RAW workflow Basics
No matter how good your image manipulation, or retouching skills/post-processing skills are, there is a very real need to be able to extract the maximum quality and information from your camera’s RAW files.
As discussed in previous sessions, RAW files do not have any embedded colour profile data, any sharpening applied, etc. In fact, it’s just raw data, and nothing is decided until you export the file into Photoshop.
This affords many opportunities to correct many inherent defects or problems while the file is not locked into a fixed range of colour and tones, or colourspace.
The first issue is white balance:
While your cameras have white balance settings, these are only applied when shooting into a bitmapped file format (JPEG or TIFF). When shooting RAW, nothing is applied. This allows for much more flexible colour correction at the post shooting stage.
Adobe Camera RAW (ACR) is the software we will be using at the beginning of this course, as its part of Adobe Photoshop, and easily accessed by everyone in College. We will look at Lightroom and Capture One at a later stage.
In order to open RAW files in ACR, just open them in Photoshop, and ACR will load automatically if your camera’s RAW files are supported by your version. If you have many RAW files, it is best to multi-select the files using the “cmd” key (CTRL on PCs) and drag all files onto the Photoshop icon on your Mac’s dock.
ACR will open. (see below screenshot)
The files selected are displayed as thumbnails in the left column, and a large preview of the selected image is displayed centre.
When white balancing RAW files, part of the workflow you should be using happens at the time of capture by using a grey card. A grey card is a highly accurate grey card that is precisely neutral grey, and reflects 18% of the light falling upon it. They are used for exposure metering, but the other equally useful role they play is in white balancing.
As they are precisely grey, you can use the photographed grey card as a known reference point for white balance.
In the above screenshot, clicking the centre 18% grey swatch with the white balance tool….
…will colour balance the whole image to a neutral, correct value.
The real power of this tool at RAW level is when you have a collection of images all shot under the same lighting conditions. This is easy in the studio, as you’ll be in full control, and if you make no changes to your lighting, you know all the images are taken under the same condition. If this is the case, you can load all the images to be white balanced into ACR.
In the above example, there are three images taken under identical studio conditions that are not white balanced. You’ll notice the top image was a reference shot containing a grey card. If you select this image, then press “cmd” and select the rest… (see below screenshot)
You will notice that not only is the main previewed image now precisely white balanced, but the other images in the session have had the same values applied.
This method ensures precision across a range of images, and is particularly important in professional image making where colour is of extreme importance such as commercial photography where accurate representation of colours in products is needed. However, even if you decide to make creative choices to change colour within an image, you really need to start from a known accurate white balance.
This method only works when the lighting conditions are identical across the whole range of image from a session. If you try and do the same with a selection of images captured under differing lighting conditions, then you can not do this. (see below)
In the above scenario, one image was taken with flash, one under fluorescent lighting, and one under tungsten lighting. As the colour temperatures of all lights are different, despite having a grey card in one shot, the images cannot be balanced by applying the settings of one, to all. Every time lighting is changed; a new grey card image should be taken.
This is also true of location shooting. The colour temperature of daylight will change throughout the day, as the sun rises and sets, and clouds roll in and out. These changes are often imperceptible to you at the time, but the camera will record them. While on location, take a grey card reference shot regularly, especially if you are aware of changes such as cloud cover, or height of the sun.
No lens is perfect, and all lenses exhibit different characteristics. Some will distort straight lines slightly, some will vignette (darker corners) and some will exhibit what is known as chromatic aberration (CA).
CA is when light at one end of the spectrum (red for example) cannot be focused at the same point as the other end (blue), and this results in a coloured fringe around objects, usually blue or cyan on one side, and red or magenta on the other. This is most noticeable in high contrast subjects such as tree branches against a bright sky.
ACR (and Lightroom and Capture One) have tools to remove this if you are using a sufficiently up to date version.
In ACR, this is in the lens Correction tool palette.
If you select the color Tab, there will be a box to tick to remove CAs.
Tick this box and the CA will simply be corrected. (Some types of CA will never be removed, but this will mainly be colour fringing in out of focus highlights or background detail (bokeh).
ACR (and Lightroom, Capture One) allow you to apply what are known as Lens Profiles. These are preset corrections to perspective (straight lines being bent) and evenness of tones throughout the image (vignetting) that are pre-written for each lens type. As your images are embedded with metadata (EXIF) that describes the camera settings etc. the software knows what lens you were using, and when the “Enable Lens Profile Corrections” box is ticked, your lens profile should be applied. (see below screen shot).
There are also manual controls under the manual tab to experiment with if you want to ADD distortions intentionally, or make manual corrections to images taken with no metadata (or with lenses without a profile).
Images taken using higher ISO settings will obviously contain noise (grain), and again, this is best dealt with at RAW level (although it is possible in Photoshop, it’s best corrected at this stage while the RAW image is being corrected for other issues).
The thing to remember here, is that this is noise REDUCTION, not REMOVAL. You will never completely remove noise from an image unless it’s very subtle to begin with. Attempting to do so can result in other problems being generated such as loss of detail.
Noise reduction in ACR is located in the “Detail” palette.
There are four main controls to Noise Reduction in ACR (and Lightroom).
Adjusts edge definition. Increase the Amount value to increase sharpening. A value of zero (0) turns off sharpening. In general, set Amount to a lower value for cleaner images. The adjustment is a variation of Unsharp Mask, which locates pixels that differ from surrounding pixels based on the threshold you specify and increases the pixels’ contrast by the amount you specify. When opening a camera raw image file, the Camera Raw plug-in calculates the threshold to use based on camera model, ISO, and exposure compensation. Values higher than 50 usually make the image look over-sharpened.
Adjusts the size of the details that sharpening is applied to. Photos with fine details generally need a lower setting. Photos with larger details can use a larger radius. Using too large a radius generally results in unnatural-looking results.
Adjusts how much high-frequency information is sharpened in the image and how much the sharpening process emphasizes edges. Lower settings primarily sharpen edges to remove blurring. Higher values are useful for making the textures in the image more pronounced. Use mainly low settings to retain a realistic looking image. Higher values make images look “gritty” and over sharpened.
Controls an edge mask. With a setting of zero (0), everything in the image receives the same amount of sharpening. With a setting of 100, sharpening is mostly restricted to those areas near the strongest edges. Press Alt (Windows) or Option (Mac OS) while dragging this slider to see the areas to be sharpened (white) versus the areas masked out (black).