Histogram - what for?

hello,

I've never really understood what purpose the histogram in the upper left corner serves. Could someone give me a good explanation why I need to use this, and how? Thanks.

-Al.

Hi,

Histogram is a graph that shows the distribution of light within your photos and therefore a very useful tool to verify whether your photos are well exposed or not, independently of whether you are using a profiled monitor/screen or not.

The left side of a histogram represents the darker part/tones of a photo. The middle represents the middte tones and the right side the lighter tones.

Generally a well exposed photo would have a histogram, which looks like this. The light is well distributed within the whole range of the histogram.



Underexposed looks like this. The darker/left part is very dominant.



And overexposed - the right/light part is dominant, whereas the dark part is non-existent.



Of course this is only a general rules. There are photos, in which the histogram is very right oriented but are still well exposed, e.g. high key photos, or photos which mostly contains light color and via versa -> low key photos.

And what about the IRGB function in the Histogram window? what additional information can I gain from that compared to the regular Histogram explained above?

cheers,
PhotoWebber

The IRGB-Tab shows you all three channels (red, green and blue) at the same time with different colors.

OK. Thanks. And is there also a rule of thumb how the IRGB-Histogram should look like for a good picture?
Above was explained, that the Histogram of a well exposed photo should look similar to a sinus curve. But what if I shoot a picture with lots of blue sky and a blue sea. There will be probably only few green and red parts in the IRGB-Histogram, i.d. no sinus curve distribution for all three colors but only for the blue part, right?

cheers,
PhotoWebber

Hi, this could be the case. But there is no real general rule for this, as it depends on the color mixture. At least I do not know any

Most colors consist of RBG. So in a dominant blue photo, unless it is pure blue, you will still find more green and red then you might expect. So more probably is that either all 3 channels have a sinus curve, but the amplitude of the blue one is signicantly higher than the other's or they are just differently distributed, e.g. the dark part is dominated by red and green, while the light part by blue...etc...

Best regards

Hoang-Tran