Last Updated: 13/04/2016
basICColor Grey Card
grey card free of metameric effects, the proper way to grey-balance a capture
Color–solutions have produced a rather special and very useful digital camera white balance target, basICColor Grey card has excellent grey balancing capabilities. Being able to achieve a properly accurate neutral balance is an extremely useful aid for a digital photographer and it's of utmost importance what type of card or material is used for this purpose, many products are very poor at the job because of metamerism. The basICColor Grey card utilises a superior type of material specifically made for the white balancing (i.e. neutral or grey balancing) of digital cameras. (also see basICCaliCube)
Because of its very good spectral remission properties, basICColor Grey card is virtually free of metameric failure. The color shift under different lighting situations is below the threshold of visual perception. In brief, the basICColor Grey card looks the same in all viewing conditions: Grey without a cast. Most Grey cards do not have this property.
it's worth understanding the practical science behind this
Digital photography offers the user a wide range of new possibilities. Colour fidelity in particular can be improved tremendously. Instead of two conversions (Original object via Photography to Film, then, Film via Scan to File) only one "conversion" is required (Original object via Photography to File). Colour conversion from original to film is obsolete. In a film based workflow, although the original to film step is not easily controlled, the scanning process can deliver very exact colour reproduction - when good colour management is applied.
In digital photography, the capture and the scanning process are effectively merged and this eliminates colour problems intrinsic to film that sometimes cannot be corrected.
So, digital capture has a big advantage, but in order to achieve exact colour reproduction, the digital camera needs to be calibrated and profiled – just like the scanner – in a conventional two step process.
Variations in lighting conditions present a special challenge in digital photography. Whilst all ICC – compatible programs (camera software, Photoshop, InDesign, RIPs, etc. . .) are based on the ISO standard lighting of D50, digital photography is dependent on the actual lighting in the current scene.
When viewing objects under different illuminants, metameric failure will occur regularly, this means that although the colour of two objects might look the same under one light, they may cease to match under a different light. In everyday life you see this effect when shopping for clothing – clothes which match under shop light may not match under sunlight. Shoes and handbag? Grey jacket and trousers? We've all seen this.
Of course if objects don't match each other under your actual shooting light, then no amount of colour management or use of a white balance or grey balance is going to fix that. But, using a high quality non-metameric grey card simply means that the grey card itself always "looks" grey and, thus, balances the capture correctly which is an excellent first step to high quality results.
The chosen neutral balance target bears a special relevance in respect to metamerism. If the photographer uses a metameric Grey card for this purpose (and many commercially available Grey cards are metameric) all images where that card has been used under a non – D50 lighting situation will produce a colour cast, even though the camera had been calibrated to Grey. Because that grey has "failed" to remain neutral, a colour cast will appear, depending upon the type of metameric failure. This effect is known for most Grey cards, even from well known manufacturers in the photographic and colour management arena. That’s why basICColor developed this very special Grey card.
For all the reasons above the basICColor Grey Card is perfectly suited as a reference for grey and for lightness comparisons for all systems used in digital photography, especially when used in combination with the Color Solutions desktop background for your display (shown right) - this file is included on the CD included with basICColor Grey card.
use the basICColor Grey card for:
- White balance of digital cameras for profiling and shooting
- Exposure meter (digitally via colour picker with camera ICC profile active)
- Lightness setting of viewing booth and monitor (visually and instrumented)
- Light meter for adaptation of colour temperature between monitor and viewing booth
- visual check of monitor calibration
The basICColor grey card was developed in line with the production principles of the European Colour Initiative ECI information here. At the ECI site you can also download the working space eciRGBv2 in which uses the superior L* (L-Star) tonal characterization (rather than a gamma curve) as used in the theoretically ideal CIELAB colour space. info here.
L* is actually the ideal tonal response curve for calibration of monitors used for imaging work. L* allows for a harmonic distribution of grey-scales, in accordance with the human perception, and detail in mid-tones and highlights. basICColor were the originators of this idea - so, of course, basICColor Display software includes the L* calibration option .
At workstations set up this way for use with imaging programs, the operator will ideally choose a mid-tone grey (RGB=153) as desktop background. This grey equals L*=60 under an L* calibration. The achieved lightness level is best suited for checking the grey representation of your monitor, since colour casts are more irritating, more noticeable, in light and mid-tone greys than in the dark tones favoured by some operators.