cgardner
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 Re: Microprinting surprise on test print | |
skid00skid00 wrote:
cgardner wrote:
When output resolution is set in Photoshop at say 300 ppi, that indicates how many pixels in EACH COLOR will be printed per inch. Printer makers express resolution in terms of total dots of all colors. So 300ppi in Photoshop x 8 colors becomes 2400 \"dpi\" on the printer.
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I disagree. Each \'color pixel\' will index to the same spot on paper. A yellow pixel overlays a green one. Epson\'s diffusion might blur the edges of each color pixel. The Epson R1800 printer indexes 5760 x 1440 dpi at it\'s highest resolution. The images ppi setting in the image file doesn\'t control the ink droplet spray pattern, the Print Quality setting in the printer driver does.
My example was just a gross simplification not a detailed explanation of the process. For example, Epson printers have heads with 360 jets per inch. That\'s a very real physical design factor. But those 360 jets can be driven in a variety of ways with software with frequency modulation of ink spray vs printhead and paper movement and droplet size to alter the way the ink is deposited. These physics of color separation also dictate that the inks must be transparent and in the correct but unequal proportions of CYM to create neutral colors because unlike RGB light the CYM inks aren\'t pure. Cyan is cross contaminated with Magenta and Magenta with Cyan.
Color printing technology has come a long way in a short period of time. I\'m only 57 but as a kid growing up in the 1950s and early 1960s my windows on the world were LIFE and National Geographic magazines and grain B&W photographs in the letterpress newspaper. My point of view on color comes from a longer and broader perspective of doing color reproduction with analog methods and far less sophisticated equipment than most here have. Over the years the equipment has become more sophisticated and difficult to understand, but the physics of color and human perception have remained the same. The goal of the exercise is also still the same: tricking the brain of a viewer into thinking an image in a photograph is something three dimensional and real WHEN VIEWED NORMALLY. There\'s no single set of criteria for \"normal\" because human perception is based on context and what the memory of objects expects us to see. We perceive a white shirt to be white in any light because we expect it to be white.
Back in college in the early 1970s when I first got the photographic bug I taught myself the Zone System and became an art major not because of any artistic temperament or talent but as a way to get credit for what I enjoyed doing most, photography. The Zone System taught me about the relationship between what the eyes see and how a photograph must be manipulated to create the illusion of reality. I made my first halftone in 1972 as the black printer for a photo silk screen.
I quit college to pursue photography - photojournalism - and wound up working for Monte Zucker shooting weddings for two years. That was interesting and educational but not what I wanted to do for the rest of my life so I jumped at the opportunity to work in the photo labs at National Geographic when I learned of an opening there from a neighbor. The fact that he was asst. chief of the lab was a stroke of luck but it teaching myself to make a decent B&W zone system print and also how to make a halftone is what got me the job and started me down the road to a career in printing.
At National Geographic I did halftones and color separations on a process camera with 133 and 150 DPI contact screens. I also used one of the very first DuPont Cromalin pre-press proofing systems. I first learned of the concept of color management and 3D colorspace from the color scientist at DuPont who invented the Cromlin system over lunch during a field trip to DuPont. He used a lucite cube with pins representing the most saturated colors in CYMK ink and the Cromalin pigments connected with colored yarn to illustrate that colorspace is three dimensional. Today I can compare gamuts with 3D wireframes using the ColorSync utility in OSX...
... and understand what it represents thanks to the education I received years ago. By 1980 I\'d taught reproduction at the college level for five years and advanced in printing management to production process manager at a large web printer of mass circulation magazines. As you work your way from act of capturing a photograph to reproducing in on a high speed press the number of variables and mechanical limitations affecting the outcome increase. The science of color management evolved to make the changes to the image predictable, not to match all the devices, something which is physically impossible in most cases.
In the mid 1980s I was production manager of the US Information Agency printing center in Manila, Philippines where we printed color magazines and books which were distributed around the world by Public Affairs sections at Embassies. The operation ran and still runs like a self-sustaining commercial publishing operation: we only print what the market demands and that has changed over time. In the 1980s color was separated from transparencies, 35mm originals or duplicates of 35mm on 4 x 5 or 8 x 10 Ektachrome. We had some of the first scanners produced by RCA in the 1970s and were already using the second generation Hell DC300 when I arrived in Manila in 1983. Back then I knew the % of YMCK needed on every step of a gray scale to achieve neutral gray balance. That was necessary because getting simple gray balance in a separation - separating a gray scale and having it appear gray in the reproduction - wasn\'t automatic and took a good bit of expertise and time twiddling knobs, and repeated test runs to achieve. Today we can attach a hockey puck to the screen and click a button and be blissfully ignorant of how color is being adjusted. Its convenient, but sooner or later ignorance always bites you in the backside in the form of results you can\'t explain because the underlying cause and effect isn\'t fully understood.
