Frequency Distribution Graph / Histogram

ullanta

ullanta

Veteran
Frequency Distribution Graph / Histogram - does anyone fully understand this?

Certainly, I have the general intuition, and indeed in many situations find it useful for focusing. But I'm not sure what exactly it represents, and how to use it in selective-focus situations.

What are the axes of the graph?

Does it represent the whole image? The center of the imagte? In a selective focus situation, how do I know what PART of the image is in focus? That is, if I wan one small part of my image to be in sharp focus, (how) does this tool help me?

Thanks!
-Barry
 
I have found that the shallower your dof is the less acurate the indicator becomes. I myself would like to see the evf detail function use a colored outline like canon uses. I wonder if this could be added in a firmware update?
 
Edweirdo said:
I have found that the shallower your dof is the less acurate the indicator becomes. I myself would like to see the evf detail function use a colored outline like canon uses. I wonder if this could be added in a firmware update?
Click to expand...

I didn't know Canon use this feature, I know that it is used in JVC ProHD cameras though. I find the colour outline confusing and only use the peaking feature on my JVC because it seems to really show the edges up.
 
I'd say the horizontal axis is Frequency ... and the vertical some kind of pixel count (like a histogram).

The idea is that fine detail in an image is represented by higher frequency signal. So, if you have your subject basically in focus, then tweak it to perfect focus, you'll see more high frequency pixels appear as the object's detail increases.

Feel free to correct me if i'm wrong anyone!

Lee
 
That definitely sounds plausible - I get my two HMC150s at the end of the week and can't wait to try them out.
 
FFT = Fast Foureier Transform.

Basically it's exactly like a Spectrum analizer for audio.

You can convert any signal into frequencies. The sharper the image, the higher the frequencies.
Imagine a resolution chart with lots of fine lines. The frequency of the lines is very high. A chart with wider lines has a lower frequency.

The X-axis of the chart is frequncy... higher frequencies to the right (just like an audio analyzer. And the Y-axis is amount (volume) of that frequncy.

So the more of the graph on the right, the more higher frequencies are present, and threfore the sharper the image is over all.


A histogram works the same way ... execpt that X is brightness (instead of frequncy).


- Mikko
 
Hey Mikko, one thing I don't understand though is how does the camera know which part of the frame I'm trying to focus on?

I can see how this method would work shooting 28mm at F5.6 but how does the histogram/spectrum display know what you are trying to focus on with the long end of the lens at F1.4?
 
You must log in or register to reply here.
Back
Top