INTRODUCTION
Piezography K7 is intended as a synergistic relationship between seven shades of carbon black ink and a special Piezography curve for the QuadTone RIP (QTR) software. The Piezography designed curve has the uncanny ability to map the entire 8-bit grayscale space (256 gray levels) onto a media. Piezography provided many of these media curves at no charge as part of the installation of (QTR) software. Additional curves are available by purchasing custom profiling services from Piezography. Alternatively, a user can perfect their printer’s linearization by using this premium service.
The 256 gray levels from dMin to dMax are printed using the K7 inks, the K7 curve, and the K7 method of using (QTR). This method does not use the conversion processes often typical of (QTR). Rather an image is previewed with the Gamma 2.2 workspace and printed without any color management.
The reason is simple. Grayscale images exist in 8 bit (256 gray levels) space and Piezography K7 maps this space with a Gamma 2.2 contrast to 8 bit output space. Any color management or conversions prior to printing have a tendency to reduce the amount of gray levels and thereby reducing the fidelity of the output.
Piezography K7 produces its curves with a contrast adjustment of Gamma 2.2 because the majority of displays that can be purchased today are LCD displays that have a native Gamma of approximately 2.2. Anyone who can calibrate their display to Gamma 2.2 can therefore preview their image at the contrast at which a Piezography K7 will print. And if they can preview their image, they can therefore adjust the image to suit their preference. However, it is recommended that the contrast ratio of the display be set to approximate the ratio of ink and paper (about 275%).
Black & white photographers have a very keen eye to tone, and most wish to preview the image exactly as it will print. This requires correctly calibrating the display for print which is uniquely different than calibrating for photography, or calibrating for animation. A display that has been calibrated for print is reduced in output illumination to imitate the effect of ink on paper. This imitation allows the photographer to see the approximate level of black and white with the correct gray ramp between them. Another benefit of proper calibration is the ability to use a soft proof ICC profile with extreme accuracy.
While Piezography K7 can be used without calibration, its potential for the photographer can be furthered through a calibration process that allows the photographer to match the display image to the print in a manner that includes not only the correct dynamic range, but also the color of the paper and its influence on the color of the inks. This is part of the Soft Proof ICC profile process used in Photoshops custom Proof Setup. While we provide Soft Proof ICCs in Special Edition for the 1400, customers can make their own provided they have a measuring tool such as the EyeOne.
STANDARD VIEWING CONDITIONS
The first step to Soft Proofing is setting up the conditions and environment under which the photographer will simultaneously view the display and the print. This environment will allow the photographer to judge whether they have a good calibration and soft proof. If the photographer does not wish to use ICC profiles for soft proofing, this step can be skipped, although I recommend the practice of standardizing the environment for anyone using calibration or soft proofing.
Both the D50 and D65 standards expect a viewing condition in which the monitor is calibrated. Typically the room should be no brighter than 50 lux which is perhaps just a little brighter than the illumination from the display and a viewing booth located adjacent to the display. The room should not be painted in bright colors, nor should the viewer be wearing brightly colored clothing so that neither will reflect onto the display thus influencing the perception of the viewer. All light in the room including the display, the viewing booth, and any additional lights which cast their illumination on either the print or the display, must be of the same color temperature as the standard (D50 or D65). If a viewing booth is used, the booth must be of the type that can be dimmed to the brightness of the display.
Choosing which standard to calibrate to is up to the photographer. The reason that D50 is the standard for professional printers is because of the physical attributes of human perception, rather than any industry commercial pressure or interests. A scientific study in 1931 by the CIE concluded that the average human being saw equal amounts of red, green and blue light at a color temperature of approximately 5000 Kelvin. Under this color of light, the average human could best perceive the differences and similarities in two adjacent colors. The CIE also adapted a methodology of describing color through measurements called CIE Lab color. The basis of this study formed the core of ICC color management. The D50 standard is very well supported with paints for walls, light boxes for viewing, and light bulbs. As an example for those coming to train at Cone Editions Press Workshops, the entire building is illuminated with 5000k fluorescent lights. Color can be judged in any part of the three story building whether in a proofing room or in the community lunch room.
The D65 standard uses 6500k which is equivalent approximately to daylight in the Northern Hemisphere. Many imaging gurus have cited that they prefer the color of 6500k over 5000k. But color management is not about preferences. It is about human perception and the ability to judge color. The more compelling reason to choose D65 is because the common LCD which has little or no control to adjust its hardware is illuminated internally by a fluorescent source at about 6500k. D65 is not well supported in the industry. By example, there are few D65 viewing booths available.
