Evaluation Using a Video System

The first publications on the evaluation of thin-layer chromatograms by image processing appeared as early as the mid-1980s [118], These methods, also known as digital evaluation , were presented to the scientific world in the lectures of Prosek, who developed his own software for the purpose in 1991 [119], although only the enormous developments in the hardware (video cameras, computers, printers etc.) have made video evaluation of thin-layer chromatograms economically justifiable. Prosek presented his paper on the validation of quantitative TLC by video camera in 1997 [120]. 

Digital images consist of information about the intensity and color of light at thousands of separate points on the image. These data consist of numbers, encoded as a series of zeros and ones, that are transferred in the form of electrical impulses to or from the microprocessor of a computer and are then translated back into an image on the computer screen. 

No digital image is as good as the human eye s view of an actual object. The smaller the number of stored points of the image (known in computer terminology as pixels) the poorer is its quality. 

The second criterion of quahty is the depth of color of a digital photograph. This depends on the number of colors encoded for 256 colors, eight digital characters (bits) per pixel are necessary. A color intensity of 16 bits enables 65 536 colors to be represented, which is known as high color . An almost photographically reahstic representation ( true color ) is only possible with 16.7 miUion colors, and this requires 24 bits per pixel [121]. 

Modular systems of the latest type for the production of images and documentation of thin-layer chromatograms consist of four components. 

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