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Colour By Numbers

An introduction to digital colour correction & grading
By Bradley Steenkamp

Though often overlooked by beginners, colour adjustments can do a lot for footage, from fixing incorrect camera settings to adding some Hollywood sheen.

Colour correction and grading are stages in the video‑making process that are easily underestimated in the face of all the other decisions involved in video creation. Most musicians and producers know how important mixing and mastering is to producing a song or album, and colour correction and grading is a bit like the mixing and mastering  stage: it's best not missed out! Throughout this article, I'm going to attempt to explain a little about the colour-correction and grading process and suggest some tools and techniques that will help you get the best out of your video footage.

Grades Of Grading

Colour grading is the umbrella term that is used to describe the final post-production stage during which the colour balance of footage is altered, processed and enhanced. The first step of the grading process is usually colour correction, which tends to refer to the process of fixing something, such as an incorrect white balance or exposure. In most cases, we would want to avoid having to colour-correct footage by just capturing it perfectly at source! However, sometimes images just don't look quite as they should, or a decision is made to shoot 'flat' with low sharpness, contrast and saturation (see 'Picture Profiles' box) in order to capture maximum detail before extending contrast in post production. In these cases, colour correction will be necessary. Almost all cameras allow the user to set a white balance with options that include settings such as Auto, Daylight, Cloudy, Tungsten and others. If you happen to select the incorrect setting, or find that the Auto setting doesn't quite get it right, the colours might appear to have a blue or red cast, for example. This tends to be most noticeable in areas of white. If an object in shot should look white but appears 'coloured', it may require some colour correction.

Once the colour correction is complete, we can move to the more artistic stage, and attempt to achieve a specific 'look'. High-budget TV programs, feature films and music videos tend to feature intensive artistic 'grading'. A clear example is the films of Michael Bay, such as Transformers and Bad Boys, which almost always feature heavy colour saturation and intensely warm colours. There are countless scenes that include orange 'sunset' tones, and these are the result of a decision to achieve that particular style, sometimes by using filters during shooting, but often using digital grading during post production. As I'm sure you can imagine, there is an opportunity to create some very heavily stylised footage with grading which, if used subtly, can dramatically enhance the finished product.

Colour Correcting

Colour correction can be carried out in any suitable video-editing software. Even the most basic packages feature simple colour‑correction plug-ins, and the most challenging aspect of the process is actually deciding if any correction needs to take place. In day to day life, our visual system is quite good at automatically correcting colour‑temperature shifts for us. For example, when moving into the shade on a sunny day, we don't tend to notice that the light has a very cool (blue) colour cast. The most important features of the Premiere Pro Fast Color Corrector tool are white balance, saturation and levels, which will help you to fix the majority of problematic clips.The most important features of the Premiere Pro Fast Color Corrector tool are white balance, saturation and levels, which will help you to fix the majority of problematic clips.

We also tend to perceive artificial light as quite natural, despite the heavy colour-shift. In reality, tungsten and fluorescent lights don't emit a pure white light. Unfortunately, our cameras, even on automatic white balance, don't always get it right, so we need to set the correct colour-balance option in the camera. Forgetting to do this will result in the footage having a noticeable colour-shift that will look unnatural. In order to compensate for any errors in post production, we need to look for colours where incorrect balance is clear.

We all know what white should look like, so that's the first 'colour' to look for. Do areas in your scene that should be white appear to be slightly blue or slightly yellow? If so, some colour correction will be needed. We can extend this method to other colours we know well, such as skin tones, red stop‑signs, green trees and the (hopefully) blue sky. If we can get those well‑known colours corrected, the rest tends to fall into place.

Within your chosen editing‑software, find the colour‑correction plug-ins. My NLE of choice is Adobe Premiere Pro, where the plug‑ins can be found under 'Color Correction' in the effects box, and there is a multitude of options to choose from. The user manual explains in detail how each plug‑in functions, but I'd recommend the 'Fast Color Corrector' for starters. Final Cut Express and Final Cut Pro feature a 'Color Corrector' which is very similar.

Most editing software should have colour‑correction tools available, but it's worth checking before you buy, as certain budget software, such as Sony Vegas Movie Studio HD, has very little to offer (go for the Platinum version instead, which is great value).

The first step is to apply the 'Color Corrector' to the clip you wish to process. Use the eyedropper tool by clicking on it and then selecting an area that should appear white in your video footage. This could be anything that you want to appear white, such as a white piece of clothing. If you click on something that is supposed to be another colour, you will get a very drastic shift, which won't look too good! If the eyedropper tool isn't working for you, or you find it difficult to find a white point, you can attempt to correct the colour manually using the circle in the middle of the wheel. By clicking and dragging the small circle you'll be able to shift the white balance of the image towards the colour shown on the outside of the wheel.

