That Cheatin’ Histogram

Let’s look at what happens when we take a picture with our DSLRs. The exposure meter in the camera is using reflective light instead of incident light so a man’s tux will show a different meter reading than a bride’s dress even if the exposure for both of them was correct since the white dress will reflect more light than the tux, thus throwing the exposure meter out of whack. Secondly, when we press the shutter the camera creates a JPEG image with all of your picture settings and an S-Curve applied. Yes, this happens even if you are shooting in RAW mode since the display on the LCD is actually the JPEG image which is also the image the camera uses to calculate the histogram. I can’t count the times that my exposure meter was dead center, the preview looked great, and the histogram was good but when I brought up the RAW image in Lightroom, the image wasn’t quite exposed as well as I expected. Anyone who shoots a lot can attest to this issue. Yes, your LCD and histogram are usually accurate enough, but if you want to be accurate all the time then you need a reading from the point of few of the subject by measuring the actual amount of light hitting the subject and not the amount of light reflected by the subject.

What does a light meter tell you?

I asked a handful of photographers who had never used a light meter what they thought a light meter would tell them and surprisingly few actually knew even the basic functions of all light meters did with “Measure the light I guess” being the top answer. Even the most basic of light meters will allow you to set the ISO speed you want to use, then you set the shutter speed or aperture to what you want to use and the meter will give you the correct settings for a proper exposure. More fancy ones can also fire your flash equipment and some will even calculate the amount of flash versus ambient light.

Let’s say we have a nice bright sunny day and we set our ISO to 200, and our aperture to f/16, if we take a reading we will probably get something like 1/200th of a second as our shutter speed for a good exposure. With most digital light meters you can then make adjustments to the shutter or aperture and it will change the values on the screen to tell you what to change the other setting to.

If you aren’t familiar with the relationship between ISO, Shutter Speed, and Aperture, you should read the article we have about it (Link: The Exposure Triangle).

Testing the theory

Ok, I am sure many of you are skeptical that your camera, even a high end pro-series camera isn’t going to be dead-nuts accurate, but let’s take a few tests and see what our camera is telling us.

The following is a series of images of a product that has a black front and a light top, not something a camera’s meter is going to be good at so it will help illustrate the point well. Simply adjusting the camera’s settings to center the camera’s exposure meter at ISO 200, f/5.6 the camera gave us a setting of 1/400th shutter speed. Shooting the gray side of a WhiBal card it changed to 1/400th of a second, and shooting the gray/white/black side we got a setting of 1/640th of a second. By doing this test we can see that the camera’s exposure meter is going to change based on how reflective the subject is. In each image you can also see Photoshop’s histogram to see where the image’s exposure actually came in at.

Image 1 – ISO 200 f/5.6 1/400th – Slightly Underexposed (Based on WhiBal Gray)

Image 2 – ISO 200 f/5.6 1/640th – Underexposed (based on WhiBal White/Black/Gray)

Image 3 – ISO 200 f/5.6 1/200th – Showing good exposure (based on light meter)

Now some people may say that a perfect exposure should be centered in the histogram, however, digital sensors retain more detail in the highlights than they do in the shadows so you actually want your highlights to be fairly far to the right without going into the last little bit of the histogram which is exactly what we got with the final image.

But how does the meter know what the background is?

One of the most commonly asked questions is how does the meter know what the background of the subject is, since that should affect the exposure right? Well, let’s just try some experiments and see what we get. The following images were taken using the exposure settings provided by the light meter which were identical for both images, take a close look at the histogram for each image.

ISO 400 f/4.0 1/125th – Properly Exposed yet histogram says its underexposed

ISO 400 f/4.0 1/125th – Properly Exposed yet histogram says its overexposed

Of course the white paper is providing some bounce light that is providing more details around the edges and since I only metered for the center of center of the phone. So yes, the background can affect the exposure because you may not be metering for any reflected light, although this is typically only a problem with a situation like this. If I wanted to expose for the edges, then I could have metered at the edges. Does this mean the background affected the exposure? Yes, but only because the background in this situation actually is acting as a light source that is reflecting light into the edges around the product.

Will a light meter work properly in every situation?

So far we have looked at using a light meter for incident lighting, where this can break down is with highly reflective surfaces or in situation where the lighting is uneven, in this case a reflective meter is going to be more accurate. Most all light meters can do both types by adjusting or moving the light sensor dome. In reflective mode, the meter is going to act just like the meter on the camera.

Like anything else, a light meter is just another tool that is designed for a specific purpose. Used properly, it can dramatically improve your exposures and you camera setup time. The following image was taken in bright daylight with a large diffuser to the camera right and a large beauty dish flash to camera left. Combined with the ambient light, that is three different light values. With the light meter getting a reading taken at the subjects face, and the meter facing the camera, the settings provided were certainly dead on.

Model: Taylor Thorne

Ok, I want one, what do I do?

Light meters, especially used ones can be had for pretty reasonable prices. I see meters like the Sekonic L-358, which is a pretty nice meter with lots of functionality, often sell for $150-$200 on Craigslist. Cheaper models with less features, but still fully capable can be had for as little as $50-$60.

Model: Taylor Thorne

Pixel Blender: http://labs.adobe.com/technologies/pixelbender/
Pixel Blender Plugin Download: http://labs.adobe.com/downloads/pixelbender.html
Pixel Blender Exchange: http://www.adobe.com/cfusion/exchange/

Cloning and Stamping tool Live Preview with Photoshop CS4 from Kerry Garrison on Vimeo.

