DigitalImaging Basics

An ASMP "Strictly Business"Seminar white paper
by Scott Highton



Digital technology has become a hot item in the business of photographyin recent years. It is something new in an industry that has changed verylittle since its inception. Digital is hot, it's sexy, it's cool, it's new.Photographers and the rest of the visual communications industry are jumpingon the bandwagon in a frantic effort to keep from being left behind.

The reality of this technology is that it's simply a new tool to helpus do things we've been doing for years more efficiently. In its currentstate, it is painstakingly slow, relatively expensive and only just reachinga practical level. It is important, however, to not dismiss it as just anotherfad or trendy style that the photo industry throws at us yearly.

The creation of surreal photographic effects or the seamless compositingof one photo into another may be an "in" trend for the moment,but digital technology goes far beyond that. It is easy for those of usheavily invested in film-based photo equipment, who have established ourcareers by being good photographers, to panic at the idea that we will nowhave to buy thousands of dollars of new equipment and completely changethe way we do business. It is even easier for us to ignore the technologyand assume that it's only a passing fad, like light painting or tilted horizons.

Digital technology represents a major change in the way we deal withinformation. It promises to make communication and information processingfar more efficient than most of us have imagined. The changes it bringsto the business of photography are only a reflection of the changes it isbringing to our lives in general.

This does not, however, mean that we must all go out and immediatelyinvest $30,000 to $50,000 in computers or digital cameras. It doesmean that we need to educate ourselves about the technology and understandhow it can be used in both our clients' and our own businesses.

We will not presume to teach you everything there is to know about digitalphoto technology here. There are dozens of seminars and workshops whereyou can learn intricacies of particular applications. Rather, we will giveyou an overview of digital technology as it relates to photography, so youwill have a basic understanding of pixels, bits and bytes, which will enableyou to determine for yourself what directions to proceed.

Before delving too far into the following information, understand thatdigital imaging, by it's very nature, involves a certain amount of math.Very little of this is actually necessary for the photographer or digitalimager to understand in detail. Most digital imaging systems are designedto make their mathematical functions transparent to the user. However, inorder to realize both the potential and the limitations of digital technology,the photographer will need to understand a few basic math concepts.

If the numbers or formulas presented here seem excessive, skip over thosesegments and try again later. It will be important that you understand themeventually, but it is better for you to learn what you can, rather thangiving up because some high school algebra trauma haunts your past. If youcan calculate f/stops, shutter speeds and can handle inverse square lightingrelationships, you can learn this. Besides, the old joke is that the onlymath a photographer really needs to know is how to multiply and divide bytwo, and that Profit = Income - Expenses.



Digital technology encompasses many areas of the traditional photographer'sbusiness. It can allow us to record our photographs electronically, ratherthan on traditional silver-based film. It can allow us new power and flexibilityto control the content of our photographs, whether originated on film ornot. It can provide us with greater control over the access, usage and distributionof our images. We can make submissions, even to overseas clients, withinhours or minutes, not days. It enables us to distribute unlimited copiesof our images as perfect as the originals. It can eliminate the dangersof losing originals as they move to and from our clients. It is openingup new markets and new types of work for us to explore. It also presentspotential threats to the copyrights and licensing of our images.

There are three basic components of digital imaging: Input, Processingand Output. Input involves a digital camera or scanner which actuallyconverts light patterns (what we've traditionally recorded on film) intodigital data or numbers that computers can work with.

Processing components are the computers or other electronic systems thatwe use to manipulate the digital data, whether it be color correction, compositing,sharpening or even preparing for storage.

Output components are the printers, film writers, printing presses andrecording devices that we use to once again display the images. These devicesconvert the numbers of the digital data back into images that we can viewwith our eyes.

Storage might be included as a fourth component. These would bedevices such as computer hard disks, CDs and other such elements of computer"memory" which allow us to store digital data for processing oroutput at another time.


The Basics

Digital data is a numeric representation of tangible information, whetherit be the colors and shapes in a photograph, audio pitches and tones, text,numbers, calculations, graphic illustrations or combinations of them all.

In digital imaging applications, photographs are broken down into minuteelements known as pixels. They are similar to the individual dotsthat make up a halftone for a printed photo. Pixels have also been likenedto individual grains in silver-based film. Although the analogies are lessthan perfect, they do illustrate the concept in a way most photographerscan relate to.

Each pixel is identified by its two dimensional location in the imageand by the color it represents. The more pixels contained within an image,the greater the resolution and the more digital information available.

If a digital image contains only a few hundred pixels, the resolutionwill be quite low and the image may not even be recognizable. There is simplynot sufficient information available for us to make sense of the result.Even with several thousand pixels, we still may not be able to recognizethe image, but as we increase the number, we increase the resolution anddetail that we can see.


