Posts Tagged ‘Lightroom’

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How To Color Balance Mixed Lighting Sources

Tuesday, March 5th, 2013

I just finished a series of four blog posts talking about the various advantages and disadvantages of different types of lighting for photo and video work (the first post, with links to the others, is here), and why I’ve decided, for the time being, to use a mixed kit of fluorescent and LED lights. This kit is great and should serve my needs very well, but there is one hurdle that needs to be overcome first: while these lights are all advertised as “full spectrum” and “daylight balanced” at 5600K, in reality they all have visibly different color temperatures, so they need to be balanced with each other in order to work well being used together to light the same scene. In this post, I’m going to give step-by-step instructions on how I took three different lights with radically different white balances and balanced them to work together beautifully.

Before: Unbalanced

Before: Yuck. When white balancing for the mini LED panel on the left, the fluorescent softbox in the center is very green and the LED 1x1 on the right is slightly magenta.

In the image above, which I designed intentionally to exaggerate the color balance differences of the three lights, I placed (from left) a miniature LED panel, a fluorescent softbox and a 1×1 LED panel next to each other and aimed them at a uniformly white ceiling. The difference is striking (and awful).

Before: Yuck

Alternately, the same image above, only this time white balanced for the fluorescent soft box in the center, the LEDs on the sides are both overly magenta and orange.

As is, it would be very difficult to use these lights in a scene together without them appearing different colors. So they need to be balanced together. How to do this? Gels! Pulling out my collection of gels, I got to work.

I keep an assortment of gels to color balance pretty much anything (from left to right): CTOs, CTBs, Plus Greens and Minus Greens each in 1/8th, 1/4 and 1/2 densities. With this assortment, no matter which way a light is off balance, I can balance it.

Gels Gels Gels!

Gels Gels Gels!

In order to balance the three different lights (from three different manufacturers!) I started with the one that is most difficult to gel: the fluorescent (this is one of the biggest weaknesses of fluorescent lights in my opinion… they’re a pain to gel). I used that as my basis and then adjusted the other lights to match it.

It is possible to simply judge the color of a light visually in comparison to others next to it, like in the photos above, and to experiment with different gel combinations to get the lights to the point where they visually look the same to the eye, but “eyeballing” it like that is extremely difficult to do accurately; I have a very good eye for color (I scored a 19 on the X-Rite Online Color Acuity test! Take the test yourself, it’s fun!), and even I can’t achieve the level of precision that I want by eyeballing it. So to measure the color balance precisely I decided to use a couple of precision instruments: my camera and computer.

To start with, I set up a simple 18% neutral gray card on a light stand (I use this one from Amazon… it’s cheap and does the job well), along with a color chart. I lit the gray card and color chart with the fluorescent light (placing the light at an angle so that the light is illuminating the card but not reflecting glare). I then blacked out the windows in my office and shut off all the other light sources (overhead lights, computer monitors, etc.) so there was no “contamination” and I knew all the light hitting the gray card was from the light in question, and I took a still photo of the gray card and color chart with my Canon 5D Mark II camera in RAW format.

Gray Card and Color Chart

Gray card and color chart on stand for determining exact white balance of a particular light

I downloaded the photo onto my computer, and opened the file in Photoshop (you could also use Lightroom or any other application that can work with RAW files, I just happened to choose Photoshop). Using the White Balance Picker / eyedropper tool in the Adobe Camera Raw conversion screen (the same tool is in the Develop tab in Lightroom in the White Balance box), I sampled the 18% neutral gray card to set the proper white balance for the image, the values of which are then displayed in the white balance section on the right (it is a good idea to click a bunch of times in a few places on the gray card as the individual measurements will vary slightly, then average the values).

Sampling White Balance in Adobe Camera Raw

The White Balance Picker tool is the eyedropper icon near the top left. I sampled a spot on the neutral gray card, which gave me the white balance values shown in the white balance box at the top right.

Sure enough, I now saw numerically what I had seen visually on the wall: that fluorescent light was very, very green (+28 tint!). Since that is the light that was most off balance, ideally I would have gelled it to match the other lights, but since this light is so difficult to gel and the other are so much easier, I instead went the other way around and gelled the others to match this one.

With the temperature and tint white balance values for the fluorescent light in hand, I then repeated the process (blacking out the room, lighting the neutral gray card with a single light source, and shooting a photo) for each of my other lights and then found the white balance values for them as well (I found that my miniature panel has white balance values of 5100K temperature and -3 tint, and my 1×1 LED panel is 5050K temperature and +5 tint).

With that information, I then knew precisely how off balance my lights were from each other. I then added a gel to one of the lights, repeated the process of measuring the white balance values, and noted the numerical effect of a particular gel (bear in mind that as much as the gel manufacturers try to keep the color of their gels as pure as possible, a Plus Green gel will never be purely plus green…for example, my Rosco 1/4 Plus Green gels turned out to add +28 points of green tint, but also knocked off 300 degrees of temperature. But after measuring the color balance values of each light and the color effect of each gel, it was very straightforward to figure out which gels to add to each light to balance them together.

