dba

can someone tell me what threshold,amount and pixels to use,for posting pics on the web and also for just tweaking my own pics? whats do they all mean? cheers

AndyC_772

iTrader: (2)

Unsharp mask is a way of increasing the differences between adjacent pixels to make fine details stand out more clearly. The effect, when applied properly, makes the image appear sharp and pleasing to the eye. When overdone, however, it can give images a processed, digital look that's rather offensive. Most digital cameras apply some USM to every image before writing it to the memory card - and those that don't tend to produce images that look rather soft until they have had USM applied manually.

Threshold is the minimum difference that has to already exist between two adjacent pixels for the filter to be applied at all. A low threshold ensures that even the slightest details will be boosted - but a very low threshold can exaggerate small amounts of noise in large, plain areas like a blue or grey sky. I typically use a threshold of 2.

'Pixels', otherwise known as radius, determines the size of the circle around each pixel in which the filter takes effect. So, for example, if a given pixel is very bright and the radius is set at 1, all the neighbouring pixels (but not those any further away) will be darkened so as to make the bright one stand out even more. With the radius set at 2, not only will the pixels neighbours be darkened, but their neighbours will be darkened as well. The value to use here depends on the image and how sharp it is to begin with - any values over about 1.5 quickly start to make the image look artificial.

Amount is the strength of the filter - the amount of lightening or darkening that's applied to each pixel depending on the difference between that pixel and its neighbours. Experiment with values between about 80 and 150.

Note: these numbers refer to the dialogues in Photoshop - other tools may scale numbers differently.