Pixels andImage Resolution

400x267 pixels of 8-bit grayscale = 104 Kilobytes or 104K


 12x18 pixels grayscale = 216 bytes 24x36 pixels grayscale = 864 bytes
 48x72 pixels grayscale = 3.4K 96x144 pixels grayscale = 13.5K


The numeric representation of digital data is done using a binarysystem, which consists simply of ones and zeros. Each 1 or 0 is referredto as an information bit. Simply put, bits work like light switches,which are either on or off at any given moment. One is on, zero is off.The bit is the foundation of digital information. For the photographer,one bit of information at a particular point (pixel) in a photographwould mean that that point is either black (no color = off) or white (fullcolor = on).

By combining groups of these bits together to represent a single pixel,we are able to represent levels in between the extremes of white or black.If we combine two bits to represent shading or color, we can represent four(2^2=4) different light levels (0-0; 0-1; 1-0 and 1-1). Thus, instead ofhaving only black or white available, we add two levels of gray in between.

If we group three bits together to represent a single pixel, we haveeight (2^3=8) combinations possible. They would include black, white andsix levels of gray in between.

With eight bits per pixel, we get 256 possible combinations (2^8=256).This is the standard for current digital imaging systems. Using grayscale(also called "two-tone" or "black & white"), eightbits of information allows us to represent 256 levels of gray per pixel,which is quite adequate for photorealistic representation of black and whiteimages.


Color Levels:Grayscale bit depth

Full grayscale: 8-bit black - 256 levels

 1-bit black: 2 levels

 2-bit black: 4 levels

 3-bit black: 8 levels

 4-bit black: 16 levels


Coincidentally, eight bits of information is known as a byte incomputer jargon. A byte is the amount of computer memory required to representone pixel of 8-bit grayscale information in a digital photo.

Including color information in a digital image requires more data foreach pixel. Using the standard RGB (Red, Green, Blue) color model, mostvisible spectrum colors can be created by combining different amounts ofthe primary additive colors ­ red, green and blue. Computer monitorsdisplay these colors by combining 256 levels (8 bits) of each of the threeprimary colors (totaling 24 bits of color per pixel).

For each pixel, if you have only one bit of information per color, youcan represent eight colors (2^(1*3) colors = 2^3 = 8). These would be asfollows:






































If we had two bits per color per pixel, we would get four brightnesslevels for each of the three colors, giving us 64 possible color combinations(2^(2*3) colors = 2^6 = 64). This is referred to as the color depthand, in this case, would be referred to as "2 bits per color"or a total of "6-bit color."

Extending this to 8-bits per color, we would have more than 16 millionpossible colors (2^(8*3) = 2^24 = 16,777,216 colors). This again, is thestandard for color digital imaging systems. It is similar to the color renditioncapabilities of film, and is referred to as "24-bit color"or "8 bits per color" color depth.

Higher end digital imaging systems provide even more color depth. Manydigital manufacturers tout the increased color depth of their equipment,claiming 10, 12 and more bits per color. A billion different colors canbe represented with 10 bits of RGB color (2^(10*3) = 2^30 = 1,073,741,824).Sixty eight billion colors are available with 12-bits per color (2^36).Keep in mind however, that this increase in color information results ina corresponding increase in computer memory and storage required to workwith the digital files. Even with today's high end desktop computer systems,24-bit color files can get extremely large, demanding lots of expensivecomputer memory and long processing times for even the simplest operations.

With memory and storage concerns in mind, some manufacturers of inputdevices (digital cameras, film scanners, etc.) build their equipment toscan or "capture" the image with more than 24-bit color and then"optimize" it to 24 bits. These systems can recognize billionsof colors, but when storing the image file, save it with the "best"16 million colors.

If this seems a bit confusing, don't worry. Even an experience photographiceye will have difficulty telling the difference between a 24 and a 32-bitimage, particularly since most systems use the 8-bit difference for theinternal calculations required for compositing and special effects. Letthe equipment manufacturers worry about the technical aspects and pixelprocessing algorithms. Consider simply that the range of colors which canbe rendered by traditional transparency film is very similar to the rangeof 24-bit color on a computer.


Storage and Memory

Recording or manipulation of digital data requires that we be able toperform calculations and record the numbers representing the image pixels.This requires computer memory, or computing power and storage capability.

As an example, let's consider a digital image measuring 1,000 pixelswide by 1,000 pixels high, with each pixel containing 24 bits of color information.This gives us a total of 24 million bits of information (1,000 x 1,000 x24 = 24 million). Computer memory and storage are generally measured inbytes, so with 8 bits per byte, our image requires 3 million bytes of memory.

