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FAQ's
The team you hire to produce your web or print project is as important
as the equipment and materials you choose. So, when it comes to digital
imaging, it is vital to hire professionals who are able to pay close
attention to your interests and requirements–especially in the area of
color control.
Here are questions you may have about getting the most from your
digital images. I hope my answers will help you create top level
projects.
*Why don’t colors reproduce accurately?
Entire books and college courses are devoted to the headache–I
mean--challenge, of getting colors accurately reproduced in digital or
film format. Every photographer has wrestled with this relentless
problem. During each step of the workflow, from lighting to capture to
layout and print, there are many ways for objectionable color casts to
enter the process. I will focus on several common ways that color
problems can affect the digital image.
Light
The color control process
should begin with the control of lighting during the photo shoot. When
a photographer uses traditional film, he or she must carefully match
the light source with the type of film in use. Your photographer should
use color-correcting filters alongside test shots. This is especially
important when flourescent, incandescent and high pressure lights come
into play.
Although digital cameras
are easier to use with all light sources, care must still be taken to
produce accurate colors. That’s why photographers often use a test card
like Macbeth Color Checker or a Kodak gray scale.
Scans
If your image is on slide
or transparency film , it must be converted to digital format with a
high quality scan. Since this can be a complicated task, it should
ideally be performed by a professional with a high end scanner. Feel
free to call me for information about some quality pre-press labs I
recommend to help you with this step.
Computer color
adjustments
An important tool in color
control is the computer. However, the computer monitor can create
problems because each one shows varying degrees of color, brightness
and contrast. When a monitor is properly calibrated to a standard,
images can be more accurately adjusted. Software is available to
calibrate your monitor. Here are some links to web sites that will help
you calibrate and offers hints on what you may need to do:
http://epaperpress.com/monitorcal/
http://www.photofriday.com/calibrate.php
Knowing that every monitor
is different means that images viewed on the web will look different to
each viewer. There’s not much you can do about this, except to keep
this in mind.
File conversions –
RGB to CMYK
Most digital image files
are in a three color format called RGB (Red Green Blue) which
corresponds to the colors of light in a computer monitor. If the image
is destined for print, it usually needs to be converted into CMYK (Cyan Magenta
Yellow Black) which corresponds to the ink colors needed to print a
photo. Usually a graphic designer is responsible for this step in the
work flow. Something to keep in mind is the next step in printing.
Because every print method and press is different, CMYK output will
vary based on the printer. A proper CMYK file may print fine in one
process, but not in another.
Another step you may wish
to take is to create profiles (called ICC profiles) that match your
computer, monitor and output devices (like printers) to control color.
ICC profiles provide a way to insure consistent color. These files are
specific to each device on your system and contain information about
how that device produces color. Get a profile for your monitor,
printer, scanner, digital camera or other equipment. Many of these
profiles are available for download from the web. This may get you
involved more than you wish, but learning about it helps you to
understand what’s needed in color control. For more information and an
introduction to ICC, check out this site:
http://www.color.org/faqs.html and http://www.color.org/iccprofile.html
Print
The printer must control
color too. There are many kinds of printers nowadays and each will
handle the color in a different way. There are many choices and
adjustments to make at the printing step that can affect the color.
Find a quality print professional who you can trust and ask advice.
It’s always a good idea to receive a proof--a sample of what the final
product will look like–and comment on it.
Unusual color problems
Certain natural and
man-made colors and dyes can cause problems. For example, some colors
in minerals and clothing dyes sometimes just don’t show up properly on
film or digital camera sensors. I remember having this trouble with
some green marble tile and fabric luggage. My solution to this problem
is to alter the image in the computer from a digital file. [[DAN, WHO
ALTERS IT? THE PHOTOGRAPHER?]]]
Kodak has a helpful
technical publication on this subject at:
http://www.kodak.com/global/en/professional/support/techPubs/e73/e73.jhtml
*What digital file format should I use?