Under no circumstances should the photographer follow the advice of anyone who states that it is best to calibrate a display to 6500k and compare the results to a print in a 5000k viewing booth. This advice ignores the complication presented by the human perception system that can not simultaneously adapt to two different white points. If a human being looks at two examples of the exact same color under 5000k and 6500k simultaneously, the human will perceive two different colors rather than the same. With a neutral gray by example, examined under 5000k and 6500k, the gray will appear cooler to the human in the 6500k when its compared simultaneously to neutral gray under a 5000k light. But, if a human only sees one light source, the human will adapt so that a neutral gray will appear neutral under 6500k or will appear neutral under 5000k, just as long as no other white point illuminates the color example.
The most important part of this step is creating a viewing area with one type of light. If the photographer is using a CRT or an LCD with an onboard 12-16 bit processor, I recommend the D50 standard. If the photographer has an ordinary LCD, I am afraid if they do not calibrate to D65 they will not be able to display 256 gray levels on the display, and that is more important potentially than the best possible soft proofing. The reason that they may not be able to display 265 gray levels is because with the exception of hardware calibrator reference displays, calibration is performed using software that adjusts the video board of a computer. To change the color temperature of a 6500k LCD to imitate 5000k requires considerably limiting the output of the video board on two of the three channels. Since any limiting to the video out reduces it from 265 gray levels, a display of this type should be left to its native white point.
Note that 8 bit RGB color is 265red x 265green x 265blue = 16.7 million colors. Certainly, no photographer will notice a few hundred thousand colors missing from a display of 16.7 million. However, accurate grayscale depiction requires very close to 16.7 million colors in order to produce 256 combinations that appear as gray, or banding occurs and the ability to differentiate 256 gray levels is sharply reduced. And the truth about accurate ICC soft proofing whether for grayscale of color images is that the display needs to be calibrated very accurately. This is the main reason why calibrator reference displays are so desirable.
DISPLAY TYPES
Note that a calibrator reference display and an ordinary display differ because calibration in the former is performed directly on the display, whereas calibration on the latter is performed on the video board. The calibrator display sometimes referred to as a reference monitor or a hardware calibrator display is unique in that it utilizes an additional input cable that runs adjacent to the output video cable. This input cable is used to adjust the display during calibration. The instrument which is used to measure color is exactly the same type of instrument used in calibrating the video board. But the feedback from the instrument is looped through a special calibration software that makes adjustments to the display. These displays have billions of possible color combinations. When the calibration is complete, the video board of the computer is left untouched and outputs 256 levels of gray for each of the rgb channels.
Examples of these displays as CRTs are the very excellent and discontinued Sony Artisan, and Barco Calibrator, and honorable mention to the LaCie Blue Hood with Blue Eye. Examples of these as LCDs are the very excellent Eizo CG series, and the NEC Spectraview II series. All of these displays share in common a (DDC/CI) circuit which with an attached USB cable allows software access to the display hardware which has considerably more available colors than the computer’s video board. Do not confuse this port with the USB ports available on most LCDs. With a calibrator display, the process is literally automatic and push button. The photographer chooses a white point (color temperature) and Gamma and usually is able to specify a brightness range suitable for either print or photo (they want print for soft proofing.) With advanced features the control over the brightness range can be set to perfectly imitate ink on paper.
The best bargain for a calibrator display is the Eizo CG222W available from InkjetMall for only $1,399
The makers of calibration products for ordinary displays advertise that they are automatic and virtually push button. Yes they are. But no they are not. The average consumer can considerably improve their display by automatic calibration. However, the photographer who is expecting a near exact match will need to use the advanced features and some manual intervention if they have a hope and a prayer of arriving at a calibrated state with a video board at or near its full output of gray levels.
An example would be automating the calibration of an ordinary LCD to 5000k. The result will necessarily be a video out reduced to as low as 180 levels in one or more channels. Brightness may also be reduced on the LCD by reducing it at the video board. These calibration products can be used however in an advanced mode in which the photographer is expected to manually adjust the display using the controls of the display (if they are available) to tune the display to the desired target using a feedback portion of the calibration software. The instructions for this are beyond the scope of this paper.
Note that most CRTs have a panel of adjustment buttons which can be used to change the brightness as well as the color temperature. Often the presets which accompany these adjustments are considerably off. Pure manual controls allow the calibration software to give feedback. While this is not as accurate as using a reference calibrator display, it is of the same concept. So it is worth spending this type of time to hit the targets of brightness, color temperature, and the black point (associated often with brightness) using the manual controls if the calibration software package allows it. Then the calibration needs only make small fine tune adjustments and a linearization according to the desired Gamma. The end result should be superior to simply clicking on the automatic option.
