NCPS News

Brian Turnbull began this 2nd Digital meeting by invoking the spirit of Trafalgar – He had been press-ganged into his “Presenter’s” position. The rest of us invoked another Nelsonian touch and turned a blind eye to his protestations. Was Brian an ACDSee to Nelson?? No. Apparently ACDSee was not a Rank but a program given to him with his printer. It was a great help in both reviewing his pictures and in filing them appropriately in his computer. From the Thumbnails of the pictures he could select them and copy and paste to the appropriate folders, or sub-folders. Since one could be profligate in taking pictures it soon became necessary to evolve a good filing system to be able to easily find them again.

Brian wanted to stick to the basics. He dealt mainly with Levels and Curves.

The Levels curve (histogram) illustrated the tonal range in an image. Using the gradient tool he had produced a strip image going uniformly from black to white which, he explained, should give equal amounts of all intensities and a square (flat) levels graph. Using the Posterization filter the number of intensity values could be changed and this be reflected in the number of teeth in a comb-like levels histogram.. Adjusting the Brightness slider moved the whole curve up or down the horizontal axis.

The Curves graph did not show the tonal range but did show the effect of moving the levels sliders (black point, white point and intermediate slope (contrast). Adjusting the Brightness of an image lifted the whole Curve.

The Curves graph plots Outputs corresponding to individual brightness (intensity) Inputs. It begins as a straight-line slope of 45 degrees indicating that the output is the same as the input for each of the 256 levels. But the output can be modified at each level to increase or decrease the output at that input level. This allows image manipulation way beyond that possible with the Levels histogram ( Brightness, Contrast etc sliders). Brian demonstrated the weird effects of inducing complex Curves. Though a basic 8-bit system only allows 256 levels, Brian noted that the human eye cannot differentiate beyond about 200 levels.

After tea the audience was able to relax as Brian showed a variety of images taken around the back streets of Manchester. Some were of transient Graffiti and some of old buildings that were not likely to exist much longer in the modern Manchester.

Another good evening enjoyed by a packed room.

Home News News Index Report About us Syllabus Exhibition Results Service Newsletter Galleries Links		2nd Digital Evening 1st November
		Brian Turnbull began this 2nd Digital meeting by invoking the spirit of Trafalgar – He had been press-ganged into his “Presenter’s” position. The rest of us invoked another Nelsonian touch and turned a blind eye to his protestations. Was Brian an ACDSee to Nelson?? No. Apparently ACDSee was not a Rank but a program given to him with his printer. It was a great help in both reviewing his pictures and in filing them appropriately in his computer. From the Thumbnails of the pictures he could select them and copy and paste to the appropriate folders, or sub-folders. Since one could be profligate in taking pictures it soon became necessary to evolve a good filing system to be able to easily find them again. Brian wanted to stick to the basics. He dealt mainly with Levels and Curves. The Levels curve (histogram) illustrated the tonal range in an image. Using the gradient tool he had produced a strip image going uniformly from black to white which, he explained, should give equal amounts of all intensities and a square (flat) levels graph. Using the Posterization filter the number of intensity values could be changed and this be reflected in the number of teeth in a comb-like levels histogram.. Adjusting the Brightness slider moved the whole curve up or down the horizontal axis. The Curves graph did not show the tonal range but did show the effect of moving the levels sliders (black point, white point and intermediate slope (contrast). Adjusting the Brightness of an image lifted the whole Curve. The Curves graph plots Outputs corresponding to individual brightness (intensity) Inputs. It begins as a straight-line slope of 45 degrees indicating that the output is the same as the input for each of the 256 levels. But the output can be modified at each level to increase or decrease the output at that input level. This allows image manipulation way beyond that possible with the Levels histogram ( Brightness, Contrast etc sliders). Brian demonstrated the weird effects of inducing complex Curves. Though a basic 8-bit system only allows 256 levels, Brian noted that the human eye cannot differentiate beyond about 200 levels. After tea the audience was able to relax as Brian showed a variety of images taken around the back streets of Manchester. Some were of transient Graffiti and some of old buildings that were not likely to exist much longer in the modern Manchester. Another good evening enjoyed by a packed room. Bill Chadband
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