Once you've corrected the white balance, you can move on to contrast and levels adjustments. If you have deliberately shot footage with a 'flat', low-contrast setting, you will have to make some adjustments here. At this stage we can adjust black levels, mid-tones and the brightness of the whites. Several options are available in most editing software, including sliders for control of each range and similar eye‑droppers to the white-balance dropper. The black eye-dropper can be used to select an area of the image that should be black and, in theory, the input levels will change to achieve pure black. If that doesn't look right to you, you can revert, as with white balance, to the manual controls.

In Final Cut Pro, move the black slider to the left in order to darken the blacks and to the right to lighten the blacks, with the same method applied to both the mid‑tones and the whites. Each NLE will have slightly different controls, so do refer to the software's manual for more info. In Premiere Pro, the input levels can be adjusted to lighten or darken mid-tones, darken the blacks and lighten the whites. The output levels can be used to lighten the blacks and darken the whites. This is not quite as obvious as the FCP way of doing things, but you get used to it after a while.

Advanced editing software will include a three‑way colour corrector. This gives you separate control over the white balance of the shadows, mid-tones and highlights, and will also give you the option of secondary colour correction. Secondary colour correction describes correction focussed on a specific colour range. This is great for increasing the intensity of a slightly dull blue sky, or enhancing the saturation of some green foliage, for example. It's worth noting that you don't have to colour-correct or grade in your editing software. Final Cut Pro users have the grading application called Color at their disposal, while Premiere Pro users who also own After Effects (perhaps as part of a bundle) might prefer to use that programme for colour grading, as it includes the excellent Synthetic Aperture Color Finesse 3 plug-in.

One thing to bear in mind if you are trying to match up several cameras is to make sure to pick a 'master' camera and shot, and reference back to that when making adjustments to your other shots.

Scopes & Meters

The RGB Parade scope displays waveforms representing the levels of red, green and blue and is very useful for viewing the balance of tone in a particular clip.The RGB Parade scope displays waveforms representing the levels of red, green and blue and is very useful for viewing the balance of tone in a particular clip.Other than your eyes, there are some useful metering tools (also known as scopes) that can assist you with contrast adjustments. The histogram and RGB parade are the two I find to be the most handy. Anyone familiar with Adobe's Photoshop, Lightroom or Aperture software will probably be familiar with the histogram display and these types of level adjustments. The histogram displays the image luminance from black on the far left to white on the far right and everything in between. The RGB parade, on the other hand, splits the histogram information across the red, green and blue channel and aligns it vertically.

If the information in the histogram just touches each side, that is, in general, a good thing. If it doesn't, I'd recommend darkening the blacks and lightening the whites in order to achieve this. If you don't, the image may look dull or washed out. Don't push things too far unless you are trying to create a 'crushed' look (where both the black and white parts of the frame are exaggerated), otherwise you will lose detail in the shadow and highlight areas: shadows become solid black and light areas become pure white. While meters are useful, you shouldn't rely on them entirely. Use your eyes, and the adage that if it looks good, then it probably is!

Colour Grading Plug‑ins

There are a variety of third-party colour‑grading plug-ins offering more options than those found within your editing software. Unfortunately, these plug-ins aren't like Audio Units or VSTs, and tend to be made for specific host applications. It's quite often the case that budget NLEs aren't supported, so check before you buy! Some of my favourite plug‑ins come from the Magic Bullet Suite, which includes Looks and Mojo, and is distributed by Red Giant Software. Since there are so many different plug‑ins available, I'm going to use these to exemplify of the kind of grading processes carried out. These grading tools are intended for creating the kind of dramatic colour and tone shifts that enhance the style or impact of a scene, as opposed to just correcting subtle casts or tonal errors.

Magic Bullet Looks

Magic Bullet Looks is a powerful piece of grading software, allowing far more options than simple colour correction. Note the flow of effects from Subject to Post.Magic Bullet Looks is a powerful piece of grading software, allowing far more options than simple colour correction. Note the flow of effects from Subject to Post.Looks is an all‑in‑one colour-grading plug-in that can be applied to clips in the timeline. It works by opening its own interface, called LooksBuilder, which can also be used as a stand-alone programme for processing JPEG or TIFF images. A single license for the software allows you to use it in any of the supported hosts, which, surprisingly, include Final Cut Express 4.

