selection near the top of the file, to give the rays I am creating lots of room to spread down. I have also created the elliptical selection quite wide, horizontally, in an effort to spread the rays across the image to some degree.
You may choose to create a perfect circle selection (hold the shift key down while dragging the elliptical marquee tool), if you require light rays coming from a smaller or more specific area, like light rays through a cave opening, for example.
Because the "sun rays" look a little choppy to me, I will run the radial blur a second time, using the exact same settings (this may be done easily by going to Filter, and clicking the function at the very top of the list. This spot is reserved for the last filter function used in Photoshop, with the settings saved). This time I have a much cleaner set of sun rays.
Creating the Brush
Now we are finally ready to create the brush.
Your brush should now be a part of your brush library. Create a new layer on top of your image, and test your brush. Choose the desired foreground colour (I use white). If the effect is too strong, remember that the opacity of the layer may be reduced to soften the effect.
Enjoy, and happy diving!
By Jill Smith
If you are taking pictures underwater, then you already know that no matter how great the shot is, it is going to need some work post-processing. It is an unfortunate truth that light does not travel through water as it does through air, so we have to deal with a severe loss of colour as the red (followed by orange and then yellow), gets filtered out inch by inch. The more water between you and your subject, the more the colour gets filtered out.
First of all, don't use Photoshop as an excuse to get sloppy with photography. Getting the best shot possible from the point of click, not only makes the post-processing easier, but the final result will be so much better!
How many divers are using Adobe Photoshop to colour correct their underwater photography? If not Photoshop or Lightroom, what do you use? Feel free to add comments below and share your experiences with us! If there is interest, I will keep posting some of the tips and techniques that work for me, and for anyone who wants to contribute, we can share your tips and successes too!
Do It In the RAW
No joke. My whole camera choice was based on the priority of my needs.
Priority number 1: I want to shoot in RAW. Why?
Priority number 2: I wanted to find a compact, mirrorless camera that had all the capabilities of a DSLR.
So, I decided to purchase the Sony A6000 mirrorless camera (already obsolete), and a Nauticam housing (new November 2016: 2.8 16mm wide angle lens with a dome port for my housing!).
Using Camera Raw
One method of underwater colour correction enhancement I use frequently is to open the RAW image in Camera Raw and make adjustments for the water, and ignore the subject matter entirely. Once the image exposed for water is open in Photoshop, I then re-open the RAW image in Camera Raw, and this time I make adjustments for the subject. Both versions are opened in Photoshop. This is purely subjective. I love the deep blue of the water, and I want to keep that.
In the image below, (opened in Camera Raw) I can see I am having a problem with the vignette shadows in the corners. I was aware of this problem when I got my Nauticam Housing for the Sony A6000, and simply forgot to tweak the zoom in a little bit to avoid that. That can be corrected or cropped out at the end.
Above is a map of the Camera Raw dialogue box (basic). Under the adjustment tabs there are sliders for making basic adjustments to the image:
Temperature and Tint - these are for adjusting white balance. I use these a lot for underwater images
Exposure - there is a little wiggle room here if the exposure is off. Exposure can be increased or decreased by up to 5 stops.
Contrast - Slide the contrast up or down
Highlights - may be nominally useful if you have strong highlights you wish to tone down.
Shadows - open up the shadows in an image they are too dark
Whites - adjusts white clipping (clip whites more or less)
Blacks - adjusts black clipping (clip blacks more or less)
Clarity - creates a super-contrast effect on mid-tones (similar to a large radius sharpen)
Vibrance - a kind of smart saturation tool; vibrance increases saturation of low saturated colours, but has less effect on colours already high in saturation.
Saturation - increases saturation of all colours equally
For those of you who like the second image and would not wish to do anything further, I used the white balance tool in Camera Raw to make the wetsuit neutral. You can find that in the top menu bar beside the hand tool. Click the dropper and then click an area in the image that you KNOW to be black or gray neutral; I used a part of my son's arm. I chose an area that was neither in shadow nor highlighted, just a good representation of the wetsuit.
Most of what you see there is a result of the white balance tool. I may have tweaked a few settings here and there, but not much. When you are satisfied with your adjustments, click "Open Image" (bottom right area of the dialogue box). Now there are two images open on the Adobe Photoshop desktop.
Select the move tool from the tool bar on the left side of the desktop. While holding the SHIFT key down, click on the image adjusted for the subject, and drag over to the image adjusted for the background. Let go of the mouse before you release the shift key.
If done correctly, you will have both images stacked together in one document, perfectly aligned (holding down the shift key while dragging the image over places it in the perfect centre). Confirm this by checking your layers palette on the left side of the desktop. With the layers tab highlighted (at the top of the palette), you should see two layers stacked underneath. You will only see the top layer in the image window. To ensure that they are aligned properly, turn the eyeball icon on and off of the top layer to show the layer underneath (eyeball icon is to the left of the thumbnail of the top layer in the Layers palette). If they are perfectly aligned, then we are ready to start working on our layer mask.
Make a Selection
Make a selection of everything but the subject, and mask out the background of the top layer - allowing the background of the bottom layer to show through. There are a few selection tools to choose from. Under the Move tool on the tool bar, there are 3 options for selections: Rectangular Marquee, Lasso, and Magic Wand. Further to that, there is a tiny triangle in the bottom left corner of each of those icons, meaning that there are more tool options underneath. Click and hold the icon to reveal the mini-menu.
I chose the Quick Selection tool, found under the Magic Wand. Click and drag to add pixels of similar colour and tonal value to the selection. The selection will show like a row of marching ants around your edges. If it adds too much, hold the alt key down (notice the little minus icon inside your cursor) and click and drag the tonal values you wish to subtract from the selection.
Create a Layer mask
Once the selection is done, go to the bottom of the Layers Palette and click the "add a mask" icon (or go to Menu > Layer > Layer Mask > Reveal Selection). The "add a mask icon is to the right of the fx icon and looks like a circle within a rectangle. Make sure your top layer is selected when you do so. Now we have a layer mask applied to the top layer based on our selection. The thumbnail to the right of the image thumbnail shows us what is masked in black to allow the underneath layer to show through.
While the Quick Selection Tool does a great job in areas where the edge contrast is very pronounced, there may be some areas that need "tweaking". We can simply use the paintbrush tool to brush the black in areas we wish to mask, and white in areas we wish to unmask.
To edit the mask, select it in the Layers Palette (you will see the highlight box surrounding it), and select your brush from the tool bar. Your foreground colours should be black and white, but to make sure they aren't any shade of gray, reset them by hitting the letter "D" on the keyboard. You will be painting on the mask with the foreground colour. If you wish to change from black to white (or back again), hit the "X" key on your keyboard.
Other Keyboard Shortcuts to help Edit Mask:
Increase or Decrease Brush Size: Square Brackets (beside P)
Zoom in: Hold the Spacebar and the Ctrl key as you click inside the image
Zoom out: Hold the Spacebar and the Alt key as you click inside the image
Navigating within a zoomed image: Hold Spacebar down and the hand tool will appear. Click and drag while continuing to hold the Spacebar down to navigate within a zoomed image.
You can make any adjustments you wish to either layer and they will remain separate.
Done! Flatten Image (Menu > Layer > Flatten Image).