From Pixels To Paper
With digital cameras proliferating, your customers could use a little guidance on how to pick a model that takes photos suitable for offset reproduction.
by Rick Reed
Due to the growing popularity and recent availability of inexpensive digital camera technology, University of Missouri-Columbia Printing Services receives many inquiries from our customers concerning the choice of an adequate model.
The most common concerns for color images captured with digital cameras arise from the issues of image resolution and color space. The confusion centers around the inherent differences between two media: commercial printing and the World Wide Web.
While offset printing requires 300 ppi (pixels per inch at actual printing size) images, which are saved in the CMYK color space as TIFFs, Web images only require 72 ppi and are generally saved in the RGB color space as JPEGs.
RGB And JPEG Files
Digital cameras generally produce native RGB/JPEG files. This is because RGB is a large color space and generally captures the color detail adequately for most color images. JPEGs are used as a file format because of the high compression rate, which dramatically saves disk space and transfer times. RGB/JPEG files also work well as Web graphics.
Why aren't RGB/JPEG files used in offset printing as well? The answer comes from the basic differences in the media. Web graphics are viewed on our computer screen, which is composed of hundreds of thousands of picture elements, which in turn are each made from tiny red, green, and blue light sources. By varying the intensity of these red, green, and blue (RGB) values for each pixel, almost any visible color can be reproduced. This process adds the red, green, and blue light in the viewer's eye and is therefore called the "additive" color model.
A printed page does not have glowing pixels however. It can only reflect the light that hits it from an external light source. This light is generally white, like the paper, and must be filtered through ink to reproduce different colors. In this process, all the colors except the desired ones are removed from the white light, allowing the desired ones to enter our eyes. This "subtractive" model uses four basic ink colors: cyan, magenta, yellow, and black (CMYK). By combining these "filters" through the application of CMYK inks, a large number of the visible colors can be reproduced.
Which Camera Do You Buy?
Now back to the big question. Which camera do you buy? The big answer: it depends. You need to know the maximum image size you will want to print.
Measure the height and width in inches, then multiply these measurements by 300. This will tell you the minimum number of pixels in each direction the digital camera you purchase should have. For example: say I know that the maximum image size that I will ever want to print is 8x5˝. Then the camera I purchase will have to capture images at least 2,400x1,500 pixels (i.e. 8 x 300 = 2,400; 5 x 300 = 1,500).
What people find out quickly is that it costs more than they anticipated to get a digital camera that will capture the detail they will need for printing applications. Here are some very rough estimates for digital cameras, comparing printed image sizes to prices (based on prices as of February 2002):
3x4˝: $250; 4x6˝: $300; 6x8˝: $800; 7x9˝: $1,200; 8x10˝: well over $10,000.
To appreciate the cost for very high-quality digital images, consider the special digital back apparatus that can be added to a professional-quality Hasselblad camera. It can capture just 8˝ square images (at 300 ppi) but costs over $30,000—and that is just for the digital back, not the camera and lenses.
Cost Rises With Image Size
As you can see, the cost rises dramatically as you exceed the 7x9˝ range. Because the required area of a CCD (Charge Coupled Device: a chip that measures the light hitting each pixel) array needed to capture larger and larger images grows exponentially, the cost seems to grow at least logarithmically. So even as the lower resolution range cameras become very cheap, the higher resolution range will stay relatively expensive.
Naturally, there are other factors to consider when buying a digital camera, but they go beyond the scope of concern for offset printing. You will want to consider the storage capacity, cost for storage, method and speed of transferring images from the camera to your computer, the optic quality and zooming capabilities of the lens, flash capabilities, shutter speeds, battery life and more.
Rick Reed is electronic prepress anaylist at University of Missouri-Columbia Printing Services.
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