If this image is black and white (grayscale) rather than color, thenthe memory or storage required is only 1/3 of that of a similar color image.A color image would require eight bits of information per pixel for red,green and blue, whereas a grayscale image needs eight bits of only one color(black). Thus, a 1,000 x 1,000 pixel grayscale image contains 8 millionbits of information (1,000 x 1,000 x 8) and requires only 1 million bytesof memory.

A kilobyte (KB) is equal to 1,024 bytes, and a megabyte (MB) is equalto 1,024 kilobytes. (Kilobytes are often abbreviated as "K", suchas "an 800K file" and megabytes are often called "meg",as in "it's saved as an 18 meg file.") Therefore, our 1,000 x1,000 24-bit color image would be a digital file of 2,930 KB or 2.86 MB.This will be important later when we look at the usability of digital files.

In general, the larger a digital file is, the more detail it containsand the larger it can be successfully reproduced.



One of the benefits of digital data is the fact that it can be perfectlycopied. Since a digital photograph is a long series of 1s and 0s, duplicatingthese number strings with a computer is quite simple. Every copy of a digitalphotograph can be as perfect as the original. There are no inherent contrast,grain, sharpness or color shift problems that we encounter when duplicatingon film.

This obviously has advantages for photographers, because it allows usto submit digital files to clients without our original images ever leavingour offices. Since digital data can also be transferred over phone linesand electronically, we can transmit our images directly with our computersand modems or by utilizing online networks.

This ability to make perfect copies can also work against us. Unscrupulousindividuals who may want to copy our images without permission can do sowith ease once they have a complete digital file. There are ways to controlthis, however, which we'll discuss later. Computers are very good at keepingtrack of things and filing detailed information. It is relatively simpleto keep what amounts to a digital paper trail, which tracks the historyof a digital file. There are also data encryption and watermarking schemesthat can offer some protection of digital images from unauthorized use.

Traditional color reproduction is both an art and a science. For decades,it has required experienced technicians in prepress and printing houses.Every press is different, as is the performance of different inks on differentpapers. Knowledge of separation, screen angles, dot gain, trapping, screenresolution, under color removal, registration and a plethora of other concernsparticular to the print business have been required for successful printjobs. Suffice it to say that photographers haven't really concerned themselveswith most of this, since prepress and production firms have dealt with itin the past. However, more of this work is now done on the computer desktopand a basic understanding of how the process works becomes more importantfor photographers.

Black and white printing is relatively simple, as it only requires oneink (black) and one impression of a printing plate on the paper. Reproductionof a black and white photo requires that we use a halftone screen, whichoptically converts the subtle gradations and tones of a photograph intosmall dots. The larger the dots, the more ink goes on the paper and thedarker that portion of the image prints. Likewise, the smaller the dots,the lighter that part of the image prints.

Printing resolution is dependent primarily upon the frequency or numberof dots representing the image ­ just as the resolution of a digitalimage is based upon the number of pixels available.

Halftone screens are available in many resolutions and are measured inlines per inch (lpi). For our purposes, lpi and dots per inch (dpi) areessentially the same thing. Typically, newspaper reproduction is done withan 85 to 100 line screen. Most magazines use 133 lines, while books areusually printed at 150 or more lines.

Converting data from the pixels of a digital image into a line screenfor reproduction is relatively simple, at least for computers. Most pagelayout and image manipulation programs include this utility. However, itis important for the photographer to understand the relationship betweenthe amount of data in their digital files and the amount required to reproducetheir images on a printing press.

If you have too little information, or too few pixels, the printed pieceshows jagged edges and the individual pixels become visible to the nakedeye. If you have too much information, you wind up wasting unnecessary processingtime and put undue demands on the prepress systems, which usually costsmoney. Thus, it is necessary to know what the size and resolution of thefinal output is before you can determine how much information you need inyour digital image files.

The first rule of thumb is that you will generally want about twicethe resolution that you will need for your output. This is not an absolutefigure by any means. In fact, some experts claim you need as little as 1.25times. You can experiment for yourself, but for our purposes, we'll assumethat we need 2 times the resolution (called a "sampling"or "scaling" factor).



If we want to reproduce a black and white photograph sized to 4"x 6" in a typical magazine, we can calculate the digital file neededthrough the following formula:

2 x screen resolution (lines/in.) x reprod. height
x 2 x screen resolution (lines/in.) x reprod. width
= file size (bytes)


(2 x 133 (lines) x 4 (inches))
x (2 x 133 (lines) x 6 (inches))
= 1,698,144 bytes (1.6 MB)


Thus, we would need a file size of 1.6 MB. This would be an image containing1,064 x 1,596 pixels (8-bit grayscale). If we were reproducing the samephotograph in color, we would need to triple the file size, because we wouldneed this same amount of information for each of the three RGB colors (24-bitcolor).

