Hello everyone. My name is Aleks Davidovich and I'm very excited to be here today to work through some of the more common image preparation and handling issues facing artists and photographers, particularly as they relate to selling reproductions of their work online (read: prints).

While it's common for many artists to use an online marketplace like EBAY and Etsy to sell their original artwork, our focus here today will be on helping those of you who have already digitized your work (for the purpose of selling print reproductions), to get the most from your high resolution digital images.

I won't be getting into the actual process of digitizing your artwork other than to say it's almost always a good idea to have it done professionally. This is particularly true for artists with larger physical originals more so than it is for a photographer working with transparencies, let’s say.

Scanning or photographing large pieces of art requires specialized equipment, precision, and optimum lighting conditions that are very difficult for the average person to achieve. Selling professional quality prints at its core, requires good input, or in other words - very high quality digital images. I'm sure everyone here has heard the expression "Garbage in Garbage Out", and it's important to realize that it could not be more relevant here.

As well, even with photography one should consider that the final output size of a print will ultimately be limited by the available size and resolution of a digital file.  For example, an original photographic work, or even a photo of a painting with a 10 mega pixel camera will only yield a file around 3872 x 2592 pixels.  We’ll get into the subject of resolution in a minute, but basically, a file that size would only facilitate a print of about 38x25 inches MAX.  Using even a "prosumer" grade scanner on your film negatives has a very similar limit.  So get your work professionally captured - it’s worth the investment.

Therefore our discussion assumes you're already in possession of high quality images, and so we will begin with where to go from there. Let’s get started!.

I've broken this presentation down into three topics that always seem to be at the forefront of our own customers' questions. We’ve decided to leave out the fourth topic which was to be Simple Image Correction since this really deserves its own live presentation. These topics are:

• File Formats and Image Quality
• Resolution and Image Size
• Color Management Basics

Each of these topics plays an important role in ensuring the success of your print reproductions and it's my aim today to dispel some common myths while providing everyone with a rounded overview of the important elements regarding each one. I say rounded because I want to keep the less experienced users involved without confusing them with high level terminology, while focusing on the key points to understanding and working well with your digital files.

As much as possible I will provide images to illustrate some of these points and will be relying on Photoshop CS2 as the primary example image editing software application. Those of you using other image editing software should still be able to use most of these principles in your work flow.

As always, I'll run through the presentation in its entirety and then open the floor for a Q&A session afterwards where you can ask more directed questions, and I will do my best to answer them!

File Formats and Image Quality

So first of all let's begin by discussing what we mean when we talk about digital images. What is a digital image? Quite simply a digital image is an electronic file that is a visual representation of something.  There are two main categories of image files: "Raster" and "Vector" files.  We’ll touch on both, but start with raster images.

What is a raster image file you ask?  It is a technical name for the type of image file you are likely most familiar with. It is an image file that visually represents something by using a finite amount of dots otherwise known as pixels or rasters. These pixels are the building blocks that collectively make up the image as we see it on screen and ultimately on print.

Pixels can also be explained as tiny squares of light and color that get stacked together both vertically and horizontally and are assigned a dark to light value between 0 (solid black) - 255 (pure white) to represent the image or picture. Unlike traditional film media which is a purely continuous tone process, digital imaging and printing relies on these dots or pixels to create the illusion of continuous tone both onscreen and in your output to print. I mentioned that there is a finite amount of these pixels or rasters, but we'll touch on that a little later when we discuss resolution: the size and/or frequency of these building blocks. We'll also compare rasters to vectors to illustrate how scaling can impact the quality of your image. Now that we've defined what an image file is, we'll talk about some of the different file formats that raster images can exist as. The most common image file formats used today are:

• JPEG
• TIFF
• PNG

We’ll go through these one by one and explain some of the pros, cons, and correct usage of each.

Perhaps the most common and widely used image file format used is JPEG. In fact, most all digital cameras today output image files as JPEGs by default. For those who are interested, JPEG is an acronym for "Joint Photographic Experts Group" and is simply a form of image compression created to reduce the file size of digital images.  JPEGs are compressed image files. We'll get into that in a minute.

In contrast, TIFF files are also image files but are "uncompressed" images meaning they store all the data in an image.

PNG files are image files that use compression algorithms but in a "lossless" manner, meaning they uncompress back to their original quality.  Usually a PNG file is best used with a specific type of image, such as one with limited colors, as it will create a smaller file size (in MBs) than a TIFF, but retain all of the images information.

These file formats are often referred to as either "lossy" or "lossless".  This simply means that a file type will either lose some information as it is created, or ultimately keep it.  A similar subject, but not the exactly the same, is compression.

So What is Image Compression? The primary difference between these three types of files is in the way they store data and more importantly, how much data they store. JPEG's as I mentioned above use file compression to reduce file size. File compression essentially looks at an image and either removes data that is duplicated or has little value to the image or saves it in shorter form.

