A Study in White and Blue

On a bright and warm May day earlier this week-today is grey and chilly- I went to the Olbrich Gardens to field test new optics. Last Saturday I had bought an oldish Nikkor 50mm f1.8 lens that uses my D7000's internal motor to focus along with a set of extension tubes with all the electrical and mechanical connections needed  to completely control the lens. The hidden artist do-something-different challenge I took on was to leave my zoom lenses in the camera bag and shoot with only the 50 mm lens.

The magnolia trees were in bloom and the sky was blue with wispy clouds. My original shot with RT's neutral profile. Obviously it could use a dose of RT magic.

After a white balance on the magnolia leaves and a default profile.  This version is better but the hidden artist within wanted a bit more ump

The HSV Equalizer tool has been updated  and is now less finicky to use. Dragging its blue bar up or down to change the value or lightness of the blue in the sky seemed appropriate. Here is up. It didn't make a massive amount of difference since the sky's value was already high.

 And here is down which did. Notice how the  blue channel has shifted to the left in the histogram

With the value curve reset I played with the blue saturation curve. Here is up.

And here is down. 

With this image it may not be immediately obvious but a judicious use of both the value and saturation curves is a great way to improve skies without going over the top like I'm doing now. The Hue curve rotates the color wheel to create totally aliens skies. This green version is one of many.

After settling on a moderate increase in the sky's value I went on to the CIECAM02 tool. A large contrast boost of 80 made both the sky and the tree far more dramatic.

And to lighten the clouds  I upped the brightness to 25.

To bring down the blues I played around with the Colorfullness curve.

And as a final comparison here is where I stated once again.

RT's color correction tools are the best around, period. So load up an image the could use a little sky magic and start dragging curves and sliders. I predict you will like what you discover.

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.

Tone Mapping JPGs---Or Why I'm Loving CIECAM02

At times we users fixate on the RAW part of RAWTherapee and fail to notice how great it is postprocessing JPGs. In fact I'd be willing to nominate RT, or should I say JT, as the best JPG editor on the Internet.

Example. I took this image last fall when Wife and I set out on a country ride to find a Halloween pumpkin for the front porch.  At a 'take your pick and please put the money in the cash box' roadside stand Wife walked about selecting the perfect pumpkin while I walked about snapping photos. Like this one of Indian corn.

The corn kernels are especially underexposed. I'd been shooting landscapes with the camera set to -0.33EV so not to blow out the skies and, as often happens, I forgot to change the setting . The camera also picked its exposure based on the bright husks. So how well will CIECAM02  tone mapping with JPGs?

Quite well as it turned out.

For the post proceed jpg I used pretty much the same workflow I described in my last post.
1-click the appropriate boxes to turn on the tools
2-click the highlight exposure warning icon. (white triangle on main tool bar)
3-use a single custom S curve to bring out the colors on the corn cob. When I went too far with the curve, the blown highlight on the individual corn kernels blackened. When I post processed a test jpg using that curve the rich colors washed out.
4-fine tune to taste using the Brighness, Colorfulnes and Contrast sliders

Are the results better or worse using the JPGs instead of NEFs?

 Wife walked in when I had a JPG version up on the screen next to a NEF version. She immediately picked the JPG version as the best. Since I'd used more Contrast on the JPG , I'd lean more towards a tie. With some images using a NEF would be better or even necessary. Recovering blown highlights, for instance, happens before the demosaicing step and won't work with a JPG. But with this image I could pixel peak with tight crops without seeing much difference.

So what are the advantages of using JPGs?

On the technical side speed and memory usage. Users with older 32 bits machines should find this quite useful.

And on the social side, there are mucho more JPGs out in the world than there are RAW files. Even on my machine. I have about five years of JPG only photography from before I owned a RAW enabled camera waiting to be sorted out and made more perfect for the digital version of the family album I've been promising to create.

No more excuses. Just don't tell Wife. Or even worse the Grandmas.