As a result of my analog experience and everything learned prior to the arrival of digital reproduction I have historical perspective of how software and equipment evolved. In most cases physical limitation in equipment dictated design factors and in other cases the limits of human perception and how the brain is fooled. The first images where produced on dot matrix printers with a physical limit to how many pins could dance on a single halftone dot. Inkjets have similar physical limits of nozzles per inch but more sophisticated ways to control the ink sprayed from them have evolved to the point the knowledge exactly how they work buried in the driver code and known only by a very select few who design the printers and write the code and others who make their living as color management experts.
Back around 2000 ICC based color management was the Holy Grail in professional graphics which was touted as solving a range of color workflow problems. It can in a working environment where all the variables can be controlled and devices precisely by skilled operators using expensive equipment. But ICC based color management is based on the fact that absent direct comparison of two different gamuts the brain will adapt to either as the baseline of \"normal\" color if memory reference colors are correct and gray balance is maintained...
Here is the same RAW file of a MacBeth color chart rendered with four different styles in DPP:
None of them reproduce the color accurately but they all have reasonably accurate gray values with the color management in styles kept consistent. Which is the best choice of color? That would depend on the content and desired impression the color balance was intended to evoke. What to do in that situation? Try them all and see which best meets the goals for that photograph. Its a moving target which changes with every photo.
I\'ve seen digital color management evolve since the days when an Apple color monitor adjusted visually with Adobe Gamma was the only de facto standard, and as a result I have a great appreciation and respect for the engineers and color scientists who have made color printing no-brainer easy today with ICC based color. The $120 8/C HP printer on my desk produces results which blow away the prints on my wall I produced 10 years ago with a $25,000 dye-sub printer. Because I realize at this point in time the people designing the equipment know far more than I about managing color, and I\'m not equipped with the tools to do it any better, when I send files to the printer I let the printer manage the colors.
I control my color workflow in the camera, which is how I generate it. What better baseline could there be? I use custom WB whenever possible and batch correcting off of known neutrals in images when I can\'t.
Starting from that \"neutral by the numbers\" baseline from the camera I don\'t need to be anal retentive about monitor calibration. I don\'t even own an automated calibration device because I know after opening and looking at an image I know to be neutral my eyes will adapt my perception to make it neutral. Because it is known to be neutral \"by the numbers\" as verified by the eye dropper values on the gray card or any other known neutral object I know it will look \"normal\" with correct gray balance on anyone\'s monitor, even an unbalanced one if they expect the card to look gray. That\'s how magicians fool the audience; by understanding how to fool the brain.
Assuming the photo has correct gray balance the color saturation will fall wherever the gamut of the camera, working space, and monitor put it. What I see and make perceptual judgements based on is the monitor gamut, which is slightly larger than sRGB on my iMac...
... and Apples and Oranges compared to the gamut of the printer on my desk....
What I see on my monitor is actually much closer to what the printer down the road at Costco produces....
I know that I take that file which has perfect gray balance and a full range of tone out of the camera by the numbers and start screwing around with it based on what I see on the screen the process is akin to brain surgery by remote control. Because I\'m only seeing the color the screen gamut can display and its is much different in size and shape than the gamut of the printer any diddling with the color to try to make it more saturated is like shooting fish in a barrel blindfolded. More often than not when shooting blind you hit your foot with the bullet instead of the target.
I deal with the fact my prints don\'t match my monitor in a very practical way: I ignore it and don\'t compare them side-by-side. Its a pointless exercise. The goal of color management is maxing out the gamut of each output device. What to know what your printer gamut is capable of when reproducing saturated primary and secondary colors? Make a test file like this in photoshop in ProPhoto RGB working space and send it to your printer letting it manage the color...
Then compare the colors in that test print with the colors in your images from the same printer by punching holes in the test print and putting them over your image prints. If for example the photo is of a red card and the red in the card is as saturated as the red patch in the gamut test it will tell you its as red as the printer can make it. Just don\'\'t compare the print to the image on the monitor or the car itself and the car in the print will look just as real.
The optimal way to handle color management is to keep the image in RGB in a wide gamut and let the printer manage the color. That approach works quite well when the printer driver has a profile for the paper and ink being used. Things go off the tracks when the \"canned\" profiles don\'t match the paper and ink. Paper and ink vary so the profiles will never be 100% accurate. Targets can be printed and custom profiled generated, but it is a time consuming process and expensive even if done in house. High-end ink jets now have the ability to create their own custom profiles \"on the fly\" with built-in colorimeters from whatever paper is being used. Sooner or later that same technology will trickle down to less expensive printers. Until then the best way to manage color on desktop printers is to use printer brand papers formulated to work with the inks and profiles stored in the printer and let the printer manage the color.
