Offset printer & the quality of printing

    Offset printers enable the greatest option when big quantities are required, as it gives accurate colour reproduction and crisp, professional-looking printing. Offset printer is best known for providing accurate colour reproduction, and crisp, clean professional-looking printing.

    Most people think of “offset lithography printing” when they consider the commercial printing of books, magazines, flyers, brochures, business cards, and catalogues, etc.

    With an offset printer, the image to be printed is generated or etched onto a flat surface (the plate) such as a sheet of aluminium, plastic, or zinc during the offset lithography printing process. The picture is then transferred to a rubber roller before being transmitted to the substrate. The procedure is relatively straightforward and is founded on the fundamental idea that oil and water do not mix. There are several phases involved in transforming an image or text into a printed page.

    In lithography, the plates are coated with a photosensitive (light-sensitive) emulsion and have a roughened surface. This emulsion is a suspension of two substances that are incompatible with one another. Plates can be created in one of two ways: exposure from a light source with film on top of the plate, or by utilising a system that exposes the plate with lasers straight from a computer (CTP).

    What is the best quality image for Offset printer?

    The basic rule of thumb for offset printing and digital printing is to have halftone images with a resolution of around 2 times the line screen (also known as the halftoning factor).

    Image resolution equals image line screen multiplied by two

    Printing at 150 lpi requires an image resolution of 300 ppi (150 lpi x 2 = 300 ppi). For printing at 200 lpi, you will need an image with 400 ppi (200 lpi multiplied by two is 400 ppi). When it is unavoidable to prevent embedding text within non-vector visuals, the image resolution should be adjusted to 600 ppi or higher. Line art resolution should be 1200 ppi.

    If you intend to expand your photographs, you should be aware that they will lose quality. Size is inversely proportional to image resolution. A 200 percent enlargement of a 300 ppi image results in 150 ppi. Consequently, the same formula can be extended to:

    (image line screen multiplied by two) x magnification

    Therefore, if you are printing at 150 lpi and increasing the image by 200 percent, you will require a 600 ppi graphic ([150 lpi x 2] × 2 = 600 ppi). If you magnify an image by 150 percent, you will need a graphic with a resolution of 450 pixels per inch ([150 lpi x 2] x 1.5 = 450 ppi).

    As a general rule, images used for common printing services should be at least 300 ppi at 100 percent of the ultimate size. Higher screen frequencies in offset printing demand higher quality bitmapped pictures.

    Offset printer uses for offset printing, also known as lithographic or ‘litho’ print, provides more options for larger or more sophisticated printing projects. It also permits the use of a larger variety of paper stocks and finishing processes. Offset printing is ideal for printing huge quantities because it is the most cost-effective printing method.

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