Using QTR to Make Optimal Digital Negatives v3

The QuadTone RIP Manual Using QTR to Make Optimal Digital Negatives Version 3 March, 2009

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The Quadtone RIP Manual: Using QTR to Make Digital Negatives Version 3 Ron Reeder, Mercer Island, February 2009 Table of Contents page Introduction: Why QTR?

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Download, install and print with QTR

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Install a custom profile

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Constants and variables in a profile

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Four steps to making a profile

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Step by step instructions to make a profile

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Making and evaluating a step wedge test print

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Making a gray curve

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Another way to insert a gray curve into a profile

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Tweaking a gray curve

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Ink distribution curves

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Introduction: Why you ought to use QTR for making digital negatives. The Quadtone RIP (abbreviated QTR) is a printer driver that can be used in place of the driver that came bundled with your Epson printer. QTR is the tool of choice for making digital negatives since it offers more control over the process than any other competing system. In this Introduction I will explain why this is so. If you just want to learn how to use QTR, you can skip this Introduction and go straight to the section on QTR downloading and printing. There are three problems to consider when making a digital negative, and QTR offers advantages in solving each of these problems. Negative contrast. The first problem is setting the contrast range of the negative so it matches the range of the emulsion you will be printing on. In QTR this is

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accomplished by raising or lowering the ink limits of the dark inks until ink density in the darkest patch of the step wedge negativeis just sufficient to print as pure white in the final print. Linearization of print midtones. All digital negative systems except QTR linearize print midtones by applying a Photoshop correction curve to the digital image file. This is not optimal since such correction curves invariably result in more or less image degradation. In addition, these correction curves are often rather severe and thus are difficult to fine tune (small changes to the curve result in large changes in the final print). With QTR, print midtones are brought roughly into linearity by raising or lowering ink limits in the printer driver and without touching the digital image file. Final linearization is done with a Photoshop correction curve. But, in QTR this curve is applied to the ink curves, not to the image file. In addition, the correction curve is usually rather mild and is accessible for fairly intuitive tweaking if needed. Balancing inks for maximum tonal smoothness. All printers print all of their inks as dots of close to equal size. For the smoothest possible print tones, it is important that all of the printer’s inks are utilized, and it would be nice if they could be balanced so that they filled in the holes around each other’s dots as completely as possible. In actual fact it is not possible to achieve this ideal with normal Epson inks because they vary so wildly in their ability to block various wavelengths of light. In this Manual I advise treating all the dark inks as if they had equal blocking power by assigning the same ink limit to each dark ink (and doing the same for the light inks). I know this is not true, but in practice it results in very good negatives and simplifies writing QTR profiles. If you are interested, I have described a more rational approach to balancing the Epson inks in an article elsewhere on this website titled “Making a digital negative for printing on variable contrast silver gelatin paper”. The ability to balance inks for maximum tonal smoothness is unique to the QTR approach. I have seen excellent prints made using nearly every available digital negative approach. However, QTR clearly offers the most control for making the optimal negative. It is worth the extra effort required to master its somewhat steep learning curve.

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Downloading, Installing and Basic Printing with QTR To get the most out of QTR you should learn how to write custom QTR profiles, tailored to your emulsion and printing technique. In teaching you how to do this I will use as an example a QTR profile I have written for the Epson 3800 printer designed to make negatives for printing on a palladium emulsion. This profile is called RR3800UCmK-OHP-Pd and is shown in Figure 1. I will go through this profile line by line and explain what each line is for. But first, some basic information about QTR. QTR was written by Roy Harrington to improve the ability of Epson printers to print quality black and white prints. In contrast to the proprietary Epson driver, QTR gives us complete control over the printer’s inks. At some point it dawned on me that it would also give us the tools to print optimal digital negatives. Over a period of several years Roy has generously tutored me in how to use QTR and this manual is the current distillation of what he has taught me. QTR is inexpensive shareware. Download it, try it out, and if you like it, send Roy $50. It is a bargain.

