Digital Photoguide

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Part 4 - Exposure

November 2004 Magazine


Part Four of Digital Photoguide describes the important factors to bear in mind when taking a digital photograph.  For example, when should you use Jpeg, Tiff or Raw format ? What are the benefits of auto-exposure compared to manual ?

Histogram
The most important “new” feature in a digital camera compared to its film equivalent is the histogram. This is a display of the range of brightness values – also known as Levels – in the captured image. After taking a picture, the histogram together with the miniature image displayed on the camera allows you to assess the exposure and judge whether any corrections are necessary. Understanding the histogram and “Levels” is probably the most important concept in digital photography and is relevant to both taking the picture and, especially, the processing of images afterwards on a computer.

The nature of today’s digital cameras means that, to maximise image quality you should avoid over-exposure. The article in the magazine explains how to judge exposure based on the histogram and gives an example of a picture with near-ideal histogram. The picture in question is of 37047 on a weedkiller train at Whyteleafe South and is reproduced here.

Pt4-37-Weeds

The image has an excellent range of brightness values and will require minimal manipulation, either to produce a very nice print or to display on a web page. The version of it shown here has had no changes made to its Levels (i.e. affecting brightness or contrast) just slight sharpening. Strictly speaking, sharpening does make a small change to contrast but the change is insignificant on this particular image. If it does not display well on your computer, your monitor may well need to be calibrated. See Digital Photoguide Part Two for an explanation of monitor calibration. The additional work needed to be done on this image depends very much on personal taste, and probably only a very slight darkening is required in order to make the colours slightly richer.

 

Part Three

 

Part Five


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