You can find this build of RT at-
http://www.visualbakery.com/RawTherapee/Downloads.aspx

Unfortunately as of January 27 there is no manual entry for CIECAM02. But it will appear shortly. The online manual is at-
https://docs.google.com/document/d/1DHLb_6xNQsEInxiuU8pz1-sWNinnj09bpBUA4_Vl8w8/edit

For Jacques's paper on CIECAM02-
http://jacques.desmis.perso.neuf.fr/RT/ciecamRT3.html

CIECAM02 What IS IT?

If everything goes as planned and everything on the to-do list is checked off the  next stable build, RT 4.1, will be posted in early February. That build promises mucho minor bug fixes, welcome speedups and CIECAM02.

So what is RAWTherapee's latest and greatest addition.  If you google CIECAM02 the wiki entry pops up at the top of the list. If you understand what you read there, email me a translation in people talk. You obviously understand what going on far better than I do. Tis a confusing topic.

In the RAWTherapee implementation we are looking at 12 different sliders coupled with three curve sets and  five curve types. So I will state upfront that if you are looking for a blog about adjusting this slider to create exactly that effect look somewhere else.  I'm not even close to working out those details. But I will say by dragging  sliders around without knowing  exactly what will happen I've corrected many color problems. I've also seen interesting tone mapped HDR images in the developer's forum.  for examples go to http://imgur.com/a/yqzLm#0

With a total of 12 sliders and 5 curves types  CIECAM02 corrects the subtle and not so subtle differences in how we humans see a scene or image and how cameras makes an image. The most obvious difference is chromatic constant or in photographer talk white balance. Another effect, seen by anyone who has thumbed through an optical illusion book, is what wiki calls the white illusion. Both grey patches are identical but they look different when displayed against white or black backgrounds
.

The  'scene condition' section deals with these effects. To quote wiki 'Though the human visual system generally does maintain constant perceived color under different lighting, there are situations where the relative brightness of two different stimuli will appear reversed at different illuminance levels. For example, the bright yellow petals of flowers will appear dark compared to the green leaves in dim light while the opposite is true during the day. This is known as the  Purkinje effect, and arises because the peak sensitivity of the human eye shifts toward the blue end of the spectrum at lower light levels.'

The top slider makes only minor adjustments to the histogram. I check the auto adjustment box in the corner.  With the dark surround--for example viewing a  framed photo hung in a dark hallway-- the change is more pronounced. To counter the Punkinje effect, it shifts the blue channel in the histogram. There are two algorithms for this, the first using only the normal RT adjustments with the second factoring in the CIECAM02 adjustments.

 In the next section there are 9 different sliders if I show them all.

Since I did the screen shots out of order, this is the photo I wanted to create. I started with the shot below, an ISO6400 image deliberately underexposed so I could shoot at 1/125 second when the girls were bowling.

I worked with the brightness and colorfulness algorithm. Instead of colorfulness I could have chosen chroma or saturation. To quote wiki  "colorfulness, chroma, and saturation are related but distinct concepts referring to the perceived intensity of a specific color. Colorfulness is the degree of difference between a color and gray. Chroma is the colorfulness relative to the brightness of another color that appears white under similar viewing conditions. Saturation is the colorfulness of a color relative to its own brightness." Perhaps there are technical advantages to using the other two choices, but I haven't found any yet.

After adjusting for exposure and white balance I did a curves adjustment on colorfulness to create a brightly saturated cake and table cloth along with neutral and slightly subdued skin tones. The dull slider made big changes, the neutral slider didn't do much. With the strong blues and purples in this image the pastel slider shifted the colors more than the saturation slider. When I switched from colorfulness to chroma or saturation the colors shifted slightly. In short with curves and the sliders  I could smoothly adjust the colors to just about anything I wanted. 

Pushing  matters further, with hue slider I could dress the girls in green without destroying the skin tones. 

Finally there is a set of adjustments to correct the differences between viewing an image on a monitor in a well lit room, on TV screen in a darker room or using a projector in a very dark room 

To sum up CIECAM02 is an excellent addition to RAWTherapee