Facts About Printing
Colours on your Monitor Vs Printed
Different colours are made by adding primary colours together. On a monitor when you add primary colours together the secondary colours get lighter, but with a printer when the primary colours are added together the secondary colours get darker.
Printers Primaries are Cyan, Magenta and Yellow.
Monitors Primaries are Red, Green and Blue.
CMYK are the colours of the 4 colour printing process
During the printing process, colour pigment is laid down on the surface in patterns of tiny dots. Colour other than the primaries are created by varying the size and the position of dots of primary colours.
The challenge is how to transform colours from your monitor as the same colours as your final print product. This is translated through the digital image file.
Create a digital image
When your digital image has been converted from your monitor to a digital file, it has produced pixels. All the pixels together create a bitmap. A digital image file also contains information about the resolution at which it has been scanned and its Bit depth.
A black and white image can be expressed using only one Bit per pixel. Bit depth =1. Each Bit is either 1 or 0 (black or white). To express more colours on a monitor, more Bits are required. 4 Bits per pixel defines up to 16 colours. 8 Bits defines up to 256 colours, and so on up to 36 Bits, which can define billions of colours.
Are more Bits better for a digital image file?
No, not necessarily. The more Bits you use, the bigger the file size, which uses more memory and more resources for your chosen output device.
When an image is scanned, the data is recorded in a certain number of increments per inch. This is the image's scanning resolution and recorded as pixels per (linear) inch (ppi) of output. The higher the scanning resolution, the more pixels there are per inch. The more pixels per inch, the clearer the image.
Every device has different limits regarding its resolution and depth.
Remember - Viewing your image on a monitor is not an accurate representation of how your file will appear in print.
Any device that emits light, like a monitor or television, produces images by using an RGB or additive model of colour. Monitors produce colour by sending electrical signals to rows and rows of small red, green and blue phosphors behind the surface of the glass.
It is clear that different monitors and televisions emit the same colour differently. When you go into a TV showroom, many different kinds of TVs show the same colour differently. All monitors have slightly different colour gamuts.
You can change the monitor resolution to view the image differently.
A monitor set to 640x480 pixels will view your print document file very differently to it being set to 1024x768. Increasing the pixel size on your monitor greatly improves your opportunity to edit your image, pixel by pixel.
Another thing to remember is that if your monitor is not capable of showing you a 16 bit image, you will not see the richness of colour actually held in your image file.
The challenge for anyone placing a print order, is how to predict the colour output in the final print job.
Creating a 'soft proof' on your monitor
This is designed to see the placement of text and images and look at overall contrasts.
So, you can see that colour shifts in the translation from a device like a monitor to an output device, like a printer.
Before printing, the first level of proofing is on the monitor. This proof is called a 'soft proof'.
A soft proof is used to see the basic placement of text and images.
Creating a 'hard proof' - ready to print.
The hard proof is the printed document that is created by using the final output device. The final output device can be a laser printer or an interim proofing output device.
The advantage of running a print job on a digital production printer or press is that you can get a proof on the same device as the final print run.
Print ready file
A print utility in your input device, called a print driver, converts the proprietary code of the text, colour images, and colour information on a page to a file containing instructions the printer can understand. This file is called a print ready file.
To create a print ready file, simply upload your file and press 'print'. Then look for PDF, instead of a printer. Some programs allow you to Save as PDF.
How do printers create colour?
Different printing devices have gamuts. There are 2 main differences: devices that produce colour from pigment, dyes or toners use a subtractive model of colour to produce images. These devices lay down varying amounts of subtractive primaries (CMY) on the surface in the form of dots. Subtractive models for creating colour are also device dependant, because different manufacturers of printing devices and their associated dyes and inks use their own specification for defining colours. Printer gamuts are different to monitor gamuts. So blue on an inkjet printer might show up as more blue-green on your laser printer.
What is a raster image?
A raster image is made up of pixels (little squares) with a numerical value for their colour. All the squares are the same size and places in a grid pattern. Each one needs at least three numbers (for RGB) to calculate it's colour (4 for CMYK and 1 number for 8 bit colour like a gif) unless there is compression (like a gif, where large areas of the same colour are assigned a beginning and an end point and the colour value is assigned only once, or JPGs where an area of 8 or more pixels are assigned one of many algorithms built into the JPG codec).
Raster images cannot be scaled up in size because they will look pixelated when printed. And files that are high enough resolution for the printing process are usually very large. Use a raster image when the output of a raster image is exactly the size required for printing.
What is a vector image?
Vector graphics is the use of geometrical primitives such as points, lines, curves and shapes or polygons, which are all based on mathematical expressions, to represent images in computer graphics. "Vector", in this context, implies more than a straight line.
As a vector image, any colours can be assigned to the curves, including RGB, CMYK and spot colours. You could have a logo as pantone 567, pantone 490, 303 and more... In a raster you usually use a CMYK colour model or RGB. Sometimes you'll run across a duotone or tri-tone but these are not very common and definitely will not be usable in most office programs.
A combination of both of these tools is best practice. Both formats can come together. An understanding of the advantages and limitations of each technology and relationship between them is most likely to result in efficient use of technologies.
Scanners, monitors and printers all use different technology to produce colour. Scanners use CCDs or PMTs to record colour data. Monitors use phosphor triads, and printers use dots of toner, dye or ink to create colour.