1,698,144 bytesx 3 colors = 5,094,432 bytes (4.9 MB)


Notice how our required file sizes change when we change the reproductionsize or resolution. If we size the same photo to 3.5" x 5"(a rough equivalent to a 1/4 page photo in the typical consumer magazine)instead of 4" x 6", we get the following:

Black & white:
(2 x 133 x 3.5) x (2 x133 x 5) = 1,238,230 bytes (1.2 MB)

(2 x 133 x 3.5) x (2 x133 x 5) x 3 = 3,714,690 bytes (3.5 MB)


If we increase the reproduction size to 8.5" x 11" (fullpage or cover bleed), we'll require a far greater file size:

Black & white:
(2 x 133 x 8.5) x (2 x133 x 11) = 6,615,686 bytes (6.3 MB)

(2 x 133 x 8.5) x (2 x133 x 11) x 3 = 19,847,058 bytes (18.9 MB)


Note that if we lower the screen resolution to an 85 line newspaper level,the file size for the same 8.5"x11" reproduction decreases toabout 40 percent of that required for the magazine resolution:

Black & white:
(2 x 85 x 8.5 ) x (2 x85 x 11 ) = 2,702,150 bytes (2.6 MB)

(2 x 85 x 8.5 ) x (2 x85 x 11 ) x 3 = 8,106,450 bytes (7.7 MB)


This information is important when we are acquiring the image in digitalform, whether it be from scanning a film image or shooting with a digitalcamera. The size and resolution of the digital file limits our successfuluse of it.



   Scaling Factor = 2


File Size:

 File Size:


 (85 lines)

 (100 lines)

 (133 lines)
Photo CD Master:     
Base/1624K72K128 x 192

.8" x 1.1"

.6" x 1"

.5" x .7"
Base/496K288K256 x 384

1.5" x 2.3"

1.3" x 1.9"

1" x 1.4"
Base384K1.1MB512 x 768

3" x 4.5"

2.6" x 3.8"

1.9" x 2.9"
Base x4 1.5MB4.5MB1024 x 1536

 6" x 9"

5.1" x 7.7"

3.8" x 5.8"
Base x166MB18MB2048 x 3072

12" x 18"

10.2"x 5.4"

Pro Photo CD:     
Base x6424MB72MB4096 x 6144

24" x 36"

20" x 30"


Double Density Disks:    
Grayscale 800K  739 x 1109

4.3" x 6.5"

3.7" x 5.5"

2.8" x 4.2"
Color RGB  800K 427 x 640

2.5" x 3.8"

2.1" x 3.2"

1.6" x 2.4"
High Density Disks:     
Grayscale 1.4MB  978 x 1466

5.8" x 8.6"

4.9" x 7.3"

3.7" x 5.5"
Color RGB  1.4 MB 564 x 847

3.3" x 5"

2.8" x 4.2"

2.1" x 3.2"

1) Reproduction sizes are approximate.
2) Maximum sizes on floppy disks will actually be slightly less than thefull capacity of the disks.


Many people will make the mistake of scanning or acquiring every imageat the highest possible resolution, thinking that it's better to have toomuch information that too little. While this approach does provide moreoptions for the use of an image, there is little point to having to dealwith a 72 MB file when you're only reproducing it as a 2"x3" photoin a black and white catalog. The excess data demands more computing power(read $$$), more memory, more storage space and slows down every step ofthe computing process. Pushing pixels around in a digital file is slow enoughas it is, even with today's fast desktop computers. There is little pointin making these systems work harder (and slower) by demanding millions ofunnecessary calculations.

Sometimes, you may want to reverse the above calculations in order todetermine what size you can successfully reproduce a given digital image.For instance, a high density floppy disk can hold almost 1.4 MB of data.How large could you reproduce a file that size in a newspaper or magazine?Let's start out printing a color image in a standard magazine:

 Area of printed image = Bytes÷ (2 (scaling factor)
÷133 (line screen)) ÷ (2 ÷ 133) ÷ 3



To convert MB to bytes:
1.4 MB x 1,024(KB/MB) x 1,024 (bytes/KB) =1,468,006 bytes

1,468,006 bytes÷ (2 ÷133) ÷ (2 ÷ 1333 = 6.9 sq. inches (approx.2.1" x 3.3")


If this is a black and white (grayscale) file, then we use the same formulabut don't divide by the three RGB colors. Thus:

1,468,006 bytes÷ (2 ÷133) ÷ (2 ÷ 133)= 20.7 sq. inches (approx. 4" x5")


If we change the printing screen resolution to 85 lines (newspaper),we can print the image files as follows:

1,468,006 bytes÷ (2 ÷85) ÷ (2 ÷ 853 = 16.9 sq. inches (approx.3.5" x 4.8")

1,468,006 bytes÷ (2 ÷85) ÷ (2 ÷ 85)= 50.8 sq. inches (approx. 6" x8.5")

So just like most other aspects of photography, everything is a tradeoff.If we increase resolution, we decrease reproduction size. Reproducing colorrequires three times more data than black and white. The better or largerwe want to display our work, the more digital data we need.



