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Also known as objects in some software programs. These are really useful when building up an image. Each layer is like a sheet of plastic or glass that can be laid on top of each other. Areas that have pixels block pixels from the layers below and areas that are clear let the pixels show through from lower layers. Layers are used to create complex collages and add repositionable text and graphics. More advanced programs have Layer blend modes that allow pixels on one layer to react with ones on layers below.
The Foveon X3 direct image sensor is a new technology that works like film. Foveon pioneered the development of the direct image sensor using advanced developments in semiconductor design, image processing, and signal processing. Their X3 sensor directly captures red, green, and blue light at each point in an image during a single exposure. Similar to the emulsion layers used in colour film, Foveon X3 image sensors have three layers of pixels. The layers of pixels are embedded in silicon to take advantage of the fact that red, green, and blue light penetrate silicon to different depths - forming the first and only image sensor that captures full colour at every point in the captured image.
A printing process that separates a color image into cyan, magenta, yellow and black layers. Film is made for each colour which is then used to make printing plates for each colour ready for the printing press.
Reciprocity law states that as you increase the intensity of light reaching the film you also need to decrease the speed it reaches the film by the equivalent amount. Most films work quite happily between exposures of 1/2sec and 1/1000sec, but go beyond these extremes with a very low intensity of light and a long exposure or a very high intensity of light and a correspondingly short exposure and the law fails an exposure increase may be required when the shutter speed is beyond these limits. At these extremes the law fails. Compensation is required to adjust for this, but there is no strict rule to correct the error. Most film and paper manufacturers provide technical details on request with a rough guide to exposure adjustments. As a rough guide for an exposure of one second you would increase the speed to two seconds, or open the aperture by one stop. A speed of 10sec would need to be increased to about 50sec or open the aperture up two stops. With black & white film you only have to worry about this exposure correction, but with colour film does not only suffer from exposure problems but also colour casts. A colour film is made up of three individual colour layers, each layer suffers from reciprocity failure at different levels. On an uncorrected film the shadows may have a magenta colour cast but the highlights may suffer from a cyan cast. To correct the cast not only would a longer exposure be needed but also the inclusion of a colour correction filter of a low value, care would have to be taken in choosing the correct filter otherwise an over corrected result may appear.
One of the most versatile Alternative Processes, Gum Bichromate was invented in 1855, and became popular at the turn of the century. The process takes advantage of the fact that colloids, such as gum, gelatine and glue, when mixed with a bichromate, become hardened and insoluble when exposed to light. By mixing a coloured pigment in with the colloid, and then washing away the undeveloped areas with water, you are left with an image in the dye. Exposure times using daylight will be typically between 30 seconds and 2 minutes. Advanced Gum Bichromate workers build up a number of layers of varied pigment colours by re-sensitising, re-exposing and re-developing prints.