Part 12 - From Pixels to Print

We know what pixels are. We also know that the camera doesn't produce a picture but instead a data file that describes the specific amounts of the primary colors (red, green and blue) for every pixel that comprises the picture.

So, if we really don't have a picture, how is the picture displayed on our computer monitor and then as an image from our inkjet printers? Key to understanding these technological miracles is remembering that there are two ways of reproducing the visible spectrum:

• By using the three additive colors (also called primary) -- red, green and blue -- in nearly infinite density combinations to replicate all visible colors
• By using the three subtractive colors (also called secondary) -- cyan, magenta, yellow -- in finite density combination to reproduce all visible colors.

The iDarkroom uses both methods:

• The computer monitor displays images using the Primary Colors -- red, green and blue.
• The inkjet printer produces images using the Secondary Colors -- cyan, magenta and yellow (and adds a black ink to provide contrast and a truer black than can be produced by man made cyan, magenta and yellow inks together).

Click here to review my earlier post Color Primer for more details.

The following graphic borrowed from Wikipedia is the best illustration I have found to help understand monitor vs. printer methods of creating an image as well as the relationship between pixel's per inch (PPI) and dots per inch (DPI):

Each grid represents a 10 by 10 pixel area of a much larger multi-million pixel image

Starting with the monitor

The data contained in the original image file is saved in terms of red, green and blue per pixel (a value between 0 and 255 for each primary color). As shown above, a typical sRGB computer monitor is capable of displaying all 256 values of red, green and blue at each pixel location. At 256 x 256 x 256, this means each pixel can display all 16.7 million colors that a typical DSLR's image sensor is capable of recording.

This display approach is straightforward. The only additional math or adjusting of the monitor that must be done (via the ICC profiles used by your image editing program) is to take into account the color space of the original image file. If you've set your camera, for example, to use the Adobe RGB color space, the computer will adjust the pixel color values to present the correct Adobe RGB colors on the RGB monitor.

Moving on to the inkjet printer

The "original image file" to "inkjet print" relationship is more complex for several reasons:

• Inkjet printers use the secondary colors to reproduce the visible color spectrum -- cyan, magenta and yellow. So, RGB values contained in the original file must be converted to secondary colors as well as to the color space of the printer/paper combination.
  
• Inkjet printers place "dots" of color on paper, but these dots are limited to the color cartridges in your printer. In today's photo inkjet printers, this typically means 8 different colors. For example black, photo black, matte black, cyan, light cyan, magenta, light magenta, and yellow are used by many entry level photo printers.
• Printer resolution is expressed in terms of the number of "dots" it can place within one inch. Dots-Per-Inch (DPI).
• Inkjet "dots" of ink are necessarily much smaller than a pixel. (Explaining why printer DPI numbers are so much larger than the PPI of the image file.) This is critical since the "dots" of ink can only be one color and one density. In order to provide the illusion of continuous tone, tiny dots of ink are placed in extremely close proximity to each other to provide the subtle shades of color required in a photograph.

In fact, the dots placed on paper by an inkjet printer are so small and so close together that our eye cannot distinguish the individual dots and colors without considerable magnification. Our brain visually blends these areas to produce a shade of color. (Much the same way modern military camouflage blends and marries into the surrounding natural colors to become part of the background.) The right hand portion of the illustration above reveals that only secondary ink dots are present and that there are many, many "dots" of secondary color in each pixel area. The higher the DPI, the more dots a printer can produce per inch and the more detailed and continuous the printed image appears.

Once again, the multiple variables involved in the process of creating a print -- camera, to monitor, to final print -- are apparent. And, once again, it's obvious with all the necessary conversions and adjustments taking place behind the scenes that -- even if we make NO image adjustment of our own -- unless the entire workflow is calibrated and in control, the odds of any picture being an accurate reflection of the original scene are slim.

But knowing what's happening throughout the workflow and taking the necessary steps to calibrate your iDarkroom are the first steps to stunning prints.

