People often ask what the difference is between a silver and a white beauty dish. I have heard it said that beauty dishes are designed to be white, and that silver beauty dishes are a marketing department afterthought. Others say that silver dishes are more contrasty, and have more 'snap,' and so have their place in the photographer's studio.
The Maxwell Renderer is quite accurate at simulating the behavior of light. I thought it might be instructive to use the Maxwell Renderer to investigate the differences between a highly polished near perfect mirror-coated beauty dish (which as far as I know does not exist in the market), a typical silver beauty dish, and a white one.
To reveal the light paths, I ran a wall right through the center of the dishes, bisecting them in half like wall sconces. The virtual beauty dishes are ellipsoids - squashed hemispheres. They are not scientifically designed. The light is placed within the dish by eye, not at any special focal point, and no particular brand of beauty dish is being emulated here.
Remember: these are virtual tests. Not real ones. You may, nonetheless find them worthwhile to see.
click thumbnail above to enlarge
click thumbnail above to enlarge
click thumbnail above to enlarge
UPDATE 9/30/2009
Walter Melrose with mola-light.com on Silver Beauty Dishes
"A silver surface is much cooler in colour temperature and tends to add a cyan cast....The silver surface does not allow the light to follow the contours of the reflector as they were intended. Although the silver surface gives the impression of greater output it does not apply to function, our white surface is 90% reflectance and very efficient."
I remember this quote from the primary source, the Mola site, but right now I can only find secondary references to it on flickr and photo.net
Skeletal Pegasus street art on the remains of a ghostly Mobil (?) station on La Cienega near La Tijera and LAX. I have since learned this is the work of 'skullphone.'
(I added his URL to the photo, using Photoshop's 'blend if' to tuck the type seemingly behind the chain link fence. It's essentially a luminance matte.)
Folders are not just a place to stash messy piles of layers. Folders also help Photoshop users organize layer composites a bit more like what is possible in programs like Shake.
This is a 16-bit Photoshop environment. Because I am summing two relatively bright layers, I have overexposed and clipped the photograph.
Once the values go over 65536 (256 in 8-bits), they are lost, and dimming them later cannot recover them.
If I drastically overexpose in a 32-bit composite, as I have above, I still seem to clip above white.
But I can still recover the 'lost' information.
Photoshop's 32-bit environment is different from its 16- and 8-bit versions. In 32-bits there are not simply more divisions between black and white, there are values far outside those limits.
I'm not sure why Photoshop doesn't do all its math at 32-bits internally and then just cast to 16- or 8-bits at output. I'd use the 32 bit environment more often, but for some reason not everything works in 32 bits.
There is a fair amount of discussion on the internet in one forum or another about how to do this, ever since it was done for The Aviator.
What follows is not as involved as one of the somewhat more complex implementations described elsewhere, but I put this together as an experiment.
The basic idea:
A) Multiply the Red Sep by RED
B) Make a group; set the group blend mode to Normal, not Pass Through (important) - In the group, screen the Green and Blue Seps together and multiply them by CYAN.
C) Add the results of (A) and (B) using LINEAR DODGE (or Screen, if you like. Same result in this particular case)
------------------ UPDATE:
I took another look at the process. I felt the skin tones were taking to great a loss in saturation, and the whole image was being dominated by the cyan contribution.
Instead of adding red to a cyan-tinted 'sum' of green and blue, I'm adding red to a cyan-tinted 'average' of green and blue.
------------------ UPDATE:
This is a work in progress. I re-jiggered the file one more time, replacing the 'sum of half red and half green' with the essentially equivalent 'half of the sum of the two' a/k/a the average of the two. To avoid clipping in the sum, I went to 32 bits. I like the exposure adjustment layer. I think the exposure plus the gamma provides nice control over the look.
In future I'll probably derive the channels by adding the channel mixer into the workflow instead of manually loading the channels as selections and pasting white through them onto black layers.
------------------ UPDATE 5/22/2009
I got some promising results using the black and white adjustment layer to build color images.
