Thursday, December 16, 2010

Illustration Resolution Information

What resolution should I use for what purpose?
72 dpi is the default resolution of images used on the World Wide Web, but you will need to reduce the number of pixels using a Photo Editing program, for instance the 4 Megapixel image we used as an example earlier was 80 centimeters wide! At 72 dpi an image of 800 x 600 (28cm wide) will just about fill your entire computer screen but is only half a Megapixel in size. Most Images on the web are much smaller than this 200 pixels wide is common for instance, but it entirely depends on the design of the Web page.
150 dpi is a good resolution for images used in documents for printing to your local printer. For instance internal documents used in either business or schools where the documents are printed on a Laser or Inkjet printer and need to print in quantity and at a good speed.
300 dpi is the default resolution used for Offset printing or high quality photographic prints for framing. Take for example our 4 Megapixel image, if we convert its resolution to 300 dpi the images size becomes 19cm x 14cm , it has the exact same amount of pixels but each pixel is now much smaller (300 of them in a square inch).

What is a PIXEL?
The most important information to learn first is the basics of how a Digital Camera converts an image to computer code that can be viewed and printed on a computer. Firstly the image travels through the lens of your camera to a sensor called a CMOS sensor. The CMOS sensor breaks the image up into a series of squares called 'Pixels'. Each pixel has its own code that has information on its position and its color.

What is dpi, ppi ?
The image has two distinct ways of determining its size. Firstly the 'size' of each pixel is measured by how many pixels fit in an inch. Digital cameras generally shoot images at 72 ppi (72 pixels per inch) This is called the images 'resolution'. This term is also referred to as dpi (a printers term meaning dots per inch). Secondly the Image has a physical size which is measured by the number of pixels for instance 2272w x 1704h. At a resolution of 72 dpi this image is 31.5inches by 23.6 inches, or 80cm by 60 cm.

What is a Megapixel?
A Megapixel is 1million pixels, so if we take our image of 2272 x 1704 we get 3,871,488 pixels which is nearly 4 Megapixels.
What is file compression? JPEG vs RAW
Most Digital cameras by default save the image as a JPEG file which uses a mathematical algorithm to reduce the physical size of the code inside the image file. Let me explain a little more. If you take a shot on your Digital camera with the setting set at 'RAW' your camera will create a much larger file than the normal jpeg file. Basically the computer code for each individual pixel is stored in the file. This means the image file is of very high quality and all the information is preserved. JPEG files on the other hand are much smaller, but use a formula that groups pixels together and radically reduces the amount of information in the file. In doing this the image is being compromised in its quality. This is not a problem if you intend to reduce the file in size, view the file on a screen or use the file on the Web. But if you intend to use the image for high quality printing, either in a book, brochure or a framed print then I recommend that you shoot the image with your camera set on 'RAW'.

What is RGB Color?
Nearly all digital cameras save the image they shoot as an RGB file. RGB stands for Red Green and Blue. These are the three colors used by computer screens, televisions and projectors. They project these three colors onto the screen to create a very wide spectrum of colors and shades. Because screens use projected light they have a high degree of luminosity and brilliance which enables you to see many colors and shades that cannot be reproduced as easily when printed on paper. The reason for this is that light reflecting from a printed surface (even a glossy one) has no where near the same luminosity as projected light. That is why many people are disappointed when they can't seem to print what they are seeing on the screen.

What is CMYK Color?
CMYK stands for Cyan (light blue) Magenta (pinky red) Yellow and the K stands for Black. These colors are used by standard Offset printers to print nearly all the books and brochures, flyers etc. Laser printers and basic Ink jet printers also use these colors, but today are using increasingly more colors to try and reproduce images more faithfully. Artists sending work to a printer to be published should convert their images to CMYK. Not all photo editing programs support CMYK, naturally programs like Photo shop, and Corel Photo Paint do. There is also an excellent Plug in available for The GIMP which allows you to convert files to CMYK and also adjust the color in CMYK. It is much easier to adjust colors in an image using CMYK rather than RGB.

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