Digital data, particularly from digital photo files, can be reduced involume through a variety of mathematical algorithms or compression schemes.These systems, which have acronyms such as JPEG, ADCT, LZW, MPEG, etc.,all reduce the numbers in a digital file into more efficient equations thata computer can store in a smaller amount of memory. Some are called "lossless,"which means that there is no loss of quality or data in the compression/decompressionprocess. Others, which compress files into the smallest sizes, are called"lossy." Generally, the more a file is compressed, the more informationis lost and the greater the degradation of the image.

For those who use lossy compression schemes, the tradeoff in qualityis usually worthwhile because of the value of reducing the file size. Somecompression schemes can reduce file sizes by almost a 30:1 ratio, with littlenoticeable loss of image fidelity. For the user who needs to store largeimage files in small spaces of computer memory, or who needs to transmitimages over phone lines, the advantages are obvious. Using a 9,600 baud(bits per second) modem, an 18 MB image file would take almost four anda half hours to transmit over a phone line. Compressing the image file reducestransmission time, and the dollar savings are often worth the relative lossesin quality.

Compressed images need to be decompressed before they can be opened orused again. The decompression process replaces the data that was lost inthe compression of the file with the exact data that was removed (lossless)or with estimated data (lossy). For the most part, photographers don't needto be too concerned with the complexities of compression, except to understandthe difference between lossless and lossy systems.


Photo CD

In 1990, Eastman Kodak introduced Photo CD, a system that can store digitizedphotographs on a 43/4" diameter compact disk (CD). There are currentlya number of Photo CD formats, and the technology has become an industrystandard. Basically, Photo CD is designed to allow the scanning and digitalstorage of film-based images at a relatively low cost. Although originallytargeted for the consumer market with the hopes that consumers would wantto look at family snapshots on TV, it has yet to be widely accepted there.However, the photographic, publishing, computer and communication industrieshave embraced it wholeheartedly.

The Photo CD Master format can store up to 100 scanned images at fivedifferent resolutions each (called an "Image Pac"). It uses aproprietary technology (Photo YCC) developed by Kodak and stores the equivalentof 1,800 MB of photo digital data on each 600 MB compact disk. Each "ImagePac" includes five different resolutions of the same image. A sixthresolution is available on the newer and more expensive Pro Photo CD format.


Photo CD ImagePacs

DescriptionPixelsFile SizeUse (Kodak described)
Base/16128 x 19272KThumbnails & index use
Base/4256 x 384288KLow resolution preview, FPOs & comps
Base512 x 7681.13MBViewing on standard TVs and monitors
Base x41024 x 15364.5MBProposed HDTV resolution
Base x162048 x 307218MBFull resolution (35mm), almost full page magazine reproduction
(Pro Photo CD)  
Base x644096 x 614472MBMedium format and 4"x5" film scans, high resolution reproduction


While many other manufacturers sell scanning and photo digitizing equipment,Photo CD is important to mention because of it's relatively low end-userprice and because it is now a standard for both the distribution and storageof digital photo files. Although the Photo CD Image Pacs can only includethe above resolutions, Kodak has designed the format so the resolutionsavailable meet most user needs, including those of traditional publishingand the newly developing multimedia fields.

Hundreds of Photo CD service centers are available throughout the country,which can scan 35mm film images (both slide and negative) for between $1and $2 each. Compared with desktop publishing service bureaus that chargebetween $10 and $25 for similar scans, the price break is significant. Additionally,the storage media (the CD) is usually included in the price of Photo CDscans. With service bureau scans, you generally have to provide your ownSyQuest cartridge ($50 - $100) upon which you can only store a few 18 MBimages.

The difference between these services is that the Photo CD centers haveinvested $100,000 or more in PIW (Photo Imaging Workstation) equipment andare dealing in high speed and high volume scanning, whereas other servicebureaus tend to use desktop scanners in the $2,000 - $20,000 range and workat a lower, more specialized volume. There are advantages to both, althoughservice bureau prices have fallen dramatically since the arrival of PhotoCD.

