White balance for digital capture is actually similar to days of film in some regards. Especially relevant when dealing with tungsten lighting when shooting stills or video. Why?
Because tungsten lighting is a dynamic-range killer due to it being deficient in the blue channel. Using custom white balance in-camera doesn’t solve the lack of blue light. The amplification in the blue channel raises the noise floor. Its bad enough that the blue channel is the weakest on many sensors, but ramping up that channel often worsens the noise even at relatively low ISO levels and goes downhill quickly as you raise ISO (which amplifies all channels). Solution? 80 series filters.
The 80 series filters were of course for color conversion when shooting daylight color films in tungsten lighting. The 80 series vary, but I”ve found the three most relevant to be the 80-A, 80-B and 80-C, each varying slightly (chart provided later in the post). The result of using an 80A for example is that you suppress everything but blue light. This is what you get when you use a digital camera set to daylight white balance with an 80-A filter in front of it ==>
The following is happening:
— Red, green and blue levels in the light source are approximately equal, and tungsten light looks white. Subjects in that light look normal.
— Blue channel noise is reduced even at high ISO settings because the blue channel is being “fed” per se. Dark shadow noise is reduced tremendously.
— Red-channel overexposure halos (also known as “blooming”) that occurs around edges of light sources, is reduced.
— (THE DOWNSIDE) Exposure time is increased by 2 stops for an 80-A (so 1/250 sec ends up being 1/60 sec, or 400 ISO becomes 100 ISO). It is best to use color-blind centerweighted metering.
| 80 Series Filters Color conversion (blue filters) |
| 3200 K to 5500 K |
80A |
Loss of stops = |
2 |
| 3400 K to 5500 K |
80B |
Loss of stops = |
1 2/3 |
| 3800 K to 5500 K |
80C |
Loss of stops = |
1 |
Again, tungsten light is a dynamic-range killer, and using your camera’s custom white balance abilities can’t fight it alone. If you value using every ounce of the dynamic range of your sensor, it is important to make adjustments to light temperatures BEFORE the light hits the sensor. Dynamic range is measured from the noise floor, which is affected by blue-channel noise. Using a blue filter in tungsten lighting will help allow your camera’s sensitivity perform as well as it does in daylight color white balance where channels are more even (RGB).
In real estate photography this becomes extremely common and relevant where the goal is to find ways to INCREASE dynamic range. You certainly don’t want to make your life more difficult by relying solely on a camera’s custom white balance. And if you are bracketing for HDR and you are concerned about noise???… well this is just as relevant. Because most shots are taken from a tri-pod, the loss of stops using an 80-A 80-B or 80-C filter are less dramatic then if you hand hold shots.
The 72 dpi myth was something that had me scratching my head years ago. I was wanting to use some high end compositing packages to edit photos, but I was concerned about the fact that they deal in video “speak” and 72dpi was/is the norm. So I was wondering how I could get an image I was working on in 300 dpi, there and back and not lose resolution. I felt so dumb when I found out about the whole DPI myth and how it was/is tied to legacy printers, etc.
I still get people losing sleep over this stuff so I’m going to link a site with a ton of info on it. There are a TON of other sites online. If you want more opinions, just google:
72 dpi
72 dpi myth
The DPI Myth
…etc.
All About Digital Photos
http://www.rideau-info.com/photos/index.html
The Myth About DPI
http://www.rideau-info.com/photos/mythdpi.html
How to Properly Change DPI
http://www.rideau-info.com/photos/changedpi.html
I hope this helps clarify.
I found this little known fact out first hand when I was first experimenting with different tone mapping operators a few years back. I was testing out the various softwares that will take your bracketed shots and “Merge to HDR” to create either a .hdr or .exr. Turns out the act of merging to a High Dynamic Range Image using bracketed images, can be and IS unique amongst the various apps on the market.
The process the application goes through to merge to hdr is not as standardized as I thought it would (or should be) and is slightly differently with various apps (done under the hood with their code). Hence the reason that merging raw files to save in one app and then opening that .hdr or .exr in another app could and can does lead to different results than just using that 2nd app to merge and then tonemap the same files. One would think that it should be a standardized formula that would lead to the same .hdr / .exr. But as it turns out… different chefs make different dishes despite starting out with the same ingredients.
So the next time you are planning to use an application to provide automation (merge to hdr for dozens of folders) using one app, then tonemapping those .hdr / .exr saved files in a totally different app… you should know what the tendency of the original app you are using to merge “tends” to do (create). Color, saturation, etc…
Just a little HDR tip to close out the 2009 year.
I’m not starting a war over this, but I would like to shed some light here. Hell, I think the concept needs to be tonemapped to reveal the details in the shadows (blatant pun intended).
Anyone have any online resources linked they can send me? I’m looking for links online that explain what tonemapping is as well as why tonemapping is necessary for 8bit viewing and printing. [[[ HINT: Anything viewable on the web or in print is NOT hdr. ]]] If you didn’t even know this much then the links I post from users or an example I create myself if necessary will hopefully shed some light on the matter.
I’d rather not recreate the wheel and just link to current resources. If there are none out there that clarify the concept for mere mortals then I’ll have to do so myself (only if necessary). It needs to be simple enough so that my mom can understand. She can barely use a DVR so she is my ultimate technology challenged litmus test. If you have a link that cuts through technical jargon, send it to me and I’ll post it.
No comments on this post. Send the links through my contact page (use navigation above).
If I don’t get responses or if the links provided to me can’t be understood by my mom, then I guess I’ll have to step up to the plate and create an example myself… but I’d love to save the time and just link to current resources.
