SHIL standards
- Former user (Deleted)
- jr_barnes
Industry grade standards are used with every digital camera in the Imaging Specialist's lab. Each standard is designed to accurately calibrate your images to ensure you are not making subjective decisions when it comes to replicating true tones and colors. There are 4 common types of standards used for the SHIL that correct for: white balance, glare, color, and topography.
White balance
> QP Cards 101
A gray card is useful for setting or correcting the balance of neutral colors, as well as for exposure. On the SHIL, we use the QP card 101 for calibration and quality monitoring throughout an expedition.
Figure 1: QP card 101 v4. Note, you should see a tonal difference between the light gray patch and the white backing. If you cannot, you have over exposed your scan.
Key Features
- Three spectrally neutral patches, where the spectral response of the three colors is almost perfectly straight
- Neutral grey patch with 18% light reflectance
- White and black patch (for contrast adjustment)
- Millimetre reference scale on the side
- Adhesive on reverse can be attached to most surfaces
- Designed for longevity and is fade resistant for precision over a longer period.
- Dimensions: 14 x 4cm
Caution: The newer version (v4) have near black and near white instead of pure black and pure white (middle gray is the same), compared to the older versions. Know what version you are using! They have the L*ab color values for each patch printed on the back side, which can simply be converted to RBG.
QP 101 Version 4
| Dark gray | Mid gray | Light gray | |
|---|---|---|---|
| L*ab | 34, 0, 0 | 47, 0, 0 | 93, 0, 0 |
| RGB | 80, 80, 80 | 111, 111, 111 | 235, 235, 235 |
You can find these in the Close-up box, SHIL draw in the Core Lab or in the Imaging Specialist's Office.
Glare
> Red reflectance bar
The highly reflective red bar at the top of the track is there to monitor glare. Please keep this bar clean.
The magnitude of the glare can change depending on the angle and intensity of the light. The Law of Reflection explains that light that hits a reflective surface at an angle (like the front of a person’s eyeglasses) will be reflected back at the same angle. In other words, the angle of incidence equals the angle of reflection. Identifying the source of the glare (the lighting), the angle of incidence, and the reflective surface are critical factors to reducing or eliminating the glare in your SHIL scans.
Figure 2: Example of two scans, one with good reflectance (left) and one with poor reflectance (right).
Color Management
There is a difference between good color and accurate color in your photographs. Every combination of lens, camera and sensor reproduces colors in its own unique way from a wide range of colors. And this combination can then change as the lighting conditions change. Not to mention that cameras don’t record colour data the way our eyes perceive it. This is why we use color checkers, to act as an accurate color reference.
A gray card will help you get accurately controlled white balance, but doesn't necessarily account for every single color in your image. A gray card accounts for the overall temperature and tint, not every color individually.
X-rite ColorChecker Mini
Color calibration target consists of a cardboard-framed arrangement of 24 squares of painted samples. The chart’s color patches have spectral reflectances intended to mimic those of natural objects such as human skin, foliage, and flowers, to have consistent color appearance under a variety of lighting conditions.
Caution: The pigments for ColorCheckerPassport were modified in November 2014, so the current 2019 available cards do not have exactly the same carnation as the 2014 cards - Make Note of the version you are using.
The 2014 versus 2019 Xrite color checker RGB values are listed below and a link to the excel spreadsheet is here. Note that those new 2019 RGB values are calculated from the L*a*b* values using the calculator found at www.davengrace.com/dave/cspace. A spreadsheet calculating RGB values are various illuminants is here. We found the illuminant A was actually closer to our lights, other illuminant should be tested.