Since Photo CD has become an industry standard, stock agencies, softwareand clip art publishers, online photo networks and most of the publishingindustry have adopted it for storage and electronic distribution of theirimages. Using Photo CD files requires little more than a desktop computerwith a CD-ROM drive and low cost software from Kodak. (Popular digital imagingsoftware packages, such as Photoshop, generally also include access to PhotoCD files).

Photo CD base resolution provides sufficient data for full color, fullscreen display of the photos on most televisions and computer monitors.Base x 16 resolution is adequate for 8"x10" reproduction in mostmagazines ­ almost a full page. In fact, Kodak has claimed that basex 16 resolution contains the same amount of picture information as manyof its 35mm consumer films do.



In 1985, the United States Office of Technology and Assessment (OTA)released the results of a survey about America's perceptions of right andwrong when it came to copying the work of others. The report, entitled "IntellectualProperty in an Electronic Era," indicated that 70 percent of the generalpopulation thought it was acceptable to copy other people's work. Fortypercent of the American business population did, too.

The report also said that "public relation strategies (to counterthese practices) are likely to be most effective if they focus not on therights of copyright holders, but on the relationship between the copyrightholder and the users of the work. Messages about unauthorized copying maybe more effective if they emphasize the ongoing value of a partnership betweencreators and users."

Copying and unlicensed use of photographs have been made far simpler,and the quality of such reproduction has become far better with the adventof digital technology. Once a digital file leaves the photographer's possession,it can be copied repeatedly without any loss of quality. This presents athreat, particularly those who distribute high resolution digital fileson CD-ROM or via online picture services.

However, the traditional methods of photographer self promotion ­sourcebook ads, promo pieces and reprints ­ are even more vulnerableto theft due to the tremendous quality and availability of desktop scanners.There have been hundreds of cases reported where clients simply scannedan image from a photographer's printed promotion piece and published itwithout ever needing original film. Desktop scanners and digital imagingsoftware make it relatively simple to acquire any image electronically,to enlarge it, sharpen it or alter it if necessary.

While unauthorized use of photographs has always been a problem, thefact that it is so much easier today means that unscrupulous types havean easier time committing their crimes. Even more of a concern is that 40percent of people in business and 70 percent of the general population aren'teven aware that it's not OK to copy our images.

There are however, ways to protect our work. One unsuccessful method,which a number of CD producers and online providers mistakenly trust, isto only provide "screen resolution" or smaller data files. Thesedistributors believe that their files are small enough that they can onlybe reproduced at sizes less than two inches square. Their assumptions arebased on the same formulas that we used earlier.

The standard computer screen displays images at 72 dpi, or a total of640 x 480 pixels. For a 24-bit color image, this is a 900 K file. PhotoCD base resolution is 512 x 768 pixels, resulting in a similar 1.12 MB file.Using the formulas listed earlier with a scaling factor of 2 and a standard133 line screen for a consumer magazine, we get the following:

Screen resolution (640x480 pixels):
bytes ÷(2 ÷133) ÷ (2 ÷ 133) ÷3 = 4.3 sq. inches (roughly 2.5"x 1.75")

If we take this same file and change the scaling factor to 1.25 (whichsome experts use), we can increase our reproduction size over 150 percent:
921,600 bytes÷ (1.25 ÷133) ÷ (1.25 ÷133) ÷ 3 = 11.1 sq. inches (roughly 3.8"x 2.9")

This is getting close to the size of a 1/4 page magazine ad. If we usethe same formula on a Photo CD base resolution file, we get a 4.7"x 3" reproduction.

Furthermore, most software applications like Photoshop offer the abilityto do data interpolation, which expands the size of the digital fileand fills in the data between the original pixels with with similar data.A variety of interpolation algorithms are available and, when used withunsharp masking and other sharpening algorithms, can successfullyexpand the usable dimensions of a digital image up to 400 percent (or 16times the file size).

Thus, in a worse case scenario, if an end user were to take our original"screen resolution" file, use a 1.25 scaling factor and quadruplethe dimensions of the image, they would wind up with a 14 MB file and couldreproduce it 15.4" x 11.5" in size ­ almost a two-page spreadin most consumer magazines. Using the more common scaling factor of 2, thisfile could still be reproduced 9.6" x 7.2" in size ­ closeto a full page. Fractal-based interpolation algorithms currently under developmentpromise even greater interpolation amounts.

It is also important to note that the new electronic markets, such asmultimedia and other electronic uses, only require a maximum of screen resolution(640x480 pixels), since they will only be used for display on televisionand computer monitors. Delivering a screen resolution file (900 K or PhotoCD base) to an electronic or multimedia client is the equivalent of deliveringoriginal film to a traditional print client.

Once again, it is not necessary for photographers to commit this mathto memory. Rather, it is important for you simply to understand that thetechnology to reproduce and improve your "low resolution" digitalimages is readily available, and that "low resolution only" isnot sufficient protection against unauthorized use.


