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From analogue to digital in fine monochrome |
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Page 5 of 9 |
When we use Photoshop or other image editing software for monochrome, it is important to realise that all we can do in this software is alter the brightness value of individual pixels or groups of pixels in an image with a given resolution to change the appearance of the final picture. Nothing else - just alter the brightness value of pixels. The number of brightness values available to alter is an absolutely critical issue in producing fine monochrome images. That leads us to the way we acquire, or ‘capture’, the original image as a digital file. At the time of writing, a few digital cameras provide a reasonably high resolution monochrome (known as greyscale) file to be able to produce a good quality medium-sized print. However, as a generalisation, none are capable of really fine quality large prints, and none provide the high resolution ‘high bit’ (see below for an explanation of that phrase) file essential for extensive monochrome manipulation in Photoshop. Though digital cameras are bound to arrive soon that will do this for us, the only real way to do it at the moment is to photograph the original image on to film, then to scan the resulting negative or transparency. Currently, film cameras are much cheaper anyway, especially since we probably already have an outfit, and we similarly already have plenty of negatives. We don’t need a digital camera to start. Scanning - why 16 bit? In their various forms, scanners - film or flatbed - in monochrome read the brightness value of the negative (or transparency) inserted in them at very fine intervals across their area. They do this in ultra-fine steps, each step being a row of the mosaic pixels in our digital image, and at each step they take a reading of the negative’s brightness value at each of those pixel positions. Each position’s brightness value is recorded in the file as a binary number. We can set the number of positions per inch at which the scanner reads these separate values in advance, known as the scan resolution, up to the maximum capability of the particular scanner. This is normally described in ‘dots per inch’ or dpi. That’s really confusing, because it sounds like inkjet dots - tiny dots each surrounded by white space. There aren’t dots like that. This is a mosaic made up of tiny adjoining squares, each with a separate brightness value set by the average brightness value at each of the positions at which the scanner read the negative. The more positions at which the scanner reads, the more the mosaic squares possible, and the higher the resolution. I prefer to refer to this process of reading the positions on the negative as ‘sampling’ each position. So they aren’t dots per inch, but samples per inch in my mind. Next Page >> |
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