1. Densitometer and Density : A photo-electric device that measures the degree of darkness of the photographic material or degree of light transmitted or reflected back from the surface of an opaque object to calculate and set density values of the negatives and positives processed for printing. The reading on the negative/ positive will indicate how dark is the processed area. The films are basically coated with silver halide and when exposed the exposed areas will become black. The density reading consists of minimum 0.05 (D min) to maximum of 4.00 (D max) which help to adjust exposures for producing correct set of negatives/positives for further processing.
The density measurements between the two extremes which are dark to lightest area indicate whether correct exposure have been given, as well as processed with correct time factor in the developing solution. Usually a standard density wedge available with the photo material suppliers - band of paper or film showing graduated tones ranging from white to black- is used as the test image for these measurements.
The density reading also help in adjusting the ink levels i.e ink film thickness called solid ink density during the printing process. This values are compared with the standard color strip printed on the edge of the sheets or with the standard color strip kept offline. The color wedge is an image that is printed across the press sheet, usually on the trailing edge, that contains targets to provide measurement areas for the solid ink densities, dot measurements etc. The colour strips are provided as standard film wedge and exposed onto the plates along with the image .
There used to be some confusion to the printers. Are the terms opacity and density the same? Yes technically both are same in respect of negatives and positives whose measurement is taken by transmission densitometer, but in respect of prints, they are not to be considered same term. The readings of Density and Opacity are measured and expressed in different values.
Densitometer is a useful tool if you want to maintain consistency and quality in the work. Universally two types of density meters are available :
Transmission densitometers that measure transparent materials such as negatives, positives and transparencies. The densitometer measures the amount of light transmitted through the transparent material. It determines the opacity for different areas of transparency or of the processed film negative or positive.
Reflection densitometers measure the surface which is the print area or the image area of the original being processed. The reflection readings are taken to calculate total dot gain, error in the colour shade, grayness of the area, and other characteristics in the printed work.
However some densitometers are also equipped to measure both transmission reflective substances.
How densitometer will be useful? It is common knowledge that everyone sees the colors in their own way and they cannot be standardized judgment or calibrated like the densitometer because each ones eyes may have some defects or differences. Ones’ eye can not see the color of the object in the same hue as seen by others. For example a pure green printed patch may look dull green to some one, some other may see them as pure green, while others may say it as slightly bluish green and so on. This is because each one eyes are influenced by the light source. The eyes can not therefore be a barometer to measure the strength uniformly and only a densitometer can give the correct ruling.
2. Die: A metal plate made of steel or some hard metal as male die or male and female combination to produce embossed image or only a male die to produce debossed image design on paper or other substances. This process is called Embossing or Debossing.
Also the special shaped cutting tool prepared to get the paper or other substances cut to some specific shape and size is called dies and the process is called Die cutting.
The die making is an special art carried out by engraving process and the artist engraves the images manually. Now the dies are also prepared on electronic machines. The paper or substance which require to have the embossing or debossing will be inserted between the male and female dies and then given a heavy pressure to create the image on the material.
As far the special shaped dies they are carefully prepared with sharp edges to cut the material to a particular shape and therefore will not have a female die as its combination. The paper or substance to be cut to specific shapes are kept below the dies on a platen frame and dies pressed against the substance to trim them to shape. Almost any shape can be created and applied to prepare Labels, envelopes, folders, cartons.
3. Debossing or embossing : The opposite of embossing is called debossing. Instead of a raised image, letters or images are depressed into a sheet with a die in the debossing process. Embossing and debossing are two processes of getting relief or depressed images on the paper or other substances using heat and force. The procedure involves the use of two etched metal dies in both the cases . A raised male die and recessed female die. Both will fit into each other . A die maker engraves the desired design into the metal plates which is called the master die. The die with relief images will force the paper or the substance into the recessed die to create the embossed or debossed impression. Embossing creates a raised impression while debossing creates an indented impression.
A die maker engraves the desired design into the metal plates which is called the master die. Embossing is generally the process most often employed to attract attention or convey high quality textural contrast in relation to the surrounding area. Three dimensional effect can be produced by die printing process. The more elaborate the design and etching, the more costly it is to make the die.
4. Direct Imaging: This process, also known as Copy to Plate is a new technology that directly transfers the digital image to press plates using laser beams. The advantage is improved resolutions of the images and print quality as well. For details read under Copy to Plate. This is the age of digital or direct imaging . Since the laser records the images onto the plate exactly as per the digital files stored on a computer, the print quality will be excellent. Moreover the manual steps of conventional prepress work such as producing films, preparing the films for plate making, making plates, and mounting and registering plates on the press etc are all eliminated. There are equipments available which can be attached with the offset presses to store the spool of special plates meant for direct imaging. As soon as the new plate is made ready by direct imaging process, such plates are automatically fed onto the plate cylinder from the spool. This reduces the make ready time drastically. However such machinery and equipments have not replaced the existing printing processes and are slowly gaining entry in to the printing presses in Europe and American countries.
5. Dot: Also known as a pixel, the smallest element or a partial image of a halftone.
6. Deckle Edge : Term used in paper manufacturing technology is meant to to indicate the uncut, uneven paper edge that comes out of the paper making machine which is finally trimmed to make them have perfect cut edge while slitting.
7. Doubling: This is a Printing defect that occurs due to loose blanket or paper slipping during impression in the printing machine. The cylinder packing, grippers not holding the sheets firmly, worn out plate or blanket cylinder gears, static charge (Static electricity) on paper, use of different blankets on the same machine etc , also causes this defect. The image will appear blurred or shadowed.
8. Duo tone : Printed from two halftones, with two colors, one shot for highlights and the other shot for middle tones and shadows. Two plates with a difference of 30° angle between them will normally be prepared and printed to get this effect. For example if one plate is prepared with 15 degree angle screen, the other will be prepared with 45 degree angle screen in position. Thus printing an halftone image superimposing of one dark colour over another light color will produce this effect. This process is not to be confused with colour separation. The expert printing presses exclusively printing duo tone keeps separate set of inks to give depth to the print quality. The duo tone concept has enlarged to tri tone printing, meaning printing the same image in three colors with different screen angles, then quad tone again printing the same image with four tonal shades.
............Additions to alphabet D to be continued under D/2