Special functions on your camera – Histograms
Discover something new about your DSLR that will help you take even better photographs than you already do!
You knew that little graph that pops up on the preview screen when you press the Info button by mistake while viewing an image? Well, that’s the histogram, and it’s very, very important! In fact, it’s more important aid useful than the preview image itself and if you really want to become a master photographer you need to start paying attention to the histogram display.
The problem with only looking at the preview image is that it may not be giving you a true picture of what the sensor has recorded. If you’ve accidentally set the screen brightness too high or too low. For example, the image you see will look brighter or darker than it really is. So you adjust the exposure to compensate ard end up introducing exposure error that wasn’t even there. The same applies when shooting in poor light or really bright light, when the screen may not be accurate.
The histogram provides a much more accurate and useful means of assessing the exposure of a digital image because it shows you the way the tones in that image are distributed aid also tells you if you’ve over- or underexposed it Here are the key facts about histograns:
1) The left side of the histogram is the shadow, the night side is the highlight and the middle section covers the midtones.
2) Most shots will have a histogram shaped like a hill or a mountain with a high point in the middle (midtone area) and slopes down to the shadows (left) and highlights (right).
3) If your scene consists mainly of dark tones, the histogram will be shifted over to the left towards the shadow side. However, a histogram weighted to the left can also indicate underexposure if the scene or subject has average tonality or is bright.
4) If your scene has mainly light tones, the histogram will sit towards the highlights on the right. A histogram weighted to the right can also indicate overexposure, though, if the scene or subject has average tonality or is dark in tone.
5) If the histogram collides with the left (shadow) side, this indicates that some shadow areas have been underexposed and will come out black – which means no detail has recorded in those areas.
6) If the histogram collides with the right, (highlight) side, this indicates that some highlights have ‘blown out’ due to overexposure and will come out white with no detail recorded. If you enable your camera’s Highlight Warning you’ll be able to see if any highlights have blown out because the areas in question will “blink”.
7) Generally you should avoid blown highlights or blocked shadows, but in some situations you won’t be able to so don’t panic. Creatively, both ‘errors’ can work well if you want a high-key or low-key effect. If you don’t, then you need to reduce or increase the exposure to make the image darker or lighter, then check the histogram again.
8) Important! Your camera’s sensor records far more tonal information towards the right (highlights) side of the histogram than the left (shadows) side. In fact, it records more tonal values in the right-hand 20% than the rest of the histogram put together. So, if you shoot Raw and want to achieve optimum image quality, aim for part of the tonal graph to fall into the final 20% of the histogram on the right. Often this means the image will appear overexposed on the preview screen, but you can adjust the exposure during post-production. Overexposure is always preferable to underexposure with digital imaging -providing you don’t blow the highlights!