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Most of these features can be added back to Photoshop CS4 by downloading the plugins from Adobe’s website (links below) or accessing them from the Goodies folder on the installation DVD.

Download Links

Windows:
http://www.adobe.com/support/downloads/detail.jsp?ftpID=4048

Macintosh:
http://www.adobe.com/support/downloads/detail.jsp?ftpID=4047

For more information visit John Nack’s blog at:
http://blogs.adobe.com/jnack/2008/10/where_did_extra.html

Photoshop CS4 Fluid Zoom and View Rotation from Kerry Garrison on Vimeo.

Content Aware Scaling in Photoshop CS4 from Kerry Garrison on Vimeo.

The Adjustments Panel

Working with adjustment layers has always been a serious tool for hardcore Photoshop geeks, now this has been made much simpler with a new adjustments panel. This can be used to easily adjust Curves, Levels, Hue/Saturation, Vibrance, and more. New On-Image controls allow you to adjust colors in the image without the guesswork of trying to match a complex color. The panel features a wide range of modifiable presets for each type of control and more than 20 preconfigured, customizable starting points are included.

New to the masks is the concept of Density and Feathering to control how much of the mask is used. This is a huge improvement from before where deciding you wanted more or less effect would require constant redrawing of the mask.

Improved Dodge, Burn, and Sponge Tools

If you are a big fan of the dodge, burn, and sponge tools, one of the big issues in the past is that they could sometimes affect the color underneath in odd ways. The new versions of these tools work in a much more natural way and help you to make the adjustments you want while retaining tonal quality.

Improved Image Aligning and Panorama tools

CS3 has some really good photo merge tools and panorama tools, but CS4 takes these tools to all new levels. The improved algorithms improve blending, vignetting, and geometric distortion which results in much better final images. The blending tool can take multiple images of the same shot using different focal points and combine them into a single image with a greater depth of field.

Content Aware Scaling

Ok, this is some wicked cool sh** right here. What happens when you want to scale an image that has people in it? The people can get severly distorted ruining the new image. With content aware scaling, you can size an image and retain the original sizes of key elements like people. Using this you could change a horizontal image to a vertical image and the people or key objects in it will look the same while scaling the remaining parts of the image in a very natural and usually undetectable way.  When you see this in action, you will simply be amazed at what it can do.

Fluid Canvas Rotation

If you use a Wacom tablet or just need to view the world a little differently, you can now easily rotate the canvas around to make it easier to work on a it. Rotating the canvas does not affect the rotation of the actual image, this is simply a tool to make it easier for you to work on images by being able to look at it from different angles.

Smooth Pan/Zom and Flick effects

Some people may think that the new smooth pan/zoom and “flick” effects are just for show, but as you begin to use them you will see how much nicer it is to smoothly zoom in and out of an image and be able to toss the image around as if “flicking” it with your finger. The built-in physics engine makes this new way of dealing with images much more natural.

Bridge

I have always hated Bridge, I’m not afraid to admit it, it was slow, real slow, painfully slow to start up and slow to use. Even on my new quad core system with a nice video card, I still didn’t like Bridge. But get ready you fellow Bridge haters, Bridge is one sweet tool now. Not only is Bridge faster, but it has been improved in a number of areas. There are several new views such as Carousel view which makes working with large numbers of images signifigantly faster. Bridge now also has a PDF-based contact-sheet creator and preview along with web gallery tools. Bridge has certainly grown up and is more integrated into the majority of the CS4 tools besides just Photoshop.

Camera Raw 5

Take the Develop module tools from Lightroom 2.0 and put them all into Camera Raw and you now have Camera Raw 5. And I do mean virtually all of the tools like port-crop vignetting, the gradient filter tool, and the local adjustment brush tool. Unfortunately, Lightroom Develop presets are not available in Camera Raw.

Smarter Smart Objects

Smart Objects were introduced with CS4 and made a huge impact on how you dealt with new objects. With CS4, Smart Objects can now accept perspective transformations.

64 Bit Support (Windows 64 ONLY)

As a HUGE shocker to long time Macintosh users, the advantage this year goes to 64 bit Windows systems. Apple changed a bunch of things without telling Adobe and thus Adobe had to pull 64 bit support out of the Macintosh version. Are Mac users going to have to switch to Vista 64? Not really, only the heaviest of users is going to see much of a performance difference according to sources at Adobe.

Live Preview for Clone Stamp and Healing Brushes

As cool as the cloning tool and healing brushes are, the results have always been somewhat black magic, you just never really knew what you werew going to get. The new versions of these tools provide a live preview for easier and more precise cloning and healing results.

Availability and pricing
Adobe Photoshop CS4 Extended is now available in North America for an estimated street price of US$999. Adobe Photoshop CS4 will be available for an estimated street price of US$699. Both can be obtained directly from Adobe or through Adobe Authorized Resellers.

To order directly from Adobe, visit the Adobe Store at www.adobe.com or call
1-800-833-6687.

Licensed owners of Photoshop CS3 Extended, Photoshop CS2, or Photoshop CS can upgrade to Photoshop CS4 Extended for US$349.

Licensed owners of Photoshop CS3, Photoshop CS2, or Photoshop CS can upgrade to Adobe Photoshop CS4 for US$199.
Licensed owners of Photoshop 5 or 6 can upgrade to Photoshop CS4 Extended for $899 or Photoshop CS4 for $599.
Licensed owners of Photoshop CS3 Extended, Photoshop CS3, Photoshop CS2, or Photoshop CS are also eligible for special upgrade pricing to certain editions of Adobe Creative Suite 4.