Beyond printing variables making objects in prints look real starts with anticipating the effect of printing variables at the time the image is capture in the camera. It is a given printing causes a loss in contrast perceptually and dot gain causes a loss of shadow detail vs what is seen on screen, so if you don\'t start with good contrast in the lighting and a full range of tone at capture you start with two strikes color management and printer resolution can\'t erase. Being an old zone system practitioner I am anal retentive about recording detail everywhere in the tonal range at capture. In a studio setting that\'s easy no matter what DR the camera has. First for the shadow detail to lift it to where the camera can record it..
then overlap all the other lights, keeping the brightest under clipping except where specular highlights are needed for the illusion of 3D, then balancing all the others by eye perceptually so the balance looks natural and real.
Realism in photographs comes from mimicking the direction of natural light - our perceptual baseline for normal lighting patterns -- and using contrast clues to trick the eye into thinking objects are real and 3D.
Outdoors we have the technical dilemma of a scene with 10-12 stops of detail and a camera with a 6-8 stop recording range. But there are strategies which can overcome that problem.. One is to use relatively flat light and make recognizable objects large in the photo...
Ambient only, direct sun..
Parts of the scene exceed the range of the sensor but the really important stuff we recognize is exposed to look as normally perceived by eye..
Same light, objects and exposure for detail in the highlights, shot from the opposite direction:
All the technical variables are the same but the angle of the light creates more contrast and changing the size of the target relative to the background and putting the target mostly in shadow changes the context of the target in the scene. The shade parts of the card in the first shot above are about the same, but they aren\'t really noticed because most of the photo looks \"normal\". In the second shot the towel is correctly exposed with detail but the rest of the photo looks underexposed. That\'s how our brains are fooled and the difference between technically correct exposure for the highlights and what looks normal perceptually.
Expose the ambient highlights below clipping, shoot into the shadow with flash with no overlap and the foreground can be raise to look \"normal\". The background is still darker than normal making the target seem overexposed a bit. But if you were to crop in progressively and change the perceptual balance of foreground and background the tighter the crop the more perfectly exposed the target (or face in the same place) will appear...
Technically perfect exposure and what is perceived to be perfect will coincide when the balance is right. This was shot using the same technique with one flash....
What looks right can only be determined subjectively by eye. The goal is to attract the viewer to what is most important in the photo and hold attention there so it will create some form of emotional reaction. If it doesn\'t the photo isn\'t very effective. Contrast plays an important role on many different levels and perceptually is far more important than fine detail in a photo...
These tangents might not seem to relate at all to the topic of printing, but it has a lot to do with how reproduced images are perceived at various distances. As the viewing distance increases starting with an image containing strong contrasting elements defining shape will result in a more \"real\" looking image. Up close detail drives perception because our eyes only really focus on the center 2 degrees of our FOV. So if you are looking at a 8x10 print or still reading this your perceptual universe is only really this wide >>>>>>><<<<<<<<<<< twice the width of your thumb at arm\'s length. Your brain tunes everything else out.
But when you look a photo from across the room your brain is influenced more by everything in the field of view competing for attention...
... and a photo which is compelling because of a pattern of detail becomes less a less compelling sea of sameness when viewed from further away. A perceptual trick which can used when displaying photos, borrowed from interior decorating, is to display objects in groups of three and use the those with with more eye catching detail from a distance to frame the ones with detail and invite closer inspection. Seeing past the narrow confines of the single photo to find a way to make it work holistically in the space it is displayed.
There are a huge number of variables affecting human perception. Changing the viewing distance or the intensity and color of the light in which the image is viewed are just a few of the more important ones where having more dots or ink blot per inch doesn\'t result in the best looking image perceptually. Its something painters realized and incorporated into their painting techniques. Visit an art gallery with original paintings by John Sargent Singer and you will get a master class on using contrast to create the illusion of sharpness. Singer produced larger than life portraits which when viewed from across the room seem to have razor sharp detail. But when you walk up to reading distance 18\" from the canvas you will discover he literally troweled on the paint with a palette knife and the illusion of sharpness comes from the contrast of playing the specular highlights create on the raised areas with dabs of white paint with the darker areas those raised areas would cast in natural light from above.
All of photography is an optical illusion which tricks the brain. Understand how that process works and you\'ll better understand how to make images which appear more natural and real in a photograph. It starts by lighting them in a way that creates contrast patterns which translate into the same patterns see and stored by eye. The stronger the contrast in the pattern, the greater the illusion of 3D shape. That\'s why an image with well defined contrast holds up better and looks more real as it is reproduced larger and seen from further aways. Posterization and pixelization, while objectionable in an image viewed at 18\" are the the things which make an image viewed from greater distances, beyond the resolving power of the eye, look sharper PERCEPTUALLY.
Chuck
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