For example if you had an image that had large blocks of solid red, only one pixel of that color red would be saved along with all the other locations of the color. When the image is displayed or "uncompressed" it would apply that bit of data to all the red areas in the image. The degree to which data is discarded of course depends on the quality selected which many of you already know it is possible to specify when saving as a JPEG. Higher quality equals less compression and vice versa. Here is an example of an original image (top) which we've saved both as a high quality & low quality JPEG.

As you can see the image to the left has little compression and shows smoother gradations or transitions between colors and highlights/shadows… the image on the right was saved with lots of compression resulting in a small file but an image that is not suitable for printing. Along these lines, I should point out that another primary caveat to using JPEGs is that JPEG compression suffers from generational loss meaning that every time a JPEG file is opened and re-saved it degrades further and further. This is less noticeable if you always work with the highest quality JPEGs but can manifests itself when printing at larger sizes. What file types should you be using? Ultimately, one should look at what the destination or use is for an image. For most people, JPEG's are simply the smarter choice. They are great when you are trying to conserve space on your hard drive or when you want to email them to friends. They look great on-screen and will even look good in print if the image is of high enough quality.

Photographs tend to look better as JPGs than more graphical images, as they have a range of tone.  Graphical images with large areas of 1 or 2 solid colors can be misinterpreted by JPGs and thus may be more suited for PNG files. However if professional print quality is the ultimate goal, TIFF files are probably what you should be working with. While TIFF's can be extremely large files sometimes exceeding 500MB or more in size, they will faithfully reproduce all of the information or DNA stored in your image to print and especially do not suffer from generational loss like a JPEG.

As an alternative, or if sending huge files across the internet doesn't work for you, one could build their workflow around TIFF files with the final version being exported as a JPEG, saving that JPEG with the highest quality setting (12). Using this model, all image editing is done in a lossless environment with compression added only to the final version of the file. OK... Moving on...

Resolution and Image Size

Resolution is perhaps one of the most confusing and misunderstood topics related to print production. I know from personal experience at Imagekind, that it is one of the more popular questions that we get. It generally goes something like this: "I want to upload images to my gallery but I need to know what resolution you guys require"? For reasons that I will try to describe below, this is quite literally an impossible question to answer with a blanket response. You see, image resolution is directly dependant on output size... so here we go… While resolution can be used to describe display devices like a monitor or TV (screen res), our focus here is on IMAGE RESOLUTION and its impact on PRINTED OUTPUT. We're going to talk primarily about pixels and their relationship to resolution. Previously I had mentioned that images are comprised of a finite amount of these pixels which collectively make up the images we see. This concept is particularly important to remember as we discuss resolution. Simply speaking, image resolution is a term used to describe the number of pixels present in a unit of measurement. As our focus is on print production, the unit of measurement for most of us on this continent is inches. Otherwise known as PPI or pixels-per-inch, it is the primary measure of image resolution relative to its output size or print size.

Remember now that because there are only so many pixels present in a given image, the effective resolution of an image will change as you alter the desired output size for your prints. For example, increasing the output size (of your print) will simply redistribute the same number of pixels over a larger area and DECREASE your print resolution. Conversely, reducing the desired size of your print or document size, will pack those pixels closer together increasing your print resolution. I'll illustrate this in a  minute. Now, quite often people like to refer to resolution as DPI or dots-per-inch. While most people generally understand the inference, it is technically incorrect. DPI is a term used to define the resolution of printed output (your prints). It is NOT a measure of image resolution (PPI).

While we now know that images on screen are created with pixels, it's important to understand that printers use dots to re-create images. On an inkjet printer these would be dots of ink and in the case of a laser printer these would of course be dots or particles of toner. Either way, as modern printers are capable of producing dots far smaller than a pixel, DPI should always be higher than PPI. I almost can't stress this enough -- Once people begin thinking about their images in terms of pixels and in particular pixel dimensions, resolution begins to make perfect sense. Let's look at a couple examples to illustrate what I mean here.

Here is a screen shot of an image I opened in Photoshop.

For those that use Photoshop and want to follow along at home simply right click the link below and choose "save link as" to save it locally on your computer.

Next open file in photoshop and select image > image size or using the shortcut alt+ctrl+I on the PC ( Mac: Command+Option+I) we pull up the image size dialogue box.

Now let’s examine some of the important elements here and how changing any of them affect the resolution of an image. The things we'll be looking at in particular are:

• Pixel Dimensions
• Document Size
• Resample Image

First let’s make sure we're all looking at the same thing here. Making sure that re-sample image is unchecked, let’s begin by looking at image size at the top. We can see that we have an image size of 2592 X 1944. These are the dimensions of the image expressed in pixels.