Better Security

One method of better protecting digital images is to use a combinationof watermarked and encrypted image files. The watermark, such as a largecopyright © symbol, is a semi-transparent overlay on the "preview"or screen resolution image, which allows the viewer to see the entire imageclearly, but makes it impractical for publishing. Generally, a watermarkedimage will be accompanied by a "clean" image in another file,which is data encrypted so it can't be opened without passwords. This allowsthe photographer to submit preview images to clients with a watermark embedded,and then if the client decides they want to use the image, they can agreeon a usage fee over the phone with the photographer, who then provides thepasswords to unlock the "clean" encrypted file.

While it is possible for an experienced Photoshop user to remove thevisible watermark from the preview images, it would take a number of hoursto do yet would still only result in a screen resolution image. Thus, it'sgenerally cheaper for a user to buy the needed rights and get passwordsfor the encrypted file, which is usually large enough to be reproduced upto 1/4 page. If larger reproduction is needed, the photographer can sendfilm. It's not a perfect system, but it keeps the honest people honest,and makes it very clear that the digital photos are not provided as clipart or free-use images.

One criticism of this system has been that art directors and clientslooking at lots of pictures, feel that the watermarks are distracting anddegrade the quality of the images. They argue that when scanning hundredsof thumbnail sized photos on a computer, the visual distraction of the watermarkdetracts from an image. They say they are less likely to choose a watermarkedimage over a similar unmarked image. Whether this criticism is valid dependsupon whom you talk with, but it has been expressed as a concern.

A more recent advance in the watermark arena is the Digimarc invisiblewatermarking technology, which introduces a virtually indistinguishable(to the human eye) pattern of identifiable noise into the pixel patternsof any digital image file. This noise pattern can be detected with Digimarcreader software, and can survive duplication, halftone screening or colorseparation and reprinting of an image. It has tremendous potential as acopyright protection tool in the digital world for photographers and othervisual artists, and allows protection of the images without the distractionof a visible watermark. This technology was introduced in 1996 and was incorporatedthat year into industry standard software packages such as Photoshop 4.0and CorelDraw7. Digimarc, Portland, OR

One of the great promises of the Pro Photo CD format was to be its abilityto store encrypted high resolution image files. However, Kodak has yet toinclude this ability because they've not received National Security Administration(NSA) clearance on their encryption scheme. The NSA requires that any encryptionsystem available in a product that might be used outside the U.S., be clearedby them, as part of their responsibility to protect national security.

It is critical to keep a photographer's credit, copyright notice andreference information with their photographs once those images have beenstored as a digital file. Many software programs provide text filesto accompany digital images. In the various text fields, data about eachphoto, including copyright notices, captions, photographer, file number,model release and much other information can be stored. These text fieldsare generally used for database searches, particularly by online pictureservices and electronic stock agencies. Unfortunately, the text files areeasily stripped away from the digital image when the files are opened withsoftware other than that used to create it. This is a very common occurrence.

It is therefore, critical that the photographer's name, copyright noticeand a source ID be included as part of the bitmapped image of photosstored for electronic distribution. This can appear as a credit bar aboveor below the actual image area. It can still be cropped out by the end user,but it at least offers more assurance that they will see and note the copyrightinformation before using the image. Digital files are opened and re-savedby clients as many times as traditional film is handled by individuals.The copyright information must be kept as part of the digital image data,just as a copyright notice remains on the slide mount for a piece of film.



Digital Paper Trails

Another advantage to digital technology is the fact that computers aredesigned to deal efficiently with countless minute details that would drivehumans nuts. This includes cross referencing of files and the automaticrecording of transaction data. This can be a boon to picture professionalsconcerned about tracking their images.

It is relatively simple to create data files accompanying our digitalimages that include information about the photos. This can include caption,exposure, copyright, publication history, sales price or electronic transmissioninformation. Essentially, we can create electronic information trails forour digital images, which are far easier and faster to use than paper records.

Most online picture services use such practices. They can keep trackof who previewed what images on their system, what choices they made, howtheir search pattern worked and what their preferences were. Also, theycan record how the picture was downloaded or sold, what the usage was andwhat keywords the buyer used to search for it. Profiles of clients can bedeveloped based on their past choices ­ whether they prefer their sunsetsto be orange or red, in the upper left or lower right of the frame, whetherthey prefer horizontals or verticals. All this information can be used bythe photographer to better understand his or her markets, and can also beused to track image files.

