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PostPosted: Sat May 31, 2008 1:50 am 
I just had some general questions about histograms and the rule of thirds...what are they?? I always see histograms on camera displays and I think it has something to do with the brightness of the photo but I have no idea how to read it. Also, how will grid displays help me? I've heard they can be used for this rule of thirds that I am also unsure about. Sorry if these questions were posted by someone else in these forums, I couldn't find them.


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PostPosted: Sat May 31, 2008 3:13 am 
Hi acoustic335,

The tic-tac-toe grid divides the images in to thirds both horizontally and vertically. There is this theory in photography, that the four intersections between the lines are..for lack of a better word.."points of power" in an image.

It's claimed that more tension, energy and interest in the photo can be created by aligning to these intersections. E.g the nearest eye in a portrait, the an animal in a field etc.

It is based on, Pythagoras' theory of the golden mean - also known as the golden ratio, golden number or divine proportion.

The color histogram is a representation of an image derived by counting the 'color' of each pixel. The idea was proposed by Michael Swain and Dana Ballard in 1991. They are built from images in various color spaces - in DSLRs the RGB space, but it applies to CMYK and any other.

What they tell us as photographers:
There are a lot of insight into an image that can be gleaned from a color histogram, however it's most often used to detect whether an image is over or under-exposed. Or rather, how many of the pixels in the R G or B channel that are.

The histogram represents all pixels in the image, so it tells us how many of the pixels are over- or underexposed.

If there is a tall spike in the extreme left of the histogram, it's an indication that there are areas of the image that is underexposed and if it's on the right, it might be overexposed.

Cheers :-)


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PostPosted: Sat May 31, 2008 12:38 pm 
Hi accoustic335,

Further to what LahLahSr has said, have a look at this rule of thirds article and this histogram page at Cambridge in colour.

Mark


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PostPosted: Mon Jun 16, 2008 9:44 am 
nice link,

does the histogram just relate to colour and exposure?

If shooting in raw mode then im guessing an inbalance in the exposure could be fixed with post processing.

If you shot something in jpg and the histogram was sckewed would you try and fix it later or shoot again?


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PostPosted: Mon Jun 16, 2008 10:17 am 
You could fix an incorrectly exposed histogram after shooting in JPEG, but there is always much more scope for doing any post-processing in RAW. I would only shoot again if the shot was important enough, or if it absolutely could not be saved. Remember it is easier to recover lost shadows than blown highlights, so if in doubt, underexpose.

I believe the first link I gave you was about reading histograms for tone and contrast - have a look at this tutorial which explains how histograms can be used to show luminance and colour.

Mark


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