Models to create colour
Monitors and scanners use an additive, RGB model for light, and printers use a subtractive, CMYK model for pigment.
The colour gamut defines the limits for each device. You might be limited what colours you can produce because of the colour gamut of your device.
The bit depth of an image determines the number of colours available to be assigned to each pixel.
The total number of colour possibilities that a pixel can have is determined by the Bit Depth.
The quality of an image is strongly influenced by the resolution of the printer. Printer resolution is determined by the maximum number of dots per inch (dpi) it is able to print. The more dots per inch, the higher the resolution and the higher the image quality. Laser printers used a fixed grid (Raster) upon which the dots of an image are printed or recorded. Many desktop printers print at 400,600,800,1200 dpi, and higher. Finer gradations in tones can be produced by higher resolution printers because their dots are smaller.
Printer bit depth
A black and white laser printer is a 1 bit printer. For any colour image, four halftone separations are created: one for each CMYK colour. For each colour, most printers produces halftones of C,M,Y,K.
Many laser printers can vary the value of each dot using advanced electronics. This is the printer's bit depth. Only when the dots for all four colours are laid down on the paper do we have the maximum colour possibilities for that printer. Therefore, an 8-bit colour printer produces much richer colour than a 1-bit printer.
Acid free paper - Paper made from pulp containing little or no acid so it resists deterioration from age. Also called alkaline paper, archival paper, neutral pH paper, permanent paper and thesis paper.
Artwork - All original copy, including type, photos, illustrations intended for printing. Also called 'art'.
Bit - A bit (a contraction of binary digit) is the basic capacitty of information in computing and telecommunications. A bit can have the value of either 1 or 0.
Bitmap - In computer graphics, a bitmap or pixmap is a type of memory organisation or image file format used to store digital images. It literally means a map of bits, a spatially mapped array of bits. Now, along with pixmap, it commonly refers to the similar concept of a spatially mapped array of pixels. Raster images in general may be referred to as bitmaps or pixmaps, whether synthetic or photographic, in files or memory devices.
Calibration - measuring and adjusting the performance of a device so that it performs as the manufacturer intended. Calibration controls the deterioration in performance of the input and output devices.
Characterisation - Characterisation is how we describe the colour gamuts for devices. The profile for a device must be created by the manufacturer for correctly calibrated machines. Characterising the colour gamuts of each device gives you optimal colour control.
CMYK - abbreviation for Cyan, Magenta, Yellow and Key (black), the four colour process.
Coated paper - paper with a coating of clay and other substances that improves reflectivity and ink holdout. Paper mills produce coated paper in four major categories - cast, gloss, dull and matte.
Colour Gamut - spectrum of colours that can be produced by a printing device
Colour name - hue
Commercial printer - Also called a 'job printer'. Prints specific product print jobs such as magazines, brochures and books.
Conversion - the translation of the colours from one device to another.
Desaturated colours - colours closer to grey.
Dot gain - Paper absorbs ink or toner in such a way that the dots spread out. This can alter both the colour and image quality of a document
DPI - dots per inch
Graphic design - Arrangement of type and visual elements along with specifications for paper, ink colours and printing processes that, when combined, convey a visual message.
Gsm - Paper gsm means grams per millimetre. It is measured by paper area density, not volume.
Hue - made lighter by adding white - tint
Hue - made darker by adding black - shade
Highly saturated - colours at their most colourful.
Job number - A number assigned to a specific printing project in a printing company for use in tracking and historical record keeping.
Multicolour printing - also called 'Polychrome printing'.
Neutral grey - grey with no hue or cast
Offset paper - paper that has not been coated with clay.
Offset printing - transfers ink from a plate to a blanket instead of directly from plate to paper.
PDF - Portable Document File
Pixels - A raster image is made up of pixels - little squares - with a numerical value for their colour. All the squares are the same size and places in a grid pattern.
Raster - A raster image is made up of pixels (little squares) with a numerical value for their colour. All the squares are the same size and places in a grid pattern.
Resolution - sharpness of an image on a film, on paper, computer screen, disc, tape or other medium.
RGB - abbreviation for Red, Green and Blue, the additive colour primary colours.
Soft dots - halftone dots with halos
Soft proof - digital image proof viewed on your monitor, generally used to see placement of text and images.
Solid - any area of the sheet receiving 100% ink coverage, compared to a screen tint.
Subtractive colour - colour produced by light reflected from a surface, as compared to an additive colour. Subtractive colour includes hues in colour photos and colour created by inks on paper.
Template - A template provides a standard lay-out. Outline of a printing project's basic dimension details.
Tint - adding white to a solid colour for results of lightening that specific colour.
Trim size - the size of the printed material in its final form.
Uncoated paper - paper that has not been coated with clay. Also called offset paper.
Value - the shade (darkness) or tint (lightness) of a colour. Also called brightness, lightness, shade or tone.
Vector - A vector image is the made of geometrical primitives such as points, lines, curves and shapes or polygons, which are all based on mathematical expressions, to represent images in computer graphics. "Vector", in this context, implies more than a straight line.
Virgin paper - paper made exclusively of pulp from trees or cotton, as compared to recycled paper.
Wrong reading - an image that is backwards when compared to the original. Also called 'flopped' and 'reverse reading'.
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