Red record dyed cyan and combined 'subtractively' (muliplicatively) with a strict cyan record stained red. By 'strict' cyan I mean I used a black and white adjustment layer set to accept cyan, but reject green and blue.
Two Strip Technicolor (Subtractive Method)
Red record dyed cyan and combined 'subtractively' (muliplicatively) with a more 'permissive' cyan record stained red. By 'permissive' cyan I mean I used a black and white adjustment layer set to accept cyan, and green and blue in equal amounts.
UPDATE 6/30/2009
click photo to enlarge
This (what if) experiment in yellow-blue 2-strip technicolor made me think this was an error: The coral cake frosting rose is getting turned yellow, instead of surviving the yellow filter with much of its coral still intact (red should survive a yellow filter). This is because everything is getting turned gray before being filtered yellow. Interesting, but is it a mistake? Maybe not. These separations did get recorded to black and white film first. I wish I could see more examples of the real deal instead of digital recreations.
You can really see the effect of two colors on one strip in action here. Fast moving objects color fringe. Darks decompose into cyans and reds. Where the two overlap (are multiplied - if digital) darkness results in the positive image.
In 2006, the BBC ran a series of programmes called The Lost World of Friese-Greene. The series, presented by Dan Cruickshank included The Open Road Claude Friese-Greene's film of his 1920s road trip from Land's End to John o' Groats. The Open Road was filmed using the Biocolour process, and the British Film Institute had to use computer enhancement of the original print of the film to remove the flickering problem.
* To mask a layer with an alpha: go to the alpha channel you want. Click on it while pressing the 'control' key on a PC. That should load the alpha channel as a selection. Now with the selection still loaded, ask for a layer mask on the layer you wish to mask. It will materialize with the selection already punched into it. Finally, hit control-i on a PC to invert the layer mask, which is a necessary step in following along above.
So 'subtractive color' might be better called 'multiplicative color.'
If the color match in this example isn't perfect, I plead RGB <-> CMYK gamut and Photoshop color management and colorspace issues.
UPDATE 6/2/2009
According to Getting It Right in Print by Mark Gattner, the K in CMYK was not chosen because it disambiguates from the B in Blue. The K in CMYK stands for 'key,' as in 'key plate,' the plate (often with the text) to which the other colors are registered.
UPDATE 6/15/2009
An in depth look at the linear equations and non-linear lookup tables that more closely approximate the RGB to CMY conversion can be found in Digital Color Halftoning by Henry R. Kang
I've derived theoretical C, M and Y plates from the RGB channels in the previous entry on Additive Color Mixing.
To achieve the cyan plate, I took the red channel, negated it, multiplied it by full (255 0 0), then inverted (color negated) the result. I did the analogous steps with the green and blue channels to derive theoretical magenta and yellow color plates.
The blend mode between each derived color plate is MULTIPLY.
The layered .psd file is here if you'd like a closer look.
Now lets simplify the Photoshop file. I merge the layers in sets of 3 starting from the top so that we can get a plain look at these theoretical CMY plates.
Cyan, Magenta and Yellow color ink plates on white paper - with a multiply blend mode between each.
Here is the layered .psd file if you'd like a closer look.
So what is with this 'theoretical' word, anyway? And why only CMY? Where is the K?
Good questions. I'll try Photoshop-produced CMYK plates next...
UPDATE 6/1/2009
Actually CMY is not just theoretical, now that I think about it. Color motion picture film is 'subtractive' CMY - no K. So this mimics the behavior of color motion picture film.
An in depth look at the linear equations and non-linear lookup tables that more closely approximate the RGB to CMY conversion can be found in Digital Color Halftoning by Henry R. Kang
Here is an RGB image. RGB is additive color. Can you guess how to mix the RGB color separations to produce the image?
You add the three color separations together. In Photoshop, the blend mode for adding is LINEAR DODGE.
(You can also use SCREEN in this case, since the R, G and B channels are completely independent of each other, SCREEN and LINEAR DODGE produce identical results)
Inspired by an online conversation I had with photographer Steven Eastwood, I just wanted to record here a few remarks I had made on the nature of the '5-eye line.'
