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From analogue to digital in fine monochrome |
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The digital image file: There is a basic principle we need to grasp about digital images before anything else makes sense. That is that the image is made up like a mosaic. For a given image area, the mosaic can be coarse with just a few mosaic ‘tiles’ so that they are very obvious, or it can be incredibly fine with so many tiny mosaic ‘tiles’ within the same given image area that they simply merge in the human eye and appear to be a smooth unbroken surface. The coarse mosaic is known as low resolution, and the fine mosaic as high resolution. Of course if we now took that same high resolution area and enlarged it, the point would come where the ‘tiles’ would begin to show as separate. By convention in digital imaging those tiles are known as pixels - that is an abbreviated compound of picture elements. (Confusingly, computer monitor screens also have pixels, but they aren’t the same thing. So ignore those for now.) Our aim in fine digital work is always to finish with a digital file with a high enough resolution to allow it to print without those separate pixel ‘tiles’ being apparent to the human eye - so that it looks like continuous smooth tones. Normally, the human eye will see an image of 300 pixels per inch (ppi) in its final reproduction size as smooth continuous tone. Having more pixels per inch isn’t necessary because we won’t be able to see any difference. Below 300 ppi, we increasingly begin to detect those separate ‘tiles’, pixels, so that the quality of the image begins, literally, to break up. So, in its simplest form a digital image is described by a file of numbers in computer memory that record the location of each one of those separate tiles within the two-dimensional image area - their co-ordinates. In monochrome, each of those pixels needs another piece of information described by a number - what shade of grey each one is, that is its brightness value. They can be any shade between absolute black and absolute white, so each pixel co-ordinate in the image file will also record the brightness value of that co-ordinate. Colour would need the hue/saturation of each co-ordinate too; monochrome needs only a brightness value. Next Page >> |
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© Barry Thornton Page 4 of 9 |
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