Notice too that these numbers at the top are not editable at this time. This is because we've asked Photoshop to not re-sample our image. Any changes we make to the image can only affect output size and of course resolution.  Take a look also at the second area called document size.  Currently this image is sized to be 14.4" wide by 10.8" high at a resolution of 180ppi. Now watch what happens when we increase resolution.

step 1: Change resolution to 300 PPI step 2: Notice that the document size has gone down to 8.64"x6.48".  Our image size at the top has not changed however. So why did this happen? Well it happened because there is a direct relationship between the two. As image resolution goes up, output size goes down. If I could point to one thing when talking about resolution it would be to "know the difference between Image Size (pixel dimensions) and output size (document size). These are two wholly distinct specifications.

Again, I apologize to those of you who already know this but feel it's important enough to emphasize because many folks don't understand the difference. Now... we have, of course, done these modifications with the re-sample box unchecked. What if we had left it checked and boosted the resolution even higher? More importantly, what does it mean to "re-sample" your images?

Well, we'll illustrate this below but in short: leaving the re-sample box checked in effect tells Photoshop that you would like to change the number of pixels present in your image.

For instance, if we chose to reduce the value for resolution, we'd essentially be asking Photoshop to reduce the number of pixels in the image. If you opted to increase the value for resolution, well then you'd be asking Photoshop to "re-sample" or create new pixels in your image;  AKA scaling up.

This sounds ok until you consider that doing so is a software process that can only guess what those additional pixels should look like. Though this process can actually be done successfully in small doses, I'd like to take this opportunity to discourage this practice unless you are an experienced Photoshop user. Ok... here's the links....

step one: with resample checked, change resolution to 500 (a bit extreme but I want to illustrate the point.) step two: observe changes in pixel dimensions.  I now have dimensions of 7200x5400 - nearly 300% bigger.  Note also that my document size hasn’t changed.

Here is a look at the image after scaling zoomed to 100%:

We can clearly see the effects of re-sampling or scaling in the image.  It now contains excessive noise and the beginnings of pixilation.  We no longer have crisp separations of color and smooth tonal gradations.  This is a direct consequence of up-sampling and asking photoshop to create new pixels.

Scaling images is something that is perfectly fine for Vector art ( there's that word I mentioned earlier) but something that requires restraint when dealing with raster or image files. I know I promised you a comparison and here it is. Raster files rely on a finite number of dots to create an image while Vector files use points to create the same image. This may sound confusing but check this out: This is an image file containing three circles. 

(1.) The top left is an original circle created as a vector.   (2.) The bottom left is that same circle resized as a vector.  Notice the points surrounding the shape.  As I transformed this shape and scaled it to a larger size, the points simply relocated themselves and redrew the circle according to my scaling - with all the relevant data in-tact.

(3.) Doing the same thing with the image on the right, which a rasterized version of the original circle, I can clearly see the effects of scaling this raster image - artifacts and noise that were not in the original circle.  Photoshop has had to guess how to apply the new pixels and though it did a reasonable job, closer inspection shows that the image has suffered.

I don't mean to beat this point into the ground but just want to make sure you see what I mean.

So what are these rules and how do we control this process? I won't be getting into color management in a hard core way but rather will focus on the following three areas:

• Calibrating devices
• Colorspace information
• ICC profiling and Softproofing

Calibrating DevicesAll professional labs utilize specialized tools to measure and calibrate the devices that collectively make up the digital imaging chain. Each device can be thought of as a link in this chain and include things like scanners, monitors and printers. Calibration devices simply measure each devices ability to display light and colors.

For example, using a colorimeter one would measure the ability to display color ranges, brightness, and contrast for a given monitor, and ultimately create a monitor or display profile that we would then associate with the device.

Doing so would ensure that as we work in color, we are viewing as accurately as possible the true colors and tonal gradations present in an image.

Now I realize most of you don't have this type of equipment laying around but will offer two suggestions to help you in your quest towards a color-managed workflow. One: Pantone offers an inexpensive calibration device called the Huey which I believe retails for somewhere around $100. While not as sophisticated as an X-Rite Optix, it is still a worthy piece of equipment for a lot less money that will at least put you on the right path. Two: If you just don't want to purchase a calibration device, there are two simple changes you can make to at least control how you view colors onscreen - brightness and color temp.

LCD monitors by default are way brighter than they should be and it's important to bring the levels down to around 60-70%. Second, color temp on monitors is generally set to 9300k which is a pleasing cool white temp. That temp tends to make things brighter and well cooler on screen.

The problem is that it is not an accurate reflection of how things look in natural daylight. Changing your monitors temp to 6500K will more closely replicate natural daylight conditions.

Colorspace Information

Color space is simply a set of numeric values that describe the ability to display a range of colors. Since devices differ in their ability to show colors it's important to know their limitations. Monitors for example, have a limited range of colors they can display while printers can generally show a much wider color range.

