CFV Histogram

peterbkk

New Member
As I get more used to working with the CFV digital back (on my 205FCC), I am finding that the histogram display is a powerful tool.

I actually don't use the display on the back of the CFV to review the image. It is a bit too small for that. I find that I am quite happy using the viewfinder for framing, focus and DoF and do not need to review the image on the CFV back. I guess that this comes from years of shooting with film when it was often days before you saw the resulting images.

However, I am finding that, having a quick look at the histogram is a good way to make sure that the exposure is right. If it is sub-optimal, I can quickly adjust and shoot again. I am even starting to think like "the histogram needs to be pushed a bit to the right so I'll press the up button on the 205FCC's exposure controls a couple of times."

For example, yesterday I was photographing in one of Bangkok's old markets. These markets are partly roofed and partly open. So the light varies dramatically from one place to another. By using the 205FCC's spot meter then looking at the histogram after the shot was taken, I could ensure that I optimised the exposure for each image. When I loaded the images into FlexColor I found that using the histogram approach had significantly increased the quality of the images exposure settings.

But, one question occurred to me.

I know that it is important to keep the vertical bars of the histogram within the left and right borders of the histogram display. If the histogram is all jammed up to one side, then the exposure is probably wrong, especially if a lot of the vertical bars are right on one edge.

But, what about the height of the bars? Sometimes the height of a group of vertical bars appear to be taller than the histogram display area, disappearing out of the top of the rectangle. Is this a bad thing? Should I be trying to keep the top of the vertical histogram bars within the top boundary of the display? And, if so, how does one do that?

Regards
Peter
 
The height of the bars indicates the number of pixels at each level (0-255). Sometimes there are simply more pixels than can be counted on the screen. This is no problem whatsoever. What's important is to keep your data from clipping at either end. Here's an interesting experiment - try taking a picture of a gray card. If it is properly lit and exposed, your histogram will be ONE pixel line going up the middle, since all the pixels are the same value! And, of course, not all of them will be "counted" since the height of your screen does not permit it. You can even do this more simply in Photoshop. Open a new file, and fill it with any shade of gray you want, and then check the histogram - it will show ONE pixel line. Fun! If you want the line in the exact middle, choose RGB 128.
However, it is coming to light latey (no pun intended), that a "better" quality image can be obtained by keeping most of the data to the right side of the histogram, without clipping. Luminous Landscape has a great article on this matter which explains in detail "why" this works, and why it is crucial. In a nutshell, they explain that there is much more detail present, and far less noise, when most of your pixels fall to the right side. Shadows and darker areas can be fixed in post editing with much better results. The "scary" thing, is that your initial image looks somewhat overexposed, and all of us growing up in the transparency age know that overexposing a transparency is a cardinal sin. However, as long as you don't allow crucial detail to clip, you will be pleasantly surprised at how much better your final image will come out after post editing.
Michael H. Cothran
 

peterbkk

New Member
The height of the bars indicates the number of pixels at each level (0-255). Sometimes there are simply more pixels than can be counted on the screen. This is no problem whatsoever.
...
how much better your final image will come out after post editing.
Michael H. Cothran
Michael,

Thank you for this information and the suggestion about placing the majority of the histogram into the "brighter" section on the right. You are right, it certainly clashes with my 25 years of shooting transparency film. But, I will give it a go and see what happens.

IMO, one of the great benefits of digital is that I no longer have to care how many shots I have left on the roll or worry about the dwindling number of fresh rolls in the camera bag. So experimentation is encouraged...

Regards
Peter
 
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