While creating your desired look, you are able to view the current frame from your clip. To the left you will find the 'Looks' tab, a great place to start that features all available presets. Selecting a preset will place a variety of 'tools' in the area at the bottom of the screen. You can then modify any of these tools as required to create your desired looks. Alternatively, you can start from scratch, by selecting the 'tools' tab to the right of the screen, then dragging and dropping 'tools' onto the preview image. This will place the tool in the appropriate area at the bottom of the screen.

The 'tools' area is cleverly categorised into tabs based on the flow of footage through the camera and into post production. You can apply effects at stages named Subject, Matte, Lens, Camera and Post. Opening the 'Matte' tab, for example, reveals a variety of filters based on those that might be used in a real matte-box on the front of a film camera, such as sky and diffusion filters. Opening the Lens tab will allow you to add flares and the like, while opening the Post tab lets you pick from post-production and film-developing effects such as 'film grain', 'print bleach bypass' and the ubiquitous 'crush', which squeezes the black levels for a dramatic effect. The software also includes scopes that can be turned on or off using the 'Graphs' tab at the top right, and will show you when you're 'clipping' a colour.

By offering creative blurs, flares and stylistic colour effects, Looks distances itself somewhat from simple colour-correction tools, and is instead a comprehensive grading suite. Although Looks is designed for creating strong effects, it can also be used for subtle colour correction. The lift‑gamma‑gain tool, found in the Post section, is quite similar to the three‑way colour corrector found in other pro editing software, and wil allow you to make similarly subtle adjustments.

However, don't expect real‑time playback with a complex look applied, unless you have a very powerful computer with a high‑end graphics card. Preview rendering is required most of the time for smooth playback in the timeline, and the time taken to render the final film varies based on the complexity of the effects used.

On my i7-equipped MacBook Pro, I'm able to play back only very basic patches in real time, when Looks is applied to native footage from my Canon EOS 7D DSLR. This is actually still impressive, as playing the 7D's H264 codec is very CPU intensive. Looks retails for $399 and you can download a trial version from the Red Giant website.

Magic Bullet Mojo

The original image of Rachael Dadd performing live is very warm, and the skin tones look a bit orange. Using Mojo as the only plug-in, I've tweaked the sliders to create a more natural skin tone, helping to isolate the subject from the background.The original image of Rachael Dadd performing live is very warm, and the skin tones look a bit orange. Using Mojo as the only plug-in, I've tweaked the sliders to create a more natural skin tone, helping to isolate the subject from the background.Magic Bullet Mojo is a bit like one of those simple compressor plug-ins with very few controls that need to be moved around until something really cool happens! It can give you similar results to those you might achieve with Looks, but with less thought on your part. So if Looks sounds complicated, give Mojo a try. Mojo is designed to help you achieve the modern Hollywood blockbuster look (for example, a blue or green background tint while retaining natural skin tones). It works in a variety of applications, all of which are listed on the web site.

Mojo's controls are very simple, with limited options. Applying the effect to a clip gives you the default look, which can then be customised using the sliders. The Mojo slider controls the overall effect: moving it further to the right will push the background further towards a blue/green colour. The tint and balance controls significantly affect the colours, so it's best to experiment with these too. The 'Warm It' slider can either warm up or cool down the image, while 'Punch It' boosts the contrast (and can really help to bring out the subject), and 'Bleach It' affects saturation.

There are a few extra controls under the 'Skin' section that allow you to control how the plug-in deals with skin tones. 'Skin Color' will alter the skin tones within the shot, allowing you to correct unwanted colour casts. Moving left shifts the skin towards magenta and right towards green. 'Skin Squeeze' flattens the range of skin tones and 'Skin Solo' desaturates all colours in the scene except those that Mojo believes to be skin tones.

How well this slider works depends on how much of the image is taken up by skin tones, and it can be a bit hit and miss. The 'Show Skin' tick box will overlay a red grid on the areas that are the colour of skin. If you tick the box and don't see a red grid on areas of skin, move the 'Skin Color' slider around until the red grid appears over the areas of skin.

To be honest, when I use Mojo I tend to move the sliders around until the footage looks good! This plug-in is all about simplicity and fun rather than colour precision, and that's what I love about it, as well as what makes it great for beginners. It's a great plug-in and well worth the $99 price tag. Head to https://vimeo.com/9583345 to view an excellent overview of the plug-in.

