 Correct globally for shark, and water becomes too magenta. Hue sliders allow for adjusting colours separately For my friends who are using Lightroom or ACDsee image processing software, you can adjust targeted colours using the Hue, Saturation and Luminance sliders! It helps to understand colour, so if you were not interested in colour theory in art class back in your highschool days, here is a little cheat sheet. Your camera captures the colours Red, Green, and Blue, and your monitor displays colour by emitting light through Red, Green, and Blue phosphors. ALL the colours you see on screen are created by mixing these three colours in varying intensities.  The colour wheel. The Colour Wheel Simply put, each colour on the wheel is created by mixing equal amounts of the colour on either side of it. For example, equal parts of Red light and Green light will result in YELLOW. Really! The colour directly opposite any colour on the wheel, represents its COMPLEMENTARY colour. If an image has a colour cast, you need to correctly identify the colour cast, and ADD its complimentary colour to neutralize it.  In the Lightroom slider panel, look to the left under the tab HUE. Click that double circle to click and drag colours directly on the photo. When we go diving, we notice significant colour loss in the scenery; Red, Orange, and Yellow light is filtered out of the water as we descend. This results in a very ugly colour cast that makes everything green or blue. If you have a colour cast of green (diving at the local lake), then you will want to adjust the white balance sliders by adding its complementary colour - Magenta. If the colour cast is Cyan, add Red. Sometimes colour correction of a subject or foreground results in undesirable colour in other parts of the photo, such as the shark picture at the top of this cheat sheet. The photo on the far left is direct from camera, the middle photo is the result of correcting colour for the shark (she was too green, so magenta/red was added), but this created a gross magenta colour cast in the water. It is so bad, that in the Hue slider, we adjust in the purple, sliding it to the left (toward blue), and blue to the left (toward cyan/green) to bring water back to blue.  What colour is your water? The BLUE Hue Slider: Slide left for more green (becomes Cyan). Slide right for more red (becomes magenta). The Hue, Saturation and Luminance sliders can be found in a panel together in Lightroom, Adobe Camera Raw, and ACDsee Pro and Ultimate.
Hue This is where understanding your colour wheel comes into play. Change specific colours by moving sliders left or right. This means that the blue background of an underwater image can be made greener or pinker. Keep an eye on the other colours of the photo to make sure nothing is going awry. If another aspect of the photo is being detrimentally changed at the same time, then you may need to make a more specific target by using adjustment brushes to paint an effect on only an area of your choice (that's a cheat sheet for another day). Saturation Increase or decrease the brilliance of a specific colour in the photo. Luminance Darken or lighten a specific colour in the photo. Watch the effect particularly around edges to make sure weird halos aren't being created. Happy Sliding!
2 Comments
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.  Colour Correction with Curves and LAB Colour Mode 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. Objective: We have decided to change this image of a blue and black jacket to a red and black jacket.  Original Jacket on the left. Top right, curves open for "a" channel. Bottom right, curves open for "b" channel. 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:  The curves display for both the "a" channel (top), and the "b" channel (bottom). 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  Original image of Honey comb trunkfish 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.  Adjustments to the Lightness channel only 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.  Adjusting Curves on the "a" channel 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.  Adjusting Curves on the "b" channel 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!  Final result 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  Notice the chromatic aberration along the arms. 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). Method 1 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.  Method 2 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:
The Steps
 This part of the process will be numbered to correspond with the figure below.
 Brush Options are circled at the top. Now just carefully "paint away" all that ugly!
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!  Before and After editing: Photo taken with a Sony A600 with Nauticam housing. 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.  5000x5000 pixels, 72 ppi, Background is set to black. Creating the File
It doesn't matter if the new file is RGB or Grayscale.  Create your selection with your image needs in mind. 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.  The "Sun Rays" look choppy.
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!  Sun rays left at full strength (I think I will soften the effect for my own use). |
 AuthorsJill Smith 
Coral Restoration
Archives
January 2024
Categories
All
 
|
RSS Feed
Our Services |
Company |
SupportOur Blog
|
|
Copyright © 2014
|
Newmarket, ON
|
(905) 898 5338
|