Saturday, April 19, 2014

The Histogram

Incorporating the The Histogram into an ACDSee Pro 7 Workflow

This is the first in a series of articles where I provide a tour of the important raw development tools that ACDSee Pro offers. I'm not sure how many articles there will be in all.  It would seem this is a MUCH bigger task I have set myself than I originally thought.  Some of the future articles may wind up as video tutorials if that seems appropriate.  Part 2 of this series has been published and can be found here.

NOTE: While the comments specific to ACDSee Pro 7 are obviously unique to ACDSee Pro 7, the information and knowledge base on which those instructions were created are common to ALL editors and workflow tools. Non ACDSee users might well find that information useful. 

Please assume I am working in raw, and in the “Develop Tab” of ACDSee Pro 7. In many ways, the bit mapped edit tab offers greater control of lighting. But the use of raw among “serious” photographers is so great that I feel that is the best use of our time. 

Furthermore, we need to produce the best image possible from raw before creating a tif or jpg file of a photo before sending to a bit mapped editor. So if we CAN produce that quality photo in the “Develop Tab”, I think we should.

Exposure is a complex issue in post processing. It is more than merely making sure that the image isn’t TOO bright, or TOO dark. It also touches on tonality and color. Light is the foundation on which photography rests. If a photographer can’t control how that light is used, he or she can’t control how his or her images are perceived.

It is beyond the scope of this article to discuss how to get a good exposure with your camera. Post Processing control is complex enough. But any photographer is wise to learn all he or she can about getting a good initial capture. That makes post processing tasks much easier.

The uninspiring photo below will be our test photo for this tutorial.

The Histogram and Clipping View Toggle Switches

These controls reside at the top of the Develop Tab’s control window. The Histogram toggle is on the left, and the Clipping View Toggle is on the right (See image, immediately below)

The Histogram Icon and Control

This control’s Icon is blue when the Histogram is displayed as gray when not displayed, but since you can always see the histogram, when displayed, the color doesn't matter much, I guess!

The histogram is a reflection of all the changes you make to a given photo. There are three channels displayed as a line chart on an X-Y axis. It displays the number of pixels for each value of the selected channel. The vertical axis represents the number of pixels and ranges from zero to the highest number of pixels in the graph. The horizontal axis represents the value of the selected channel, from 0 to 255. 

Actually the maximum number can be greater than 255. “255” is the value for an 8 bit color depth color space such as found in jpg and other 8 bit images. Tiff and raw images can also be created with a 12, 14, or 16 bit color depth. And the broader the color depth, the number of shades of color is is increased exponentially. I have found though, that thinking of a maximum number of 255 seems easier to comprehend and doesn't affect the accuracy of how I use the histogram. 

Note that as the controls change, the histogram changes as well. 

The left portion of the histogram describes graphically how much of the photo is in the shadows.

The right portion of the histogram describes graphically how much of the photo is in the highlights.

The center portion of the histogram describes graphically how much of the photo lies within the mid tones.

The histogram is one of the most useful tools ACDSee offers that I have ever ignored up to this point. It is useful in that it allows you to better understand the complex relationship between light, dark, tonality, and color, without letting the emotional, artistic content misdirect your attention. 

As we work through the controls, I will continually refer back to the histogram to illustrate and help explain the changes that occur when the controls are set.

One thing I have noticed from writing a similar article for Corel Paint Shop Pro, is that histogram configuration is not universal. While the principles and goals of all histograms remain the same, how the developers of their respective programs choose to implement and display that photo information graphically can vary widely. 

If you are using a product other than ACDSee Pro, you will have to experiment a bit to understand how the publisher of your software chooses to display histogram information.  The principles I present in this article will likely remain true, however the detail will be a bit different.

My advice is to set your basic exposure information in one program, such as ACDSee Pro, and learn to use THAT histogram implementation well. If you leave the program that you have used to set exposure and lighting with a histogram and you feel the need to review the histogram, go BACK to the original program that you used to set your exposure with. Trying to interpret 2 or 3 different histogram implementations for the same photo can be confusing and lead to less than the desired results.

The Clipping View

This control’s Icon is to the right of the Histogram icon.  It is blue when the clipping display is turned on and is displayed as gray when not turned on. This color indicator is useful in that it isn’t always obvious when the display is turned on, so it is helpful to have this reminder.

This control can be activated either by mouse clicking the icon,or by pressing “E” on the keyboard.

Its function is to tell you what areas of your photo are either so dark or so light that no detailed information can be displayed or seen by the viewer. You may well think that you should be able to tell that bit of info, so why do you need an additional visual indication? 

It isn't always easy to see the clipped highlights and shadows on screen, and the correlation between the editing screen and a display screen or a print can vary widely. Things that you may not consider important at edit time might be very important at display time. This allows you to know this information with certainty.

Consider this Image. Other that straightening and cropping not editing has been done to it.

Note the Histogram, the shadows seem to be at their highest about ⅓ of the way from their absolute darkest. The highlights are not as high as the shadows, but at their peak, they are about ⅓ of the way from the absolute brightest. Now consider how I torture this photo:

I moved the contrast control all the way to the right. Note how anything that could be considered in the shadows is green, and much of what can be considered a highlight is red. What this means is, that anything that is now green has lost all detail, it is solid black, and anything in red has ALSO lost all detail, it is solid white. Also note how there isn't very much that isn't red or black, meaning those areas still have some detail in them.

But NOW, compare the two histograms above. In the first photo, there was a lot of area under the curves in the rough middle of the chart, but in the second, the level of the curves is very low in the middle and the curve at the absolute left show significant growth where before it was non-existent. A similar occurrence appears on the far right. Though smaller than that part of the curve on the left, a bigger area has no data at all than before.

What does all this mean? By sliding the contrast to the right, I increase the contrast. This is done by brightening the light areas as much as possible and by darkening the dark areas as much as possible so that both extremes lose any detail in them (solid black or solid white). That low level of curves that remains in the middle are those areas too dark to go fully white, and too bright to go fully dark. It is these areas that will show any detail. 

Below, see what the altered photo looks like without the clipping tool activated.  Not very pretty, is it?

Don’t worry, I won’t be showing this many before/after photos in subsequent articles, but I wanted you to see how these changes relate to the controls and how those changes will look like in a photo. And in the future, I will point out changes to to the Histogram as I address the various controls.

I hope you find this interesting and look forward to your comments.

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