Note that many LCDs do not have any controls to adjust color temperature. Some only allow adjustment of brightness. Several however are available which give the photographer access to a larger bit space of color internal to the display. With these controls, the photographer can reach the targets of the color temperature and brightness using the advanced features of calibration software packages. Remember the less work that the software does, the more intact the video board remains.
CALIBRATION OF DISPLAY FOR PRINT
If you have a calibrator reference display, the software that accompanies it allows the photographer to choose several options during the calibration process. Some of the video board calibration products also have several options which the photographer can choose. The scope of all of these products is beyond this paper. However, a description of the desired finished state of the display may be useful in understanding the options that are presented by the various packages.
Calibration to print results purposely in a very reduced dynamic range of brightness on the display. The reason is purely simple. If the display is going to be used to judge color on printed media, then the display needs to assimilate as closely as possible the dynamic range of the printed media. By example, a display can possibly have a dynamic range as high as 4.0 from white to black while a print is often of a lower dynamic range averaging about 1.8. Piezography K7 on Photo Rag can be as high as 1.65 (dependent upon paper batch) and as low as 1.45 on other sheets. Piezography MPS Glossy can be as high as 2.1 on some media. For there to be a similarity between what is perceived on the monitor and the finished print – the dynamic range of the display must necessarily be reduced.
A typical display after automatic calibration can produce a black as low as 0 and a white often much higher than 100. Piezography K7 on PhotoRag averages about 16.2 for black and about 97 for white. The goal therefore is to choose settings during calibration that reduce the brightness levels to approximately this ratio. It can be slightly larger, but not significantly larger. Slightly is 14 – 98. Significantly larger is 0 – 100. Calibrating for photo display produces a much larger dynamic range than calibrating a display for print. Do not be confused by an option for “photo”. Unfortunately, the makers of LCDs realize that more people view DVDs on LCDs than attempt to soft proof an ICC profile, or use it to preview grayscale images intended for print. As such, it is probable to have an uncalibrated LCD with a contrast ratio exceeding 500.
The average photographer versed in some technical background concerning color management would realize that a display which is bright enough to view DVD from 30 feet is probably too bright to preview an image destined for print. However, the brightness ratio between black and white really should be calibrated to a very narrow range. My “slightly larger” numbers are generous if very accurate previewing is desirable.
If your neighbor who purchased an LCD about the same time as you did, comes over to see how you are getting along with yours, and comments it looks terrible compared to theirs, then you probably have succeeded in calibrating your display to print. In a side by side with an un-calibrated LCD, a calibrated to print LCD will look very muted and very dull. It will look more like a sheet of paper with light reflecting off it than a backlit dazzling display screen perfect for looking at websites and DVDs and pics of the last vacation. The goal is to create a correlation in display and output which the human perception system can readily adapt to.
Note that a display calibrated for print should not be used to make final adjustments for web images. It does not go without saying, that a photographer might have several calibrations that they use. I can tell you that I use my display often for making images for the internet. I do not presume that everyone on the internet is looking through a display calibrated to print. Rather, I assume most people are on Gamma 2.2 LCDs in sRGB space. So I have multiple calibration settings on my Sony Artisan which I can switch on the fly in less than 15 seconds. I recommend that a photographer explore multiple calibrations including one for viewing DVD movies! Why not? I love LCDs for movies. I like them less for critical color management. But I insist on perfecting as closely as possible the calibration for print.
NOW WHAT?
At this point you have spent some considerable time reacquainting yourself with either your calibration software or our your hardware calibrator display. Your calibration is perfected or is at the least considered to be perfected. Lets test it. The best test is to bring up a grayscale image in Photoshop. But first lets set up Photoshop’s Color Settings to reflect the needs of Piezography K7.
Because Piezography K7 only requires a single channel 8 bit grayscale image, the photographer can make use of the Grayscale settings in Photoshop Color Settings. Here is where the grayscale workspace of Gamma 2.2 should be preset. Because Piezography K7 prints a Gamma 2.2 linearized output, the photographer should set some rule preference to how images are handled that are not already in Gamma 2.2. It is possible to simply select the convert option, but I prefer to be notified so that I have the option of knowing that an image is in another workspace preview. So I choose the ask when opening options.
When a Gamma is attached to an image during saving, it serves as a preview for the next time it is opened. Lets say that you have several hard disks full of images which you previously printed with PiezographyBW ICC. PiezographyBW ICC printed with a Gamma of 1.8 because it was D50 compliant. If the display was properly calibrated the image would have previewed as it printed with that system. However, if the display is properly calibrated to Gamma 2.2 and this older legacy image in opened in Photoshop, the Color Settings rule governs how it is treated.