Several popular digital file formats are available. Jpeg, gif, Tiff and
bmp are the most common. There are digital camera specific raw camera
file formats. Here is a brief description of each:
TIFF
files are preferred by the printing industry. They are a bitmap kind of
file and are usually not compressed. Most graphics programs that use
TIFF do not use compression. Therefore, file sizes can be quite large.
Sometimes a lossless compression algorithm called LZW is used, but it
is not universally supported.
JPEG
files are the most common web/electronic file in use. They are
optimized for photographs and continuous tone images that contain very
many colors. Under some conditions, JPEGs can achieve amazing
compression ratios even while maintaining very high image quality. JPEG
works by analyzing images and discarding kinds of information that the
eye is least likely to notice. It stores information as 24 bit color.
Note: Each time you save a JPEG image, it discards more information!
The more times you save a file, the more information is discarded. Even
renaming a file can discard important information.
Important: the
degree of compression of JPEG is adjustable. At low compression levels
of photographic images, it is very difficult for the eye to notice any
difference from the original, even at high magnification. Depending on
the nature of the original file, compression factors of more than 20
are sometimes acceptable. Better graphics programs, such as Paint Shop
Pro and Photoshop, allow you to view the image quality and file size as
a function of compression level, so that you can adjust the balance
between quality and file size.
Not all JPEG
files are the same! Some with high compression may be suitable for a
web site, but will be totally unacceptable for print. Some of the
discarded information in the file is very important for good print
quality. Though some designers and printers may carefully work with
“Hi–Rez” JPEGs, it’s generally better to use TIFFs or another
uncompressed file to avoid complications down the road.
GIF
files create a table of up to 256 colors from a pool of 16 million. If
the image has fewer than 256 colors, GIF can render the image very
closely. When the image contains many colors, software that creates the
GIF uses any of several algorithms to approximate the colors in the
image with the limited palette of 256 colors available. Better
algorithms search the image to find an optimum set of 256 colors.
Sometimes GIF uses the nearest color to represent each pixel, and
sometimes it uses "error diffusion" to adjust the color of nearby
pixels to correct for the error in each pixel.
GIF achieves
compression in two ways. First, it reduces the number of colors of
color-rich images, thereby reducing the number of bits needed per
pixel, as just described. Second, it replaces commonly occurring
patterns (especially large areas of uniform color) with a short
abbreviation: instead of storing "white, white, white, white, white,"
it stores "5 white."
Thus, GIF is
"lossless" only for images with 256 colors or less. For a rich, true
color image, GIF may lose"99.998% of the colors.
GIF images are
usually reserved for logos, type or simple graphics on the web.
Camera RAW
uses the digital file that comes directly from the camera image sensor.
Think of camera RAW as a digital negative. It often looks rather ugly,
but actually contains a maximum of information–way beyond what a
monitor or print can show. It needs image processing with image
software like Photoshop after capture.
The disadvantage
is that there is a different RAW format for each manufacturer. Many
graphics programs are unable to read the proprietary RAW files.
I shoot almost
completely in Camera RAW (Nikon NEF) format and then process the image
to JPEG or TIFF.
For more details and specific information on file sizes and compression
I recommend DISC (Digital Image Submission Criteria):
http://www.disc-info.org/
Here are links to
further reading on the subject of file types:
*What size image file do I need for my print or web project?
This is a common question, but the answer can be complicated. A lot
depends on the fineness of your printing line screen and the size of
the image on the page. For a starting point use this chart provided by
DISC (Digital Image Submission Criteria):
http://www.disc-info.org/resources/DISCBrochure_v9.pdf
*Can I enlarge the digital file to fit the layout?
Usually increasing the image size causes a lot of problems especially
with image sharpness. Sometimes the image can be enlarged if great care
is taken. There are some software products that do a decent job of
this. Two of these are Nik Sharpener and Genuine Fractals. In any case,
you must start with a high quality original file.
It’s always best to start out with a file that exceeds your
requirements. Reducing the image size usually causes no problems.
If you have more questions or need more details, please contact Dan
Stultz. dan@stultzphoto.com
630-231-9010
dan@stultzphoto.com
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