You can really see the 5-eye-line in the beauty shot above that was taken from a distance with a long lens. The sides of the model's head are evident.
In the wide-angle closup shot, the '5-eye line' is almost a '3-eye line,' and the side planes of the model's head are no longer visible.
When you shoot using your camera in a vertical aspect ratio, you don't do anything special but turn your camera. To match Maya to your DSLR you need to make an extra little adjustment. When you swap the resolution x and y, you have to swap the horizontal and vertical film aperture values as well...
Here is a rectangular polygon mesh just the right size and shape to fit into a Maya camera resolution gate after it has been set to mimic a Nikon D200. (as described here)
A horizontal Nikon D200 full resolution frame is 3872 x 2592.
. . . if you simply change the resolution . . .
. . . and if you simply rotate your plane 90 degrees you'll see it still no longer fits . . .
You need to swap the values in the 'Horizontal and Vertical Film Aperture' fields as well. It may seem obvious, but it's easy to forget.
Another solution is to leave the 'Film Aperture' values as if for a horizontal camera match, and change the lens from a 50 mm (in this case) to (it turns out to be) a 33.5 mm lens. But who wants to do the necessary work to figure that out?
So to match a horizontal D200 to a Maya camera, don't forget to set the
Horizontal Film Aperture = 0.622047244, which is 15.8 mm in inches
Vertical Film Aperture = 0.929133858, which is 23.6 mm in inches
Then your Nikon D200 lens should match your Maya lens.
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A 'full frame' Nikon D700 has a chip size of 36 mm x 23.9 mm.
At 1.417" x 0.945" Maya's default camera back equates to 36 mm x 24 mm. So Maya default cameras equate directly to Nikon D700 lenses.
Don't forget to swap places with the 1.417 and the 0.945 values when you go vertical with the resolution.
A Nikon D200 uses a standard DX size sensor. (23.6 x 15.8 mm)
Maya's 'film' is described by two measurement: Horizontal Film Aperture and Vertical Film Aperture
According to Nikon's online documentation:
Horizontal Film Aperture and Vertical Film Aperture are the height and width of the camera's aperture or film back, measured in inches. The Camera Aperture attribute determines the relationship between the Focal Length attribute and the Angle of View attribute. The default values are 1.417 and 0.945.
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Now, why Maya uses the word 'aperture' to describe this should have been my first clue that something was wrong, but I always assumed that Maya's default camera mimicked 4-perf movie film, just like most people shoot and project. It would have been the obvious thing for them to have done.
Turns out I was wrong.
All these years Maya masked its values by expressing them in inches, and all these years I never bothered to check the math, but it turns out that Maya's default width, the mysterious 1.417 works out to be 36mm.
All these years Maya has been modeling an 8-perf camera as its default. As if it were a 'full frame' still camera like a Nikon D700 or a Canon 5D Mark 2
After I completed the image of Apnea - The Knife Thrower's Assistant, I realized the target looked previously unused. It needed a history of knife impacts. After trying to place impact holes manually, I realized I could create a Photoshop brush to scatter the holes around.
I used a stock Photoshop 'sponge' brush squeezed into a slit shape. I turned the scatter way up, and introduced some random rotation. Finally I added some noise and additional image processing to the scatter cloud to give some degree of unique shape to each impact hole, so they wouldn't all look essentially identical.
I used the pen tool for most of the edges, but I couldn't capture the hair with either the pen or channel masks, so I made my own edge by stroking pen paths with a single pixel brush.
I cloned some of the artificial hairs around to get sufficient quantity.
Locking transparency, I even cloned in existing hair color and sheen, and modified the hair style a little bit.
Note the edge of the yellow ring. Sometimes I apply additional surface 'modeling' post 3D render via Photoshop. After all, it's only a single image. It doesn't have to track or animate.
A tiki in a classic "Man in the Moon' crescent. I've never seen another. Could this be the first?
In spite of the hanging wires and irregular seams the image is completely computer-generated. The lighting approximates 'Rembrandt portrait lighting' and the fill is accomplished with a white off camerabounce card thanks to the radiosity of the Maxwell Renderer.