Conclusion

Colour grading can be a complex and involved discipline similar to mixing and mastering, and entire books could be written on the subject, but you'll hopefully feel comfortable experimenting with colour correcting and grading your footage after reading this article. Do take the time to explore the colour-correction plug-ins in your NLE, as even a small amount of white balance and contrast work can make good footage into great footage. If your camera is capable, be sure to check out what kind of colour profiles you can use, and choose whether you'd like to achieve your 'look' in‑camera or at the post‑production stage. Also, if you can spare the cash I highly recommend investigating some of the third‑party grading software on the market, which will allow you to create more accomplished and stylish pieces with not too much effort.  

Picture Profiles

The Canon Picture Profile Editor for EOS DSLRs is a great way to create particular 'looks' within the camera itself.The Canon Picture Profile Editor for EOS DSLRs is a great way to create particular 'looks' within the camera itself.If you are a DSLR user, or user of a camcorder that supports a similar feature (such as the Sony EX1), it's well worth investigating the 'picture profiles' available to you on the camera. Most people tend to shoot stills using the 'standard' profile, which produces very good results. For video, however, it isn't always the best option.

You might have heard about the much derided aliasing and moiré caused by the 'line skipping' process in DSLR cameras. This happens when the camera scales the picture from its very high‑resolution sensor down to 1080p or 720p size. This unpleasant effect is made worse by the in‑camera sharpening, so it's best to use a picture profile with the sharpening set as low as it can go. On the Canon cameras, you can use 'Neutral' to achieve this.

For many shooting applications, this is good enough, but the customisation can be taken one step further by using the available custom colour profiles. These can either be something you've created yourself using the camera, or from the supplied software. The easiest option is to download pre‑made profiles from those who have taken the time to emulate various film stocks. On my camera (Canon EOS 7D) I've installed a Kodachrome profile, which I use quite often.

If you intend to colour-grade your footage heavily in post‑production, I'd recommend a 'flat' profile. The 'flat' image might not look great straight out of the camera and will require some grading in order to bring it to life, so it's great if you intend to grade your footage. There are many 'flat' profiles to be found on the internet for many cameras, but you can easily create your own. To do so in a Canon EOS, create a custom profile with sharpening at 0, contrast at ‑4, saturation at ‑2 and tone set to 0. By shooting with a flat setting like this you will be able to reduce aliasing (though not remove it, sadly!) and retain as much detail as possible in the shadows and highlights.

Quality Monitoring

A high-quality, accurate and calibrated monitor is very important for colour correcting and grading. It's a bit like the importance of good studio monitors in a properly treated room, when mixing audio. It is possible to spend large amounts of cash on a good display (such as the 30-inch Apple Cinema display for £1199$1599) but after investing in a good computer, software, camera, and so on, there often isn't much cash left for a top-of-the-range display!

There is nothing wrong with using a budget screen (there are some good full HD ones on the market for under £150$200, such as the LG W2261VP) but it's best to calibrate it correctly. To do this, you will need to purchase a calibration device such as the Pantone Huey or Spyder3. There are many to choose from and they range in price from about£60 $100 upwards.

In addition to working on a calibrated monitor, it's important to cross-reference your footage on other displays, just as you'd monitor a song you are mixing on many stereo systems. For most people, the best option is their TV. Your video might look very different on a TV display, due to internal processing and upscaling, so it's worth checking how things look before completing the project. To do this, I use a cheap HDMI adaptor that allows me to view footage from my laptop on the TV as if it were a second display. These adaptors can be found on the Internet for under £20$30.

Grading Software

As well as the Magic Bullet software listed here, there are other colour-correction and grading packages available. Magic Bullet have another trick up their sleeve, in the form of Colorista 2, which takes the colour‑wheel style correction you might find in an NLE several steps further and costs $299.

Synthetic Aperture's Color Finesse 2.1 straddles the boundary between correction and serious grading, allowing very accurate colour changes to be carried out in its separate interface. It costs $595 for the download version, running on OS X or Widows.

Users of FCP may be content with Apple's own Color software, which has been used in many productions and is very in‑depth, coming packaged with Final Cut Studio 3 for $999. An alternative for FCP users is The Grading Sweet 3, a package of plug‑ins designed to give easy access to filmic 'looks' and colour balances, without the need to go into the detail needed in Apple Colour. The Grading Sweet 3 costs $99, or $199 for the Pro Package, which adds a lot more filters.

Black Magic Design's DaVinci is the grading system of choice for high‑end productions, and was used to grade the highest grossing film of all time, Avatar. It can be purchased with a very large control surface for a eye‑popping $29,995, but luckily is also available as a software-only option for Mac Pro, costing $995.

Published September 2010