To download QTR go the to Quadtone RIP Overview site (www.quadtonerip.com/html/QTRoverview.html). Under DOWNLOADS click on the latest version of QTR (version 2.6.2 as of this writing). I use a Mac and therefore the instructions in this manual are written for the Mac OS X operating system running Photoshop CS3 (other Photoshop versions work OK but the detailed screen grabs may be slightly different). QTR also runs well on Windows but the user interface is rather different. The Download page of the QTR Overview site has a tutorial written by Tom Moore that describes how to use QTR in Windows. After the download unstuffs you will get a window that has a useful Tutorial pdf (save and read) plus an install-QTR icon. Click on the install icon and follow the instructions that pop up. In version 2.6.2 QTR automatically installs itself in two places. First, a folder titled QuadToneRIP is installed under Applications (Finder>Applications>QuadToneRIP). This folder has several useful things in it, but the most important is the subfolder titled Profiles. Open Profiles and you will see a series of folders, one for each of the printer/ink combinations that QTR supports. If you are

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installing QTR for the Epson 3800 using the Ultrachrome (K3) inkset, open the 3800-UC folder. At the top you will see an icon for the Install3800 command. Click on this icon and QTR will immediately install all of the QTR profiles listed below the Install icon. These profiles are useful for printing regular black and white digital prints with QTR and you should install them, but they are not useful for making digital negatives. HOWEVER, in the future, when you want install a custom QTR profile, you will drag it to this folder, among the other profiles, and click on the Install3800 icon to install the custom profile. To complete profile installation, quit and then restart Photoshop. To check that a profile really has installed, go to Harddisk>Library>Printers>QTR>Quadtone>Quad3800. Under Quad3800 you will see all of the profiles that have been installed for the 3800. Note that the original profiles are textfiles and have the appendage .txt. During installation they get translated into .quad files. If you see your profile in this list with a .quad file ending, then it has been properly installed. (Note that Mac OS has Libraries tucked away in several different locations. The one with the .quad files is the library under the Harddrive icon) To delete a profile go to the list of .quad files and delete the profile from there. (deleting the .txt file from Applications>QTR does not work) The next time Photoshop is closed and then reopened the profile will be deleted. Printing a digital negative with QTR is relatively straightforward. First, edit your positive image file until it looks the way you want (it should be in 16 bit depth and have gray gamma 1.8 embedded in it). Then size the image to the size of the final print you wish to make, flip the image horizontally (so that left and right will be correct in the final print), and invert the positive image to a negative (Image>Adjustments>Invert). Next, open Print Setup (File>Print Setup). Under “Format for” you should now have the option of choosing Quad3800 as the printer driver. Choose the correct media size and orientation and click OK. Now go to Print (File>Print). In Photoshop CS3 this will open the Print with Preview window. In this window, under Color Handling, select No Color Management. All the color management will be handled by our custom QTR profile and we do not want either Photoshop or the Printer to add any extra management. Check that your image is correctly sized and oriented on the page. Now click Print to open the Print Dialog box. In this dialog you will once again have to select Quad3800 as the printer.

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Then, under Copies and Pages select Quadtone RIP. This will open the QTR dialog box which in version 2.6.2 looks like this:

The settings shown are the ones I use when making a negative for palladium printing with the Epson 3800. In the Curve 1 box I choose the particular custom QTR profile I wish to use. With None selected in Curve 2 and Curve 3 the Tone Blending sliders automatically set Curve 1 to 100%. I select Auto Sheet Feed when using single sheet Pictorico. It is very important to set Resolution to its maximum of 2880 dpi. I choose Uni-directional as the speed (although I am told that the newer Epson printers also do very well on Bi-directional). I normally use Matte Black as the dark black ink to save switching back and forth when I want to make ordinary digital prints on matte paper. Select whichever dark black ink you used when constructing the custom QTR profile. Under Advanced Adjustments the Ink Limits and Gamma sliders are not used since we have already set these values more precisely in the custom profile. You might want to play with different dither options. I find it hard to tell the better options apart and usually go with Adaptive Hybrid. Feed in a sheet of Pictorico, hit Print, and you are off to the races.