When talking about color space it's important to first understand the basic types or modes of color. We'll focus on RGB here but mention CMYK for comparison. RGB is an additive color space meaning it uses and mixes light to create colors. It is also the colorspace used by monitors and display devices. RGB assigns and stores values of red green and blue in individual channels. CMYK is a subtractive color space and is used for printers. It describes what colors of ink are necessary so that light reflected off the inks and paper create the colors that we see. Knowing that we will primarily be living and working in an RGB world let’s begin talking about the different spaces or profiles and how we should be using them. sRGB is a color space that was created specifically for monitors or display devices. It is very commonly used, and in truth is perfectly fine for most people. In fact, and because, web browsers are not color managed when displaying images on the web, it should be the color space you use to accurately show colors on the web.

Adobe(1998) is another fairly common color space used primarily by graphics professionals because it has a wider color gamut meaning it can show a broader range of colors. I'll be illustrating this visually for you in a minute. Whichever color space profile you choose to work from is up to you.  What is important is that you properly record this information with all your images so that the next link in the imaging chain knows what to do with the color information in your image.

How do we do this? Simple - whenever you work in an image editing application, like Photoshop, you have the option to save or record color space information.

Select "save as" from the file menu and look down to the part of the dialogue box called color. There should be a line entitled ICC profile and a check box next to it.

It just so happens that this particular image had sRGB assigned to it and we're now making sure that this information is saved in the image. If you're using Photoshop, there's an even easier way to make sure you're always doing this. I'll show you how to set up your own custom work space in Photoshop where you can specify your color space preferences and color management policies.

I'll describe the steps now and if you want to follow along at home in Photoshop you can.

By selecting edit > color settings - we pull up a dialogue box or palette that allows to specify several things.

First you'll notice that in settings I've got Aleks Workspace. This is a custom workspace that I created previously and use as part of my everyday workflow. The next section called working spaces contains the color space information for each mode that I may be working in.

For the purposes of this discussion we really only care about RGB, but you can see that I've got a selection for each category. My default color space happens to be Adobe (1998), and I've spelled it out here.  This means that every time I create a new image in Photoshop I will be doing so in this color space.

Next, we see color management policies. This part is important. You can see that I've chosen to always preserve the embedded profile for each mode.  This means that when you open an image whatever information is locked up in the image will be preserved and faithfully reproduced.

And finally the check boxes below this spell out what to do when a profile is missing from an image or does not match the default color space. I would recommend that you always tell Photoshop to prompt you in these situations.

For example, if an image you are trying to view does not contain a profile you would want to know that in advance and take steps to make sure you apply the correct the color space before saving. Ok.. I'm getting a bit long winded here. But we're almost done. ICC Profiling and Softproofing ICC (International Color Consortium) Profiles describe the color attributes of a particular device or viewing requirement. As we mentioned above, they can describe the characteristics of a display device.  However what I really want to talk about now is profiling for output devices or printers.

Have you ever tried to print pictures to your printer at home and wondered why the colors were all wrong? Well, the reasons can vary, but ultimately the problem most likely occurred because there simply wasn't any information about both the device you were printing to or the paper you were printing on.

This is where ICC Profiles come in and are the final link in the color management chain. Using another calibration device called a Spectrophotometer, we can measure a printers ability to display color and contrast to a given type of media. Once measured, we simply save the information to a profile which would then be used every time a print is sent to that particular printer and paper. Here is what it looks like:

You can see in this picture that we have a ton of little color squares or targets that we've printed on the particular media we're profiling. Once they are printed we simply measure them with the spectrophotometer to give us values for each color. These values are stored in the new ICC Color Profile which will be created once we're done measuring. This measurement is done because printers and the paper that you print to vary widely in their ability to show color and gradations.

For example, inexpensive matte poster paper generally has the ability to show a decent amount of tonal range but lacks the color punch and Dmax (the ability to show black blacks and shadow detail) of a coated photo paper. Likewise, we would need to build a profile that spells this out specifically. I promised a visual representation of color space or profiles. Here it is:

This screenshot is of a color mapping software application that shows the ranges of a particular color space or profile. We can see that Adobe (1998) has a larger gamut or range of color than sRGB.

I've also included an output profile here to illustrate how this paper can handle the colors that we see on screen.  The paper profile is of premium photo luster.

SoftProofing

Finally, the very last link in the chain before printing is Softproofing.

Softproofing is simply a  way to take a an ICC profile for a particular type of media that you wish to print to and apply it visually in Photoshop to get an approximation of what the print will look like.

This proofing relies on the numeric values for light and color previously measured, and applies them to the image, allowing you to preview what areas of the image could be affected by the limitations of the paper and printer.