In search of the perfect eyeball, monitor, camera, printer calibration

My search for perfect color calibration began during a service call from the charter.com folks.  Even thought the signals bars were strong and the cable box had been changed the TV card on this computer was missing channels. Turned out that by some quirk of the transmission, reflection and absorption properties of cable connections, the frequencies of my missing channel were being dragged into kaput-land. Moving heavy furniture and replacing a cable brought them back to life. Turns out cable TV electronic is as quirky and finicky as color management.

During the visit I resurrected my old 32bit machine to avoid running up and down two flights of stairs. It now  has a small flat screen monitor and  I saw that my carefully adjusted image of Matilda (  http://scribble-jpc.blogspot.com/2013/01/tone-mapping-using-ciecam02.html  ) looked too bright.  A trip next door to look on my neighbor's laptop confirmed my big OOPS. What I thought was an accurately calibrated monitor, my Sun workstation 567, was running a half stop too dark

To avoid another big OOPS I set my goals. I would recalibrate using my collection of Sherman Williams paint swatches. (  http://scribble-jpc.blogspot.com/2012/05/how-good-is-my-ancient-sun-workstation.html  )  From http://www.color-swatches.com I would download virtual swatches that came with HSL-- Hue, Saturation and Lightness--and RGB numbers. I would adjust, adjust and adjust until I could lay the real swatch of the paint card against the virtual swatch visible on the monitor and not see a difference. Finally I snap a photo of that comparison with my D7000, display the image, and compare virtual to real again.


That turned out to be a quirky, tricky task. Not surprising since you can buy 500 page books just on the joys and groans of photographic color management.

I  use Sherman Williams paint cards primarily because they supplied color-swatch.com with data for all the paints they sell. Other paint vendors don't. They also print good quality paint cards. Cards from other paint vendors will obviously work but for the record the photo above shows red #82 , green #105, blue #116 and yellow #86. If I was going to repeat this I would switch out the yellow for a card with a wider  range of colors.

My Sun567 monitor has dual color adjustment, the usual brightness and contrast plus gain and bias adjustments for the individual color guns. I won't go into details about that leg of my search since it would be highly specific to a now very rare monitor except to say my attempt to use my D7000 spot meter as a radiometer fell apart because of the Sun's CRT raster scanning. In the end I ran the color gun gains up and adjust the monitor brightness by eyeball. Anyway, if you are using a typical flat screen monitor and not the more expensive professional models you don't have these adjustments. You take what the manufacture gives you.

To photograph and to view the paint swatches  I bought two ecosmart  120 watt equivalent  1100 lumens 5000k daylight flood lamps from Home Depot. I set the white point of Sun567 to 5000k instead of the more normal 6500k to match the lighting. For the D7000 I shot at the neutral jpg setting using a custom WB taken with a 18% grey card.

The  red circle shows the virtual swatch vs the paint chip and measures monitor calibration. The blue circle shows the double  comparison. Both jps's are straight out of the camera without any manipulation and displayed using IRfanview.

I was pleased with the results as long as I ignored the swatches above and to a lesser extent below the matches. These comparisons went bad fast. But there are technical reasons for the problem.

The two swatches that match are titled 'picnic' and 'organic green'.  Their Hue, Saturation  and  Lightness values are  108, 37, 69 and 105, 31, 79.  These values are created by Photoshop in the virtual world and by laying down inks on card stock in the real world. They are fixed.

In the photography world the numbers are not fixed. Since we are dealing with subtractive color Hue Saturation and Lightness are derived from the spectra and intensity of the light being reflected off the paint chips, Something that is far from constant.  And something sensitive to small differences.

How sensitive? If you look closely below the circled areas you can see what looks like a small dirt spec. It isn't. I'm holding the paint card. I can't see any dirt  or change in color.  But  I can feel a slight dimple in the card stock. Since the spotlight is above and slightly in front of the monitor that dimple changed the incident light reflected back into the camera enough to darken the area and cause a hue shift.

The triangle thing in the upper right corner is the sheet of paper I moved about with one hand to attenuate the light as I snapped photos with my other hand. I took more than a few before I managed to adjust the angle of the card, the intensity of light and even where I was sitting in front of the monitor. Taking a good image for this blog wasn't a 'snap and go' task.

Taking a good  'eyeball shot'  was easier. Twisting and bending the card until the colors blended and the seam between the monitor and paint card disappeared. This is also a good time to say that my eyeball matches were always better than my camera matches. The camera may be slightly off. Or maybe it is right on and my eyeballs are off. The CIECAM02 that I've been blogging  is about the quirky way we humans view the world.

I would have ended the post here if I hadn't googled for a bit more info on color management in the middle of writing it.  My Pantone huey calibrator came with a minimum manual, a single sheet, quick start guide. Since the Huey software has on screen instruction and defaulted to 'photo editing and web browsing' I hadn't worried much about the lack until I discovered that Pantone now has a pro version of the software. Its online manual told me I should use the 'Special Warm Medium Contrast' setting to match the 5000K lighting and monitor settings. Not a massive OPPS. All I had to do was change the setting, watch the colors shift and lay my paint card against the monitor. And... not quite a EUREKA moment...but close.

Matching four swatches rather than one or two is a significant improvement. So I won't  talk about how much time I wasted trying to work out a lighting set up so I could match all seven swatches in one photo.