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How to Install a Custom QTR Profile After you have altered a QTR textfile and wish to install it, be sure it has a legal name, then close and save the textfile. NOTE: You may find that your new profile fails to install. Failure to install can be due to several causes. For example, the title of the profile can contain only letters, digits, underscore or dash. It can have no spaces in it. If you have not exactly followed the rules for typing number pairs into Gray Curve the profile will not install. Trying to figure out why a profile will not install is one of the less enjoyable features of QTR. Drag the icon for the saved textfile into the 3800-UC Profile folder (Applications>QuadTone RIP>Profiles>3800-UC) and double click on the Install3800 icon. A window will open listing all of the profiles currently installed for that printer, including your new profile. In addition, if you have turned on the Graph Curve function in the profile’s textfile, a graph of the ink usage directed by your new profile will be displayed. At this point I often make a screen grab of the ink usage graph so I can study it later. To make a screen grab, simultaneously press the keys Apple-shift-4. The cursor will turn into a small circle with a cross. Place this cursor at one corner of the graph, depress the mouse and drag to the opposite corner. When you release the mouse a snapshot of the selected area will be taken and will appear on your desktop as a .png file. To finish installation of your profile, quit and then restart Photoshop. The new profile should now be present as a .quad file under Harddisk>Library>Printers>QTR>Quadtone>Quad3800 and should also be available as one of the profile options in the Curves boxes of the QTR Print window. If you ever want to un-install a QTR profile the only way to do so is to find the relevant .quad file and drag it to the trash. The next time you quit and restart Photoshop the profile will be uninstalled and deleted. Constants and Variables in a QTR Profile Figure 1 shows the QTR profile “RR3800-UCmK-OHP-Pd”, written for the Epson 3800, using the K3 Ultrachrome inkset with matte Black (mK) as the dark black ink, with the negative printed on Pictorico OHP transparency material, destined to be used for contact printing on a pure palladium emulsion.

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QTR profiles are written as textfiles in a program called TextEdit that comes bundled with your Mac and they carry the file extension .txt. The easiest way to open TextEdit is to double click on a pre-existing QTR profile, then you can delete or type in new text as desired. Most of the lines in the profile consist of an instruction (ie, a function) followed by a number that tells that function how much to act. In writing a QTR profile you will primarily just leave the functions alone and only change the numbers up or down. I have indicated two classes of numbers in the textfile. One class of numbers are the CONSTANTS. There are eight constants and I have named them with BLUE letters as C1, C2, …….., C8. These constants are determined by the particular Epson printer and inkset you are using. You will not change them unless you change printer and inkset. The second class of numbers are the VARIABLES. There are four variables, indicated by RED labels (Actually, the fourth variable is a set of numbers specifying the Gray Curve. More on that later). These are the numbers you will change in writing a new profile. (THE RED AND BLUE NAMES ARE NOT PART OF THE PROFILE. I WROTE THEM IN FOR CONVENIENCE IN DISCUSSING THE PROFILE).

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Figure 1. Textfile for QTR profile RR3800-UCmK-OHP-Pd Four Steps in Making a QTR Profile First Step. Determine the Basic Exposure. This means determining how much exposure is needed, through a sheet of clear Pictorico OHP, to give maximum black on the alternative emulsion of your choice. Once the Basic Exposure is determined it will be used in testing all the negatives you make and it will not be altered. Second Step. Set the Contrast Range of your negative. In the First Step you determined how much exposure is needed to obtain maximum black when no ink is printed on the negative substrate. Now you determine how much ink to lay down so that the darkest patch of your negative will print as pure (or nearly pure) white. You will control the density of the darkest patch by varying the amount of the four dark inks that are laid down (the K, M, Y, and C inks). You will control the dark inks using Variables 1 and 2. Third Step. After the contrast range of the negative is set, use Variable 3 to increase the amount of the light inks (LK, LC, and LM) to the point where you can see some detail in the print shadows. In practice this means that you want to increase Variable 3 until the 90 or 95% step of the step wedge prints as a gray that is noticeably lighter than the pure black 100% step of the step wedge. Fourth Step. You should now be able to derive numbers for a Gray Curve correction curve that will finish the linearization process. The set of numbers that describe the Gray Curve are what I call Variable 4. Step-by-Step Instructions Note that a # sign placed in front of a line of Textfile type turns that line off so that it conveys no instructions to the printer. Lines with a # sign in front are just there for you to make notes to yourself. As notes to myself I like to give the name of the profile, the printer it is intended for, and the inks it will use (including whether it uses matte black or photo black as the dark black ink). In general I use matte black as the dark black ink because in the K3 inkset it is a much better UV absorber than photo black. PRINTER=Quad3800

This line helps QTR install the profile in the correct

printer folder. Type in the correct Quad name for the printer you are using.