Of utmost importance is the fact that digital technology brings the needfor new clauses in photographers' delivery memos, estimates, contracts andother forms. We must clearly state what rights are being granted and forhow long, particularly in uncharted multimedia waters. Some photographersinclude clauses that prohibit any electronic alteration or scanning of theirimages without prior written permission. All should specify that the clientwill destroy, erase or return to the photographer any digital files thatwere created from the photographer's work. This prevents future unauthorizedreuse (accidental or not) by the client and is just as appropriate as requiringthat the client return original film after their contracted use.



There is a great deal for all of us to learn with the new digital toolsavailable to us. There are several basics, however, that are important tokeep sight of:

1) Digital technology is not a passing fad. It represents a majorchange in the way our collective business and personal lives are run. Itshould not be ignored.

2) It is not necessary for any of us to rush out and blindly jump intothe digital world. Investing thousands of dollars into new computer equipmentor digital cameras without first understanding the needs of our own businesses,can be suicidal. Many of us may never even need to touch a digital cameraor scan a piece of film. What is necessary is that we understand the basicsof how the technology works ­ that we stay informed about how our clientsare using it and what their needs are. This information will help us makeour own decisions and help us run our businesses appropriately.

3) Technology changes fast. What is state-of-the-art today, may be obsoletein six months. Do not fear the changes, because technology improves throughchange. Be aware. Stay informed. Make your decisions based upon the bestinformation available at the moment.

4) Most importantly, don't lose sight of why you became a photographer.Our business still requires us to be visual communicators, and creatinginteresting, informative and inspiring images is the basis of that work.Don't get sidetracked into becoming a techno-weenie and lose sight of whyyou are a photographer. Be creative. Make good pictures.

...And enjoy what you do.


 ©1994 Scott Highton
All Rights Reserved

Reproduction of any portion of this volume requires written consentof the author.




The following formulas are also useful for file size and reproductioncalculations:

1 Kilobyte = 1,024 bytes
1 Megabyte = 1,024 Kilobytes = 1,048,576 bytes


To calculate required file size for a particular reproductionsize:

Color (24-bit) images:
File size (bytes) = (Scaling Factor x Linescreen x Reproduction height) x (Scaling Factor x Line screen x Reproductionwidth) x 3

Grayscale images:
File size (bytes) = (Scaling Factor x Linescreen x Reproduction height) x (Scaling Factor x Line screen x Reproductionwidth)


Other file size formulas:
1 pixel = 1 byte (grayscale files)
1 pixel = 3 bytes (24-bit RGB color files)

Total pixels in image = pixels in lengthx pixels in height
Area of reproduced image = length x height


To calculate maximum reproduction size of a file:
Area of printed 24-bit color image = bytes ÷(Scaling factor ÷ Line screen) ÷ (Scaling factor ÷Line screen) ÷ 3

Area of printed grayscale image = bytes÷ (Scaling factor ÷ Line screen) ÷ (Scaling factor÷ Line screen)

Max. length of reproduced image= pixels in length ÷ Scaling Factor ÷ Line screen
Max. height of reproduced image = pixels in height ÷Scaling Factor ÷ Line screen



Bonus formula for techno weenies:
Suppose you have a digital file of a certain size and you want to determinethe maximum reproduction length and width (not just the area or productof the length and width, but the individual length and width measurements).Assuming you only know the file size and the format of the original (35mm,6x7, 4x5, etc.), along with your line screen frequency for reproduction,you can do it as follows:

1)Calculate the area of your printed image as described above.

2)Determine the height to length ratio of your original. Examples: 35mm =2/3, 6x6 = 1, 6x7 = 6/7, 4x5 = 4/5, etc.

3)Length of printed image = Square root of total printed image area (1)÷ square root of height to length ratio (2)

4)Height of printed image = Total printed image area (1) ÷ lengthof printed image (3).

Your local service bureau has provided you with 14.8 MB scans (24-bit RGB)of your recent prize-winning 6x7 color transparencies, which were used foran awards program. You want to reproduce the photos again as part of yourown promotion calendar for next year. Knowing that your calendar separationswill be done with a 150 line screen, what are the dimensions of the largestreproduction you can do from each of these digital files?

Convert MB to bytes:
14.8 MB x 1,048,576 = 15,518,925 bytes

Calculate area of printed image: (Scaling factor = 2)
1) Area of printedimage = 15,518,925 bytes ÷ (2 ÷ 150) ÷ (2 ÷150) ÷ 3 = 57.5 square inches

Calculate max. length:
6x7 image = 6/7ratio

3) Reproductionlength = square root of 57.5 ÷ square root of 6/7 = 7.58 ÷.92 = 8.2 inches

4) Reproductionheight = 57.5 ÷ 8.2 = 7 inches

Total reproduction size = 8.2"x 7"
(6x7 cm original scanned as 14.8 MB file printed with 150 linescreen)