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Using A Densitometer To Mensurate Plates

Despite what you lot may receive got heard from vendors Using a densitometer to stair out platesDespite what you lot may receive got heard from vendors - yes, you lot tin role a densitometer to read starting fourth dimension plates. This tin last peculiarly helpful for the smaller printshops who may non receive got the resources to buy dedicated plate readers.

Densitometer basics

Color reflection densitometers are designed to accurately stair out Black, Cyan, Magenta, as well as Yellow colorants on substrates similar paper. However lithographic plates commonly don't receive got C, M, Y, K images on a white substrate, instead the plate fabric is commonly brushed aluminum amongst a grayness color. The color of the icon itself volition vary according to the plate type as well as vendor.

You withdraw to last aware of these reflectance as well as color properties since they upshot how you lot role your densitometer when evaluating your plates.

Contrast

Because of plate color properties, the contrast betwixt icon as well as and non-image areas of the plate is typically less than one-half that of ink on paper, every bit a resultant it may non last possible to calculate dot expanse for some densitometer/plate combinations.

Aperture size

The densitometer aperture (measuring window) should last the largest possible for your build of musical instrument - every bit long every bit it's non larger than the icon expanse you lot are measuring. This helps average out the reading as well as minimizes the upshot of random plate patterns.

Densitometer Status

The musical instrument should last laid to "Status T" unpolarized inwards business office because this setting has a wider reply to the diverse plate coating colors.

Consistency is to a greater extent than of import than absolute accuracy

Conventional as well as digitally imaged plates typically role the same aluminum base of operations material. However the dissimilar types of mechanical or chemic graining that prepares them for lithography results inwards a dissimilar surface texture which inwards plough scatters low-cal differently. In gild to arrive at consistent dot values. To assist arrive at consistent dot value measurements, you lot should endeavour to hold a consistent alignment of the densitometer to the plate. Perhaps using the base of operations of the densitometer aligned to the border of the plate. Also, zilch the densitometer as well as read the 100% expanse on the same location each fourth dimension as well as receive got readings from the centre of each target patch.

If you lot know that a acre on the plate represents a 50% musical note (i.e. it is a checkerboard) but your densitometer reports the acre being, for example, a 54% musical note acre the plate prints correctly on press as well as then 54% becomes the target for that acre on the plate. The persuasion is that you lot are controlling your plate imaging procedure past times monitoring as well as minimizing variation. Your priority is to hold consistency inwards the measured dot areas.

Alternatively you lot could modify the dot gain calculation "N" factor. Densitometers role 1 of ii formulas for measuring dot area; the Murray-Davies or the Yule-Nielson equation. They are the same equation withal the Yule-Nielson equation utilizes an "n"-factor to "factor" out the optical dot gain (the Murray-Davies equation is equivalent to the Yule-Nielson amongst n laid to 1.00). The n-factor is experimentally determined past times adjusting it until the densitometer reads the ‘desired value’ at a known dot percentage. Typically a 50% musical note is used because it is slowly to spot. You'd impress a expose of musical note values roughly 50% (e.g.45% as well as 55%) as well as then role a loupe to uncovering the musical note acre that ‘looks like' a 50% musical note - a checkerboard. Next accommodate the n-factor on the densitometer until that acre reads 50%. The n-factor is typically applied when a densitometer is used to stair out printing plates since printing plates are assumed non to receive got whatsoever optical dot gain.
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