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CALIBRATION=NO

This profile is NOT intended for QTR calibration

purposes. GRAPH_CURVE=YES

If you type YES, each time the profile is installed

QTR will also display a graph of how each of the inks is used. This graph is very useful to see (for example, see Figure 6, below). C1

N_OF_INKS=8

7 is the correct number for older printers such as the 2200,

4000, 7600, using the Ultrachrome Inkset. 8 is the correct number for newer K3 inkset printers such as the 2400, 3800, 4800, etc. C2

DEFAULT_INK_LIMIT=100

I set this number to 100 in all cases and then

specify lower inks limits for each ink individually. There are other ways to use this number but this approach is simple and works for me. Let’s skip over the Variables for the moment and continue with the Constants. C3

N_OF_GRAY_PARTS=2

We will use dark black as one of the Gray Parts and

light black as the other Gray Part. All the other dark inks (Y, M, C) will follow the distribution of the dark black ink and the other light inks (LM, LC) will follow the distribution of the light black ink. For printers like the 3800 which have a light, light black ink (LLK), there are two possible ways to go. One way is to just assign the LLK ink an ink limit of 0 (ie, turn it off as I have done in this profile). The second way is to make the LLK ink also follow the distribution of the LK ink. Either way, the profile will be written for only two Gray Parts. Figure 6, at the end of this manual, shows how inks are distributed in a two Gray Part system. C4

GRAY_INK_1=K

The dark black ink is always the first Gray Part.

GRAY_VAL_1=100

Gray Val 1 is always assigned a value of 100.

GRAY_INK_2=LK C5

GRAY_VAL_2=33

LK is the second Gray Part. I call this the Cross-Over number. It essentially tells

the printer when the LK ink has reached its maximum density and the printer must begin using K ink to obtain darker tones. The Cross-Over number is a constant for a given inkset. To determine it accurately for most alternative processes you need a densitometer that reads UV light. For printers using the older 7 ink Ultrachrome inset the number is

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24. For printers using the newer 8 ink K3 inkset the number is 33. In actual practice it seems that the exact value of this number is not too critical. C6

GRAY_HIGHLIGHT=0

C7

GRAY_SHADOW=0

C8

GRAY_GAMMA=1

Highlight, Shadow, and Gamma are values that can

be used to push the ink distribution curves into rough linearity. I used to spend hours playing with different values before I came to the conclusion they are essentially useless when making digital negatives. I now leave them at their neutral settings of 0,0, and 1. Type a # sign in front of GRAY_CURVE to turn it off. We will return to this Variable later. COPY_CURVE_C=K COPY_CURVE_M=K COPY_CURVE_Y=K

These commands tell each of the other dark inks (C,

M, and Y) to follow the distribution of the K ink. COPY_CURVE_LC=LK COPY_CURVE_LM=LK

These commands tell each of the other light inks

(LC, LM) to follow the distribution of the LK ink. As mentioned above, for printers that use a third gray ink (LLK) you can either turn it off (my preferred option) or tell it to also follow the distribution of the LK ink (ie, assign it some ink limit other than zero, then type in another line of command

COPY_CURVE_LLK=LK).

Now that all the Constants are taken care of, we can go back and set numbers for each of the Variables. V1

LIMIT_K=18 LIMIT_C=18 LIMIT_M=18 LIMIT_Y=18

I set the ink limit for each of the dark inks to the same

number (V1). Higher numbers means more ink on the negative (and a higher contrast

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negative), lower means less ink (and less contrast). A number between 15 and 30 is a good place to start. V2

BOOST_K=25

If BOOST is turned off, all the dark inks follow the same

distribution. If BOOST is turned on and set to a number higher than the other inks, then the K ink will break away from the pack and increase exponentially until, at the very end, it reaches the higher value. In other words, BOOST gives a kick to the K ink in the darkest values of the negative (which control the high values of the print). BOOST increases high value print contrast and makes it easier to achieve pure white in the 0% patch of the step wedge print. There is no fixed rule on how to set BOOST but I often start out by setting it about 50% higher than the limit for the other dark inks. (Even though the C, M, and Y inks are set to follow the distribution of the K ink, they do not follow the BOOST K distribution). V3

LIMIT_LC=30 LIMIT_LM=30 LIMIT_LK=35

This number sets the ink limit for the light inks. I often

start by setting it to about twice the limit for the dark inks. For the sake of simplicity I should have set all the light ink limits to the same number (about 32) but for some reason I did not do so for this profile. Note that LLK ink is set to 0 which turns it off. LLK is a very poor UV absorber, it only contributes to the lightest part of the negative which influences the shadows of the print. I find it just adds to the liquid load on the Pictorico without doing much good otherwise. Make and Evaluate a Step Wedge Test Print. After writing out the above profile, give it a legal name (illegal names will not install), install it, and use it to print out a negative of a grayscale step wedge. Expose this step wedge negative to the emulsion of your choice, develop it, dry it, and take a look. Presumably it will have rich maximum black in the 100% patch (if you established a correct basic exposure). Look at the 0% patch. If it is noticeably gray (rather than white), you need to increase V1 and V2 a bit until you have enough ink density to print as pure white. If several of the lightest patches are pure white, you probably have too much ink being laid down and are clipping the high values. You need

