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Additive colour mixture.

Additive colour mixing is based on the optical mixture of monochromatic (single-coloured) light in the spectral primary colours, blue, green and red. When the spectral primary colours are projected over one another in equal parts, they produce white. If two additive primaries are combined with one another, they will produce the secondary mixtures, yellow, magenta and cyan, which are, at the same time, "complementary" to the third additive primary which is not involved ( complementary colours; sub-tractive colour mixture). The first processes of colour photography were based on the additive principle of colour mixture. Today additive colour mixing is used, for example, in television technology and for filtering in minilab printers .

An additive colour mixture is produced by mixing together two or more sources of coloured light. The colorimetrist talks of combining different, individual colour stimuli ( CIE system) to produce a new colour sensation which differs from the single colour stimuli. The new colour sensation comes about through the projection of blue, green and red light on top of one another, or through the simultaneous (or apparently simultaneous) effect of very small, coloured elementary areas, which the eye is unable to distinguish because of the small area. A particular colour sensation can be created by additive mixing in a certain ratio (examples: coloured screen printing; excitation of coloured luminous dots by electron radiation in colour television).

Prism Converging lens - Fig. 1: Blue, green and red primary colours are made visible through a prism (simplified representation without secondary colours), and are then mixed additively again to give white light.

In the additive photographic processes, the blue, green and red primaries are produced from white light using appropriate filters (e. g. additive colour filtering in printers). The original is exposed successively behind blue, green and red colour separation filters onto the photo-paper. The desired colour can be controlled by varying the exposure times behind the individual colour separation filters.

Advanced Photo System .

At the core of the Advanced Photo System is the film, which differs from conventional 35 mm film with its narrower film format, a smaller film cassette (cartridge), and an extra magnetic coating. A distinctive feature of the film, which is available with 15, 25 and 40 frames, is the smaller negative (16 × 30 mm). The continuous perforation on conventional films has been replaced by two registration holes per negative. Three different formats can be selected:

• the small format (C = Classic) with the "classical" side ratio derived from the 35 mm format of 2 : 3
• the full format (H = High Vision or HDTV) with the side ratio of 9 : 16
• the panorama format (P) with the side ratio of 1 : 3

AHU layer.

The black AHU layer (in the B/ W films AGFAPAN APX 25/ 100/ 400 PROFESSIONAL and AGFA SCALA 200x PROFESSIONAL) offers particularly effective protection against haloing. The AHU layer (Anti-Halo Undercoat) is located between the emulsion layer and the base, and absorbs the light beams after they emerge from the emulsion layer. The more intense the tinting of the AHU layer, the better the protection against light scattering. Once the film has been exposed, the AHU layer has done its job, which means that its tinting can be removed during wet processing of the film.

The AGFAPAN 35 mm films feature an additional safeguard against haloing, namely a grey-coloured base for cutting down scattered light. With the AGFA SCALA 200x roll film and the AGFAPAN APX roll and sheet films, a dark-green anti-halo layer on the back of the base provides extra protection. The colour is removed from this layer too during wet processing.

Analytical densities.

The analytical colour densities are the individual emulsion densities of the developed component dyes of a colour film. They provide information about the dyes that have formed in the light-sensitive emulsion layers, and about the corrections that are necessary to achieve the colour rendition aimed at by the manufacturer.

Fig. 2: Absorption curves of the developed emulsion dyes of a reversal film with the total density curve on top. For example, the magenta dye component shows the highest colour density in the green spectral range, but also reveals undesirable secondary densities in the blue and red spectral ranges.

The measurements for determining the analytical densities are carried out by the manufacturer with the aid of specimens of individual layers, and in this respect constitute a rather special case of densitometric measurement. Normally, densitometric measurement is carried out on the developed multi-layer film ( spectral integral density).

The result of adding together main colour densities and secondary densities is the total density for the three main spectral areas, which is also known as visual grey or mean neutral density. With suitable exposure and processing, the total density is wave-shaped over the three density curves of the spectral analytical densities in a density range of 1.0.

Anti-halation.

The sharpness of a photographic image is negatively influenced, among other things, by two optical phenomena: diffusion halation and reflection halation.

Fig. 3: Diffusion and reflection halation (cross-section and top view of the film surface). The halo reflection is caused by light reflecting from the back of the film . The halo diffusion is caused by light scattering Emulsion .

