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Source: http://www.tutorial9.net/tutorials/photoshop-tutorials/color-correction-basics-in-photoshop/#
Color Correction Basics in Photoshop
Have you wanted to learn more about color correction? The focus of this tutorial is to help you delve deeper into color correcting to up the production value of your images. Learn a few simple techniques while creating.
I will be using Photoshop CS4 for this tutorial, but all of the features I will use are available in previous versions of Photoshop. Or in any decent photo-editing software.
Primary Color Correction
In this tutorial, our work will be primary color correction. “Primary color correction affects the whole image, utilizing control over intensities of red, green, blue, gamma (mid tones), shadows (blacks) and highlights (whites).”
Overview
Before we begin, you’ll want to be sure that you have at least a novice understanding of the following tools in your photo-editing program: Curves, Hue/Saturation, Photo Filter, and Black & White adjustment layer.
Quick Tip
Keep effects on adjustment or separate layers to enable quick alteration or removal at any time during the color correction process.
Monochrome and Sepia
A monochromatic image is one whose range of colors consists of shades of a single color or hue.
Step 1: First, let’s make our image grayscale. There are various ways to do this, but we’ll look at just two:
I think the best way is to use the Black & White adjustment layer. (This can be found at the bottom of the Layers toolbox.) What is so great about this adjustment layer is the ability to control the luminance of the 6 primary and secondary colors – red, green, blue, cyan, magenta and yellow with the sliders. This is a very useful tool for fine-tuning the the tonal range of your image.
However, the Black & White adjustment layer is only in Photoshop CS3 and newer. So, if you’re using an older version, skip to the next step.
Step 2: Apply the Hue & Saturation adjustment layer. Click the Colorize checkbox and this will automatically desaturate and tint your image. However, the Hue is wrong. So set the Hue to 35. Now it’s starting to look right.
Step 3: Lastly, perfect color brightness of your image with the sliders in the Black & White adjustment layer. Use the eyedropper tool that comes with the filter to select the part of the image you want to alter and it will hightlight which color is in range. But be careful not to drastically change the colors or you’ll be in danger of posterizing the image.
Usually changes solely in the Black & White filter are not enough to correct the image; so apply a Curves adjustment layer on top and get your image looking right. (It’s best to do these steps last – after your color adjustments – so that you’re seeing and effecting the color-corrected spectrum.)
And, for sepia, you’re done.
Rollover Image
In addition, using other monochromatic color schemes are done the same way. Instead of setting the Hue to 35, move the slider to the color of your choice. You also could up the Saturation a bit to make the colors pop. (For the image below, I set the Hue to 295 and the Saturation to 35.)
Rollover Image
Bleach Bypass
A popular image treatment is the bleach bypass. In actual film-developing, this means skipping the bleaching process. This leaves a silver tint on the photograph, as if the black-and-white and color image had been combined. So that’s exactly what we’re going to do.
Step 1: Apply the Black & White adjustment layer once again to your image. (Or desaturate with a Hue & Saturation adjustment layer.) Then, the only alteration we need to do is in the blending mode: change it from Normal to Overlay.
Step 2: Apply a Curves adjustment layer on top. A characteristic of most bleach-bypassed images is increased contrast. So add a contrast curve to your image. But be careful. Adjustments should be minor at this stage because the image has a lot of contrast. Make sure you’re not overexposing in the highlights or underexposing in the shadows.
Rollover Image
Extra: Often, another characteristic of bleach bypass, along with increased contrast, is graininess. If you like, take this effect a step further by adding some noise: Filter > Noise > Add Noise. Make sure it’s monochromatic.
Quick Color Theory
Before we begin working on our next style, we’re going to talk quickly about color theory.
Take a look at the color wheels below. You’ll notice the three primary colors in our RGB color model: red, green and blue. Then, in between those you’ll notice the secondary colors of CMY: cyan, magenta, and yellow. Secondary colors are formed by the sum of two primary colors: cyan is green + blue, magenta is red + blue, and yellow is red + green. Simple enough.
The secondary colors are opposite on the color wheel to the primary colors. Hence:
Red – Cyan
Green – Magenta
Blue – Yellow
Another six tertiary colors are created by mixing primary and secondary colors. But we don’t need to get into that in detail right now.
The primary and secondary colors, and their relation to each other, are important for us to know. In the Curves adjustment layer you can effect color in the red, green, and blue channels separately. So, for instance, any adjustments upward of the diagonal line in the red channel increase the red in the image. Lowering, below the diagonal line, increases the cyan. The other channels are the same: Upward in the green channel, green; lower, magenta. Upward in the blue channel, blue; lower yellow.
Blockbuster/Fashion Look
Ok, now that we got that covered, let’s begin. This style is used a lot in big summer movies, such as the Transformer films. It’s also popular in fashion photography.
