RAW' Topical Cream

Today we are going to get into the nuts and bolts of ACR (if you don’t know by now that is Adobe Camera Raw). First we look at the histogram and what it is telling us. Secondly will be the most used panel in ACR and that is the BASIC panel. I titled this Topical Cream as it is the first contact you have with the digital negative. You use the OTC cream before you go to the doctor don't you?

HISTOGRAM - This is a graphic illustration of the luminance (brightness) and tonality of the data captured by the cameras sensor. Not only does it provide an idea of the overall quality of light shown by the white area, the RGB channels are also represented. The histogram on the back of your camera is based on the JPEG image that is being shown on the camera display. Often times people will notice the RAW image does not look like the one on the camera display. This is because the displayed image is a processed JPEG and the RAW image you import into ACR is not. At least not until you process it. The beauty here is that you have total control over what the outcome will look like given the quality of the initial image.

The horizontal scale of the histogram represent the tonality and the vertical magnitude of each tone shows the pixels as a ratio of total pixels available. This is where bit depth comes into play. Ansel Adams and Fred Archer came up with the Zone System in 1941 quantified the values of light across eleven tones of light from black to light. With digital this equates to values of zero (black) and 255 (white). The RGB values use the same scale. In digital when tonality is in the 0 or 10 zone they are considered to have no usable data and are blown out or clipped. The histogram is manipulated by adjusting the sliders in the BASIC ACR panel discussed below.

BASIC - If there were to be only one panel available to correct a digital RAW file, this would be it. Most images if shot with any skill will only require a slight adjustment in the BASIC panel and they should be good to go. The BASIC panel is broken down into three sections, White Balance, Exposure, and Clarity. I futher devide the Exposure section down to Brightness.

White Balance - If the white balance is not correct the image will not represent what you were looking at when the image was captured. It can also be used in an artistic fashion to enhance the image as the artist you are.

The temperature value is calibrated in Kelvin while the tint scale is relative. As seen in the diagram below, the White Balance drop down window will show the white balance options that are available in the particular camera you used. In this case it was a Canon G9.

Expose - The exposure section of the BASIC panel includes actual Exposure, Recovery, Fill Light, and Blacks. Additionally it contains Brightness and Contrast but we will separate that for now.

Exposure - As this slider is positioned the values represent stops of light as a reference. This effect the entire image and changes can be seen in on the histogram.

Recovery - The recovery slider is used to pull data away from the clipped edge of the highlights and those in zone 10 (255). This is where RAW shines as there is always more data in the file than in a JPEG. When you slide this slider to the right you will notice the right side of the histogram move towards the center.

Fill Light - This is pretty much opposite from Recovery. When the histogram is shoved over to the left side and exposure has been adjusted, further shadow boosting can be made by use of the fill light slider. Here when the slider is moved to the right the left side of the histogram will move towards the center. Pushing this slider too far can generate noise as it may be generating data from nowhere as it interpolates and inserts information.

Blacks - This slider should be used with great care. It essentially resets were black is defined. I rarely use this slider unless the image has enough high end exposure to support the push.

The Missing 2 - Brightness and Contrast are actually part of the exposure section of the BASIC panel but there use is not as relevant as the others.

Brightness - This slider simply boosts the luminance of the entire image. Unlike exposure that adjusts data, brightness adds data across the board. I rarely use this slider.

Contrast - This does exactly what it says it does. Depending on the version of ACR will determine the effectiveness of this slider. Version 5.2 and Lightroom 2.2 provides a very good quality with this slider. If I am working in Elements I will generally use Levels and then Brightness/Contrast in the Adjust Lighting option under Enhance. Mostly as an adjustment layer though as this is lossless.

Clarity - Adds depth to an image by increasing local contrast. It is a form of sharpening and is best adjusted at 100% zoom. To maximize the effect, increase the setting until halos are seen near edge details and then reduce the setting slightly. There are many levels of sharpening; In camera, Processed, and Output. In camera is what is done to a JPEG, processed is what is done in Photoshop/Elements, and output is what is done prior to printing for the relevant print resolution.

Saturation - I have skipped Vibrance for the moment. Saturation will boost the color luminance value across the board on a linear basis. Blues are bluer, greens are greener… You get the idea.

Vibrance - No this one is where the magic happens in ACR. This act similar to the Saturation slider only it leave in a non-linear approach. This means that when you apply a Vibrance adjustment, the less saturated colors will get more of a saturation boost than those colors that are already saturated. The real benefit results in that it generally leaves facial toning alone. Cool stuff.

Ok… That was a good bit if info. Tomorrow we will get into the Curves, Hue, Saturation, and Luminance panels.

See You then… Doug