Guide for Creating Printing Data
Example of raster images include photo taken with digital camera, image created with Photoshop, etc.
Raster graphics render images as collection of countless pixels, hence, image quality is determined by the resolution.
There are many file formats which are categorized under raster image, among those are JPG, PNG, PSD, PDF and etc., however, it is difficult to determine whether there is raster image created with file format such as CDR, PDF, EPS and AI.
It’s highly stretchable with no maximum or minimum limit for sizing, while maintaining the image quality.
The outline processing function allow user to modify the font of the image.
Despite having numerous advantages over raster image, one limitation is that problem may rise when converting vector image into printing data and the image has to be rasterized with resolution that compatible to printing process.
There are various formats such as PDF, Al, CDR, EPS, etc. for vector images, all these files can be saved as raster images, however one should always check all components before saving for printing used to avoid broken files.
RGB and CMYK
Since these are light, the higher the density, the brighter it is.
A monitor or a television is perfect example of media that display images with light.
The color densities for printing is represented by four different inks CMYK, which are Cyan, Magenta, Yellow and Black (K=Black).
In contrast to RGB where color becomes brighter when all three colors are mixed, the mixture of CMYK generates darker color.
Therefore, a mixture of 100% concentration CMYK will generate a vivid black color.
Monitor and Printing Color
With rapid technology development, when CMYK color mode is selected on design software (Photoshop, Illustrator, Corel, etc.), user is able to predict the color output of their designs.
Despite not 100% accurate, it can serve as a preview for the final output.
Colors will always differ when printed on paper especially high saturated color such as pink and fluorescent which are printed separately form CMYK, the color contrast tend to be more visible.
Color differ slightly when seen on different monitors in the same company.
Similarly, for printing machines, it is not possible to generate the exact same output even printing is done with same machine model within a company.
Colors varies depending on different textures, ink absorption, drying speed and other features of the paper.
Even with same paper, the humidity and temperature of the day can affect colors presentation.
Monitors presents colors with lights, while printing presents colors using a collection of 100% density points (dots), hence, the lower the density, the weaker the color is.
Spot Color and Process Color
When this happen, the colors value available in PANTONE and in CMYK color conversion table displaying each spot color will changed into CMYK values for print. If colors are created randomly without a color conversion table, the created value seen on the screen will be set to represent spot color and printing process will take place. For example, if user created spot color randomly without using color conversion table, if the color value on the screen is (M100, Y100), hence, for machine that recognizes only CMYK color system, only red color will be printed.
Therefore, when printing is needed, all spot colors used for the designs should be converted into CMYK colors to prevent printing error.
Below are some of the problems that may occur when prinitng with low resolution.
Aliasing: An image composed by dots will be clearly visible (such as picture, (JPG), small rectangular groups that formed the picture will be visible when enlarged.
Small jagged staricase like pattern are formed due to low resolution and it is called aliasing.
Since common monitors has no problem displaying images even with only 72 DPI resolution, small jagged staircase can be seen on the screen and will shows on the final output unless the resolution is set to be printable which is 300 DPI or higher.
Blur and dull output: To prevent aliasing problem, an image with 72 DPI will be changed to 300 DPI for printing purpose, and this adjustment solved the problem of visible aliasing on final output, however, the picture might appear blur and not sharp.
For example, when zoom into a picture of earth with high resolution, the people in that picture will be visible, same principle can be applied in zooming into picture with low resolution, the square is enlarged, hence, it will not appear on the output and only a blur and unclear big square will be seen.