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to decrease V1 and V2. By playing around with V1 and V2 you can often get the light tones to print rather linearly over the range from 0% to 10%. Just keep in mind that the combination of V1 and V2 determines how much ink is laid down in the 0% patch. And the ratio between V1 and V2 determines high tone contrast (whether the tones get darker quickly or more slowly as the % number on the patch increases). Higher BOOST values yield higher contrast in the high tones of the print. Once you have the 0% patch printing as pure white, and a reasonably steady increase in tonal density between 0 and 25%, you can turn your attention to V3 and the light inks. V3 controls the lighter part of the negative (and the darker, shadow part of the step wedge print). If V3 is set too low the step wedge print will become black too fast and there will be no tonal separation over much of the dark tonal range. I tend to increase V3 (lighten the print shadows) until I can see perceptible tonal difference between the 90% and 100% patches on the print. When that is achieved, you can then proceed to derive values for a GRAY CURVE and finish the linearization process.

Making a Gray Curve. If you have adjusted V1, V2, and V3 correctly, you will have a step wedge print in which the 0% patch is pure white and the 5% patch is visibly darker than the 0% patch. Also, you will be able to see a visible difference between the 90 and 100% patches. Place this print on a flat bed scanner and set the scanner to scan in Reflective mode, in grayscale, at a relatively low resolution (180 dpi is OK). Go through the scanner’s control menu and turn off all automatic functions that you can find (you do not want automatic sharpening, dust reduction, or any other automatic adjustment). Prescan the image, find the scanner’s histogram, and set the light and dark sliders so they just include all of the image pixels. Leave the midtone slider at 0. Scan the image and import it to Photoshop. In Photoshop go to Filters>Blur>Gaussian Blur and blur the image so you can barely read the numbers written on each step wedge patch. This evens out the image and makes for more reproducible density readings. Open the Levels window (Adjustments>Levels) and move the white point adjustment slider in until the 0% patch

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just becomes pure white. Likewise, move the black point adjustment slider in until the 100% patch just becomes pure black. Now you are ready to read off numbers and make a table that tells you exactly how far this particular step wedge print diverges from linearity.

Figure 2. Table for deriving numbers for a Gray Curve. You will make two columns for this table. (These two columns are illustrated as the first two columns on the left of Figure 2, above). Label one column INPUT and the other column OUTPUT. INPUT values are the % gray values written on each patch of the step wedge print. OUTPUT values are the actual values you will read from each patch using the Photoshop eyedropper. Click on the Eyedropper tool from the Tool menu, then open the Info palette (Window>Info). In the upper right corner of the Info palette click on the small stack of lines to open palette options and set the First Color Readout to Grayscale. The eyedropper tool will now read K values which for our purposes are the same as % gray. Read off the paired INPUT/OUTPUT values from the step wedge patches and record them in your table. I usually read between 10-16 patches, making more readings from the light tones, only occasional readings in the midtones, and then clustering the readings a bit more in the dark tones. These paired INPUT/OUTPUT values contain the information to create a Gray Curve that will complete the linearization process. But before you can use the paired values, they must undergo several

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transformations. I have illustrated those transformations in Figure 2 using readings from an actual step wedge print. On the left are the two original INPUT/OUTPUT columns read from the step wedge print. Since you are going to apply the gray curve correction to a negative image, these values must be transformed into negative space. Make a new column headed INPUT (neg). Subtract each number in the original INPUT column from 100 and write the result under the new INPUT(neg) heading. Likewise, make a new OUTPUT(neg) heading, subtract each number in the old OUTPUT column from 100, and write the result under the new OUTPUT(neg) heading. Next, you must invert the number pairs. At the bottom of the INPUT(neg) column write OUTPUT and at the bottom of the OUTPUT(neg) column write INPUT. Starting from the bottom of the right hand two columns you now have the proper INPUT/OUTPUT pairs to define a gray curve to finish the linearization process. The INPUT/OUTPUT pairs are typed into the space following GRAY_CURVE= The number pairs must be typed in following strict rules. Immediately after the = sign type a quotation mark (“) followed by the first number pair separated by a semicolon (input;output), then a space, then the second number pair separated by a semicolon and so forth until the final number pair. The first number pair must be 0;0 and the last pair must be 100;100. Type a close quotation mark (“) after the last number. You cannot use more than 16 number pairs. A correctly typed set of gray curve values will look something like this:

Figure 3. Gray Curve number pairs correctly typed into the Gray Curve function of a QTR profile. Be sure and remove the # sign from the front of the Gray Curve line so that Gray Curve is turned on. If all has gone well this final step will result in a profile that creates a negative yielding linear tones in the final print.