In the end, to balance my LED panels to my fluorescent lights, I needed to add 1/4 CTB and 3/8 Plus Green (one 1/4 and one 1/8) to my mini LED, and 1/8 CTB and 1/4 Plus Green to my 1×1 LED, which, while not numerically perfect, got my lights as closely balanced as possible with 1/8th-increment gels. Now I can comfortably use all of my lights in the same scene together and be confident that their colors will be balanced and visually indistinguishable.

After: I've Brought Balance to the Force

After: I've Brought Balance to the Force. While I can still see differences on this uniform white wall, in practical use these lights will never appear unbalanced.

 

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Zaza Gallery Canvas Photo Print Review

Wednesday, July 7th, 2010

So about a month ago (jeez, it’s been a month already…!) I wrote that a company called Zaza Gallery that makes canvas photo prints had offered to give me a free canvas if I would review the product here on the blog. The technology that drives many of today’s photo products is evolving so rapidly that I’m always interested in hearing about and trying out new vendors, so I was happy to take them up on it.

Their initial offer was for a 16″ x 20″ photo canvas. I shoot on Canon cameras, whose sensors are built with a 3:2 aspect-ratio frame (meaning the width of the image is 1.5x the height) and like many pros, whenever possible I use the entire frame when composing my shots (this is a good practice, as it maximizes the sensor area that you’re using for your final composition, thereby maximizing the image quality). As a result, the 16×20 canvas was a different aspect ratio (5:4) than my intended composition. I brought this to the attention of the company, and they generously offered to instead provide me with a 16×24 canvas, which matched my images’ 3:2 aspect ratio.

Zaza directs that for best quality, the image file that customers provide for printing have a resolution of 300 dpi in order to preserve detail in the final print. This is good, because in order to achieve the great detail of true professional-quality prints, high resolution is essential. For a 16×24 print though, this works out to 4800×7200 pixels, or approximately 35 megapixels, which is a higher resolution than even the best pro cameras widely used today (there are a small number of exotic systems that can achieve this resolution natively). What this means is that to make a Zaza canvas print properly, photo-editing software such as Adobe Photoshop or Lightroom is needed to increase the resolution of image files (known as “up-resing”). Since up-resing can result in nasty pixelation, artifacting and other image degradation if not done carefully, images that will be used to print high-quality prints such as canvases must be originally captured in the highest resolution possible.

In any case, for this test canvas, I chose to use one of my more recent photos (featured previously on the blog as the first Photo of the Day, here) which I called “Daybreak”. Here is the photo:

IMG_2562-600x400

I chose to use this photo because it would really put the Zaza printing process through its paces: With its heavily saturated colors it would test Zaza’s ability to color-match, the absolute blacks in the silhouettes and sky would test the ability to achieve true black, and the smooth fade-to-black in the sky would test Zaza’s ability to print smooth gradients.

I prepared the image file according to Zaza’s specifications, with the appropriate resolution, format (Zaza takes standard JPG files) and embedded sRGB color profile (color profiles are essential for accurate color reproduction) and sent the image off. In about a week and a half (which is a normal turnaround time for canvas prints like this) I received the finished canvas. It was packaged well-protected, in a cardboard box in a plastic bag covered in bubble-wrap. Here is the finished canvas:

canvas

Zaza offers a number of different wrapping style options – a traditional “gallery wrap,” in which the image extends beyond the edges of the frame and continues on the sides, white and black wraps, in which image extends only to the edge of the frame and the sides are white or black, and finally “mirror wraps” and “blur wraps,” which are the best of both worlds: the image extends only to the edges of the frame (meaning the image is not cut off), but the edges are colored either by a reflection of the edge of the image or a blur of the edge of the image (which is nice so that the sides, if visible when hung, have some color and look like a real gallery wrap). I elected for the blur-wrap style. I haven’t seen this option with other canvas print vendors, and it is really nice. Your image doesn’t get clipped, but you still get nice coloration on the sides of the frame.

The quality of the final product is very good. The frame is sturdy and the canvas is stretched quite taut and stapled very securely. As far as the print quality:

-The color reproduction is very good. The colors matched the file I provided, and the saturation and vividness are excellent. Neither over- nor under-saturated.

-The blacks are truly black, the white truly white. Overall, contrast is excellent.

-Detail sharpness is average. On extremely close inspection I can make out a bit of fuzziness in the details, but this is to be expected from a file that was up-res’ed. And in any case no one viewing the print on a wall will get close enough to see the level of detail that I was inspecting. No complaints here.

-Like nearly all canvas prints I’ve seen, the print reflects a moderate amount of glare light, so care must be taken in regard to where the canvas is hung to avoid glare light. But again, this is common for canvas prints.

So there you have it, that’s my review! This canvas will hang proudly on my studio wall. Good job Zaza!

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