I discuss ISO and other related topics (aperture, shutter speed, histogram, and so on) in my recently completed an introductory photography book: "A Concise Introduction to Photography."
ISO is a measure of the sensitivity of your film or digital sensor. In this episode I discuss the basics of ISO and how it relates to exposure and noise.
Custom White Balance is the process of setting the neutral gray reference point manually, rather than relying on your camera’s Auto White balance (which typically only approximates neutral grey.) Custom WB is an important step for anyone who is serious about achieving accurate colours in their images. If you are shooting RAW single images, then you can just take a picture of a spectrally neutral grey card and set the WB in post-processing. However, if you are shooting JPEG or Video, it is important that you set the custom WB in your camera before shooting. How you do this is dependent on your particular camera, but it will involve taking a picture of the gray card (fill the frame as much as you can) and then telling the camera (via its menu system) to use that image as the neutral reference point. You will have to read your camera’s instruction manual for the particular details of those simple steps. Now, once you have the Custom WB set, you will likely have to manually rotate the WB dial or indicator from AutoWB to Custom WB. (Again, the specifics will vary for each camera manufacturer. Once you have that stuff set, you are good to go shoot your videos without having to worry about trying to do onerous colour correction in post-processing. Good luck!
The histogram is a graph which represents the distribution of light or luminance values in your image. Its horizontal axis ranges from black and dark shadows on the left to bright or pure white on the right. Although there is no 'perfect' distribution for a histogram, a well-exposed image will have luminance values that fall within the histogram's range for your camera, with no pixel's luminance values falling on the extreme left (shadows recorded as black) or on the extreme right (highlights recorded as white), unless you are trying to achieve a particular creative result. Fortunately, all modern digital cameras can display an histogram, which you should check early and often to help ensure that you achieve a good exposure. To view the histogram, preview your image on the LCD screen of your camera, and flick through the options until a graph appears (some cameras only show luminance, while others also show the Red, Green, and Blue channel values). If it shows values on either extreme, you may want to adjust your aperture, shutter speed, or ISO, and then retake the image to regain that lost information.
If the brightness values in the scene fall outside of you Histogram's range (i.e., outside of its dynamic range) even after making appropriate exposure adjustments, then you may want to properly expose for the shadows and highlights in separate images, and then combine or blend those exposures in an image-editing software program like Adobe Photoshop or Photomatix; this technique is also called HDR, or High Dynamic Range photography.
Special thanks to Wen Zhang