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Another Way to Make and Insert a Gray Curve into a QTR Profile. In actuality a Gray Curve is nothing but a Photoshop .acv curve that is inserted into the Textfile to change QTR ink distributions. Rather than type the Gray Curve number pairs directly into the QTR textfile, you can first open the Curves dialog in Photoshop and type the number pairs in there to define a Photoshop .acv curve. Figure 4 shows the Photoshop .acv curve that is defined by the Gray Curve number pairs shown above in Figure 3. To type the numbers in, click on the Pigment Ink % option at the bottom of the window, then click anywhere on the curve line to enter an active point. Then type the INPUT number into the input box and the corresponding OUTPUT number into the output box. Add another active point further up the line, and type in another pair and so forth and so forth.

Figure 4. Photoshop .acv curve defined by a set of Gray Curve number pairs. After creating the Photoshop .acv file, name the file and save it to some convenient place. Then open the QTR textfile, delete all typing following the = sign in GRAY_CURVE=, and drag the icon for your .acv file and drop it right in front of the = sign. The program will enter the address of your .acv file and you are good to go, same as if you had typed in all the numbers into the textfile. For example, this is how the Gray Curve line looks when I drag in a .acv file that is named 3800-Pd.acv, located on my computer desktop:

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GRAY_CURVE=/Users/rreeder/Desktop/3800-Pd.acv NOTE: Only the address of the .acv file is placed in the QTR textfile. If you change the location of the relevant .acv file, QTR will not be able to find it and the profile will either not install or will act as if Gray Curve is turned off. Constructing Gray Curve as a .acv file and then dragging it into a QTR textfile has several advantages. The first advantage is that you get immediate visual feedback concerning how good or bad your Gray Curve may be. Gray Curves should be smooth with no sudden jigs and no part of the curve should ever dip downward and go negative. There is enough error in the flatbed scanning procedure that the first attempt at a Gray Curve is often a bit jagged. It is good practice to manually smooth them before insertion into the textfile. A second advantage is that you now have a fairly user-friendly way to tweak and fine tune the profile. Just grab the Photoshop curve and manually drag it up or down a bit if you think it needs a tweak. Tweaking is illustrated in Figure 5. Manually moving Gray Curve UP on the upper right end of the curve will LIGHTEN high values in the final positive print. Tweaking DOWN will DARKEN the same tones. Same principles apply for the dark print tones.

Figure 5. Effect on POSITIVE PRINT tones of tweaking Gray Curve 18

Figure 6 shows the ink curves that are specified by the final QTR profile, RR3800-UCmK-OHP-Pd. This is the graph that is automatically created when the profile is installed if you type YES following GRAPH_CURVE=

at the top of the

textfile. For the light inks, the symbol “m” shows the distribution of the LC and LM inks. Since they both have the same ink limit, the two curves lie on top of each other. Since, for some peculiar reason, I gave the LK ink a slightly higher ink limit, it shows as a separate line with the symbol “k”. All of the light inks are following the distribution curve of the LK ink, even if they have different ink limits. All of the dark inks have the same ink limit and thus their curves all lie on top of each other, symbolized by “Y”. The exception is the mK ink. Because of the Boost function the mK ink (symbolized by “K”) surges to a higher limit at the far right side of the graph. Note that all seven inks (mK, Y, C, M, LK, LC, and LM) are printing over nearly the entire density range. I think this pattern of ink useage helps fill holes around the dots and promotes smooth image tones. This profile was written as a two Gray Part system. You can see what this means in practice by looking at Figure 6. The dark mK ink constitutes the first Gray Part and all the other dark inks follow its distribution. The LK ink constitutes the second Gray Part and all the other light inks follow its distribution (except for LLK which is turned off).

Figure 6. Ink distribution curves for specified by QTR profile RR3800-UCmK-OHP-Pd

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