If you have any questions or comments, feel free to pass them along.

Part 4 - Calibrating The Photographic Workflow

You get up in the morning. Take a shower. Brush your teeth. Eat breakfast. Read the newspaper or your on-line news feed. Get in your car. Go to work. Do those things at work that bring home the bread. Get in your car. Drive home. Eat supper. Play with the kids. Watch TV. Go to bed. And it starts all over again the next morning. This daily routine (which varies only slightly from day to day) can be likened to the recent photographic catch phrase -- workflow. When something disrupts your daily workflow, like a car that won't start, not only does your workflow change, but you are forced to take steps that will return your routine or workflow to its normal status.

A photographer's digital imaging workflow might go something like this:

1. Take the picture.
2. Download the picture to a computer.
3. File the image in a digital cataloging/editing program (for example, Adobe Lightroom or Apple's Aperture).
4. Perform necessary image editing/enhancement (this could be the same program used for cataloging or specialized editing software like Adobe's Photoshop or LightZone by Light Crafts).
5. Make prints or digital files as requested by customer.
6. Deliver prints or proofs to customer.

Like your personal daily workflow, if any single component is "out of synch" in the photographer's workflow, time and materials are wasted to solve the problem before normal production can resume. In the photographer's workflow components falling "out of synch" are often the result of color management issues.

Calibrating the components of a photographer's workflow is the first step towards higher productivity, fewer final print surprises and profitability. Nothing burns up a photographer's profit quicker than endless reprinting to achieve the results he/she and the customer expects. As you are discovering, quality ink and photo-quality paper represent a large portion of your iDarkroom expense.

So, how do you minimize these expenses? It starts with an understanding of the variables that were presented in the previous posts and a calibrated production system.

This post begins a discussion on calibrating the first and most important window into your photography -- your color monitor. To be intentionally blunt: If you don't calibrate your computer's monitor, the chances of making a final print that matches your monitor is in the same realm as winning the state lottery. Well... probably not that good.

You saw from my airplane TV monitor example that exactly the same monitors from the same manufacturer produce entirely different color images. Time changes all things. But you know this. That's why you take your car in for a check up every 3,000 miles or so. To bring it back as close to factory specs as possible.

Why would a color monitor be any different?

Monitors are even more touchy than your car. The accuracy of a color monitor (calibration) should be checked at least once each month.

There are methods of visually calibrating your monitor, but a dedicated hardware device is more accurate and reliable. Fortunately, a variety of monitor calibrators are available with prices for every budget. X-Rite’s Huey® color monitor calibrator is shown below attached to the monitor of an iMac®. Investing in a good monitor calibrator is essential to accurate color management. If your computer and monitor are your first iDarkroom purchases, then make a monitor calibrator your SECOND purchase.

X-Rite’s Huey® Color Monitor Calibrator is an inexpensive starter device to calibrate your monitor and ensure more accurate color rendition on your computer display. (The calibrator is the black rod in the center of the display.)

Monitor calibration is a straightforward and very quick process for bringing the monitor back to its original specifications. This monitor "tune up" is accomplished by the calibration software that comes with the calibrator. A small file is created at the end of the process that allows your monitor to display colors correctly. This file is called an ICC Profile and will be discussed in the next post.

Although there is disagreement among printer manufacturers, I believe the same routine color calibration is needed for printers. Printers are mechanical devices and are subject to wear and tear that invariably has an impact on color consistency and predictability. I no longer work for Hewlett Packard, but I have become a firm advocate for printer calibration. The current Photosmart B9180 and B8850 13"x19" pigment printers from HP have built-in color calibration capabilities. I believe printer calibration will become a standard user feature in the future.

Whatever you decide, the printer is the third of the essential purchases for your iDarkroom. Watch for my post on the basics of ink jet photographic printers.

With the monitor and printer calibrated, the next post, Part 5, will cover those little files that control how color is displayed on your monitor and reproduced on your printer.

As always, if you have any questions or comments, you know where to find me.