I prefer to choose the option when I encounter this situation because rather than automatically converting the image into Gamma 2.2, I want to look at it in Gamma 2.2. Perhaps, I will not need to convert it, or perhaps I may only need to slightly adjust it. This is a preference that the photographer can decide for themselves. However, the correct Piezography K7 workflow is to print images that are in the Gamma 2.2 workspace. Assigning or converting that workspace is your preference, with the understanding that the Gamma conversion is a slight modification to the pixels.
Once the image is opened in Photoshop and the Gamma 2.2 is assigned, the photographer should make a print as follows. From Macintosh, the Print command is selected; the Quad-K7 printer chosen; and the option in the Print window selected to QuadTone RIP. In the QuadTone RIP interface the correct media curve is chosen; the dpi is set to 2880 and the quality to unidirectional. No other adjustments or settings are made.
Windows users can open (QTR) interface in parallel to Photoshop. The image is opened in (QTR) and printed using the same settings above.
Once the print is finished it can be dried down to its finished state by using a hair dryer for 3-4 minutes. The print is placed into the viewing booth adjacent to the display. The viewing booth is then dimmed to approximately the same illumination level as the display. While dimming, the photographer will observe the phenomena of the contrast of the print changing. It will become self-evident why a dimming viewing booth is specified in the D50 / D65 standards. It is a critical piece of the equation!
If the display is correctly calibrated, the photographer will observe that the contrast ratio between print and display is very close. If the display is close enough to permit confident image editing, then the photographer can proceed.
The option of using Soft Proofing will perfect the contrast ration, change the white to that of the color of the profiled paper, and adjust the black point of the monitor to appear as if it is ink on paper (a reflective black.) The creation of Soft Proof ICCs is documented in (QTR) and is part of the download.>
In Photoshop’s Proof Setup / Custom the ICC created in QTR for previewing is selected. The preserve numbers, display options, and preview box are checked. The image on screen, if it changes abruptly in contrast signals that the calibration to print is off. If the brightness of the image is reduced significantly by the soft proof, then the calibration is too bright. It is a very good indicator of the calibration process that was undertaken earlier.
A good soft proof only changes the color. That is the goal. It is easily obtainable by using a calibrator reference display. It is achievable also with a software calibrated display if you reduce the load on the video board by making as many of the adjustments required to your display (if possible.) Sometimes, the part of calibration which is most sensitive to ICC soft proof is brightness. It controls the darkest part of the display as well. Find out what you can do in your software package to calibrate to a dynamic range which is similar to print.
AFTER THOUGHTS
A few things to point out. There is absolutely no gain to converting an 8 bit image into 16 bits as far as Piezography K7 is concerned, because the conversion does not increase the gray level from 256 to 64,000. The 256 levels remain and no amount of adjusting will increase these levels. The human eye can detect the changes in gray from 0 to 255 but not all simultaneously. The human perception system can only differentiate about 125 grays at one time (in one focus of perception). But, the focus can shift across the grayscale and the brain detects the differences in another range of tone.
16 bit grayscale likewise, can not be printed with seven inks and the dithering possibilities. It is extremely overkill and mathematically does not produce a gain when printed. However, if an image can be captured in 16 bit, it will have 64,000 gray levels, and can be edited in a much less destructive way. When it is converted to 8 bit prior to printing, the most appropriate 256 gray levels are chosen.
Likewise, there is no gain to keeping a grayscale in RGB mode, or converting from grayscale to RGB mode.
To help you judge the match between display and print, you should try and imitate the print on your monitor. If you printed with a margin, you can temporarily put a white canvas around your image during soft proofing. Otherwise, the brain sees a gray against the monitor background which might be gray itself, or black and it can not judge whether it is the same gray as on the print. Keep the comparison areas around the image congruent by trying to equalize the conditions in both the booth and monitor. Now you can make a judgment call.
Look at the two carefully and determine how close the match is. Remember that if the soft proof dramatically changed the display, its still too bright.
The goal is that what you see on the monitor looks like what is printing. If it is, you can now edit the monitor image to suit your preference for contrast and print with confidence. You are also getting all of the 256 possible gray levels.
None of this is particularly news. But I often forget how many new users come into Piezography and are also new to calibration, etc. I’ve been doing this for so long that I often forget how difficult all of it really is until one is used to it.
And therefore I will close with the fact that only pixel values of 0 will print as black. Only pixel values of 255 will print as white. What you do with the other 254 gray levels is totally up to you.