Hitting my goal this close is the good news. Now the bad. My local library branch has a hodge-podge of computers equipped with monitors of different ages and aspect ratios. I checked out all the ones that weren't being used without coming close to matching the paint cards. Worse, one was off so much the lighter swatches were blown out.  The neighborhood center next door has newer monitors and better ambient lighting. My cards still didn't match, but the tonality and contrast looked more reasonable.

So while I have excellent color management on my system. I still publish most of my work on line. With so many uncalibrated monitors out in the world was all this effort worth the trouble? Comment are welcome.

Edit 3/1/13
The original post covered the eyeball, monitor, camera part of the calibration. Now the printer part.
Now and then I do a 4x6 on my old Epson, but the big prints I send out. This one was done at my local supermarket where they combine the best print job in the city with being the least expensive. They keep their Fuji Frontier 570 so well calibrated I see a near perfect color match with RawTherapee's sRGB output profile.

Now it's time to frame the print so it can go up on the wall tomorrow for my camera club's member show. Things are sweet.

How Good is My Ancient Sun Workstation Monitor?

In my last post I mentioned an unexpected  advantage of upgrading my desktop--the discovery that  I now had a video driver specifically for my Sun workstation monitor.  Major result--my monitor colors looked brighter and more vivid.  Minor result--a software switch between my manual screen layout--squished in with black borders so the aspect ratio of  a square image is exact--and the driver's more open layout that fills the whole screen.

I began to wonder if I could go from 'this looks better'  and come up with some tests where I could say 'this is exactly how much better" the colors appeared.  Something like I'd attempted after I bought my first digital camera and wanted to reverse engineer how digital cameras worked. Then I photographed a fan of paint cards and compared the swatches to the colors I saw on my monitor.  With mixed results if I remember correctly.

A decade later I now understand why my naive first attempt at color management ended a bit off.  Somewhere in the house is an extra thick tome on the complexities of  eyeball, brain, camera, scanner, printer, press and monitor color processing.  Someday I might even finish reading it. During my last attempt my brain seized up when I hit the complexities of mating CMYK processing with the ink spread on various paper grades during high speed offset printing.

But I did manage to retain a few key facts. The first is color calibrate your monitor. If that is off everything that follow will be meaningless. To correct gross problems you can fiddle with your monitor controls  and attempt to match images you find on the web. But to calibrate accurately you have to buy hardware.

I invested in a Pantone Huey--at the time $99 at my local we-stock-everything craft store.  The Huey has its quirks.  The software in the box dated from the Win 2000 era and did not install on my newer OS.  Once I located the upgrade, more of a hassle to find than it should have been, I couldn't make the 'adjust the contrast and brightness control so the top right circle... etc etc' part of the setup work. In the end I set them to 75% and clicked next. Despite these quirks, the Huey did cleaned my obvious color management problems. Still I never did discover how accurate the color matches were

So I was thinking of getting out the camera and repeating the paint card experiment when I discovered http://www.color-swatches.com .  Which, not surprising, is a site with a data base of paint swatches. They even provide the RGB numbers used to create the swatch and CMYK numbers to print the color cards. Below is an example of what you find there

So all I had to do was collect some paint card.  Unfortunately finding them in stores I happened to pass while doing grocery shopping didn't work out well. Walmart's ColorPlace wasn't in the data base. Home Depot's Glidden had only one swatch on line that matched the cards I took.  In the end I made a trip to Sherwin Williams. It has a swatch for every paint it sells. This combined with larger than normal paint cards printed on thicker than normal paper stock makes it my recommended store for swiping your cards. 

With cards in hand I download a swatch.  And I hit my first technical problem.  Monitors blasts out light. The paint cards, on the other hand, reflect light. Depending on the light quality (intensity, color temp and all that jazz) they will, more often than not, look different than the monitor swatch.  After holding card by the monitor I could say the swatches sort of looked the same. but that wasn't the accurate one-to-one comparison I wanted.

After some fiddling I discovered if I opened the curtains of a window to the left of monitor and angled the card up or down to catch more or less light I could match the intensities.  But I still ended up with a so-so color match.  Close but hardly perfect like in the photo below.

I must confess to spending far too much time fiddling with controls while the answer to the problem stared me in the face.  Quick question. What is causing the green cast on the swatches of the lighter blue paints?  After all Sherwin Williams wouldn't mix a little green pigment in with its expensive blue paints.

All I had to do was carry the card to the window, twist it first to face the window light and then away, to watch it switch between slightly greenish and pure blue. The Wisconsin clear sky sunlight had started out pure. But once it was reflected off the green leaves that shade the patio below the window it had a greenish component.

Problem solved. Color cast in the light.  Factor that out and the match between real object and monitor image colors becomes almost perfect.  Some days life is good.

Or close to good. Measured with Gimp, the RGB numbers on a swatch are what www.color-swatch.com says they should be.  Measure with RawTherapee using its neutral profile, one that is supposed to display an image exactly as shot, and the numbers end up 5 to 9 units lower  So after I post this I should be a good RT user and also post a bug report.

Edit

The  RGB 5-9 off bug is when I save a swash snip in png format. When saved in jpg format the numbers are off by 1.

And not surprising when you think about it, the green colorcast that had me twirling about mentally yesterday depends on the time of day and where the sun is in the sky.  Around noon when trees are in direct sunlight the reflection off the leaves is a problem.  But earlier this morning when I repeated the test and the sun was much lower in the sky the match was so close I could hardly make out the seam where the card touched the monitor swatch.

Ain't color management tricky ... but fun.