First off, take a look at the picture above. In an effort to create this look, determine the color hue and tint of the shadows, midtones, and highlights. Most importantly, the shadows and highlights. You’ll notice that the shadows are very bluish and the highlights – mainly the part of the image containing the skin tones – are, well, the color of skin.
This is a complementary color scheme. Meaning the colors used, blue and orange, are opposite each other on the color wheel.
When working with humans in your compositions, you have to take the skin tone into account. You can’t have people turning green, magenta, or blue. That would look odd. Skin will always be between orange, orange-yellow (tertiary), and yellow. Therefore to complement the subject, generally use opposite colors: between cyan, blue or blue-violet (tertiary).
Now that we know this, let’s stylize our photo.
Step 1: Apply a Curves adjustment layer to your image.
Quick Tip
Nearly every colorist starts color correction with the shadows; then the highlights; and lastly the midtones.
Step 2: In the color dropdown menu, change from RGB – which affects the overall brightness and contrast of the image – to blue. We’ll work backwards up the list, starting with blue and ending with RGB.
What we’ll want to do is bring the lower end of the curves slider up. This will increase the blue in the shadows. Next, to compensate for our first adjustment, we’ll want to decrease the blue in the highlights – taking it towards yellow – so that the skin tones stay closer to being correct.
Step 3: You’ll notice that the image has quite a purple tint to it. This is because the green and red channels are at equal intensity. To get a more blue color you can either go to the green channel and raise the shadows, or go to the red and lower the shadows. But there’s a difference here and you would do well to note it: If you were to raise the green shadows, the image would get slightly lighter and loses contrast. If you lower the red shadows, the image gets darker and gains contrast. The first is subtracting color and the second is adding.
In most cases, you’ll want to go with the option that subtracts, not adds.
And that’s what we’ll do. Go to the green channel, and bring it up just enough to take the purplish-tint out of the image. This is where you can decide between how much blue-violet or cyan you’d like in your blue-tinted shadows.
Step 4: At this point, you may need to go back to the blue channel and make sure the skin tone looks good. Not too blue and not too yellow. Adjust the highlights and midtones until you’re satisfied.
Step 5: Now we can go to the RGB or master channel. Finalize the luminance and contrast of your image. All I had to do with this image was lower the shadows.
I’m sitting pretty with a great look.
Step 6: Lastly, you can complement your image with one more filter. Increasing the blue in the shadows flooded the image with a bit too much color. Add a Hue & Saturation adjustment layer and drop the saturation to around -10.
The change is ever so slight. But, it’s perfection. And now you’ve got a blockbuster or fashion-style image. Smashing.
Rollover Image
Bronze
Like in the film, 300, you can give your image quite a cool bronze look. This is similar to a sepia effect; however, the image shouldn’t be monochrome. Vibrant colors and those opposite to the bronze tonal region are still visible and actually stand out nicely, while the lights and the darks take on the bronze tint.
Let’s use a picture with more colors and a larger tonal range. It’ll be easier to see what’s happening.
Step 1: Start by applying a Photo Filter adjustment layer to your image. Change the filter color to Sepia and set the density between 90 to 100 percent. Make sure the preserve luminosity box is checked.
Step 2: Add a Hue & Saturation adjustment layer next. Desaturate the image anywhere from -10 to -50. Do what looks good to you.
Step 3: Add that trusty Curves adjustment layer. The bronze-style looks quite good with extra contrast. Make a nice contrast curve.
Step 4: An optional step, one which I think looks good, is to add a little diffusion. You can achieve this by duplicating your image layer (and keeping it under the effects). Next, apply a gaussian blur to the layer. Do not blur too much! If you put too much blur, your final image will look like it’s from a dream sequence – very soft.
For this picture, I’m using a 2.5 pixel blur.
Change the blending mode of the blurred image to Overlay. You’ll notice how contrasty your image gets. To keep it from getting too soft, change the fill anywhere from 25 to 50 percent. Then, compensate for the contrast accordingly with your curves layer.
That’s it for the big, bold, bronze look. This kid is vicious on his scooter. Watch out.
Rollover Image
Conclusion
Bear in mind that there are many ways to achieve these looks and styles. There is no correct process or proceedure. Different colorists use different tools. To each his own. Find out what works best for you.
Also, remember that each picture you add these effects to will react differently. You shouldn’t expect these settings – or one specific procedure – to work equally well on all your pictures. It will vary due to the levels or amounts of shadows, highlights, colors, and contrast, etc.
The tendency can be to go overboard with effects. Do your best to use them sparingly and appropriately. When in doubt, less is more.
Go out and take your knowledge further by emulating styles and effects you see in magazines, films, or on the web. That’s a great way to learn. Have fun.