A diffusion halo is caused by light scattering on the silver bromide grains in the emulsion layer. The extent of the diffusion halation will depend on the layer thickness and on the distribution and size of the silver bromide grains. It can be reduced by special emulsion additives (screen dyes) and by the use of thinner emulsion layers.

A reflection halo is caused by the total reflection of straight beams of light at the interface of media with different refractive indices, e. g. at the interface between emulsion layer( s) and the film base, and by further reflection at the film base/ air interface.

Effective protection against reflection halation can be achieved by dark-coloured anti-halation undercoats ( AHU), protective coatings on the back of the film (e. g. gelatine NC coating, NC stands for non-curling) and by colouring the base grey. The dark colour is removed from the anti-halation undercoat and from the back-coating during wet processing, but the grey colouring of the base remains.

ASA

Abbreviation for American Standards Association which specifies one of several units of measure for the speed of films. Doubling or halving the arithmetic ASA value is equivalent to doubling or halving the film speed. Together with the logarithmic DIN standard ( speed), the ASA standard is incorporated into the international ISO standard.

Browsers and Images .

Email browsers can accept attachments, which tend to stay with the message, at least as long as the message is retained in the recipient’s browser. Attachments are files, and users should be aware of a few issues with some kinds of files.

If a user wants to send or to archive the content of a web page into to (with all the “window dressing” images and secondary sidebar data), there is a way to incorporate all of the associated image files that accompany the basic HTM or HTML textual data. Microsoft has provided a program called Web Archive, a free download to users who have an installed Office 2000 program. With the desired HTM program name being displayed in Windows Explorer, do a right-click on the program name and a left-click on the menu item which says save as a Web archive. It takes a short while for the resulting MHT file to form. The MHT file can be used as a file that is easier to manage for archiving, and as a file that can carry the complete “dressed up” page as an email attachment.

Most modern web browsers and many other applications that are capable of displaying the more common image formats will support the viewing of animated GIFs. Note that animated GIFs will also display in the body of an email message.

JavaScript provides some interesting features in graphic displays that can be animated, interactive, etc. Note that JavaScript coding is contained with HTM files, and can be sent as email attachments. When the recipient chooses either Open file OR Save to disk, the HTM file will open in a web browser, and the JavaScript content will be displayed.

Email browsers tend to have the capability to insert picture files into a message. Those familiar with inserting stationery or colored backgrounds may be aware that if you use a small image as a background picture in an email message, it will replicate itself, tile fashion – to fill up the entire background of the browser screen. The commands are Format|Background, then use the small browser box to find the image file to insert.

A user can also send a picture (animated GIF, for example), as a direct picture image within the body of an email, in which case you get just one image in the message box. The commands are Insert|Picture – but note that to make Picture available as a menu item you must first set HTML format to apply to the message box of the composition window. You can place text in the message box and can position the image with some of the composing screen tools.

A person generally can capture individual image files from the net (usually an HTM or HTML file or its equivalent) by right-clicking on them and left-clicking on “Save Picture As,” which provides a dialog box for browsing for the desired folder in which to place it.

A person can always capture the content presented on the screen by using Alt + Prnt Scrn, which places the screen image data on a clipboard. They can then open MS Paint and do an Edit|Paste to import the image data into a temporary BMP form in MS Paint. If the user wishes to capture more than the image data shown on the screen, they can do so by modifying the effective “zoom” of their screen by selecting more pixels for the screen to display.

Most users have their monitors set to display at 800 x 600 pixels, and alternate settings may be selected, within the range of the values supported by by their video card and other aspects of their computer, which can include their operating system. To access these settings, open the desktop, right-click on any portion of the desktop background, left-click on Properties, click on the Settings tab, a small panel on the low right side of the this dialog box will say Screen area, and will have a slider that can be dragged left or right. If you wish to capture a screen that would contain about 10 inches of printed height, it is likely that you may do so if you re-set to 1280 x 1024 pixels. However, you may find a need to temporarily do away with the toolbars at top and bottom that mask the upper and lower edges of your screen. Such a function is available and is called Full Screen, which is accessed in View or Tools. To recover from a full screen presentation so you can access tools to proceed with other steps, you can press the Esc. button.

Fancy web displays often make use of Java Script files, which produce interactive images which can be embedded within HTM files. Java Script files will appear in web browsers, but not in email browsers.

Word 97 and Word 2000 readily accept images for insertion, and even allow you to re-size them when they are embedded. They can be positioned quite accurately if you know the tools and techniques for doing so. These Word programs can also view or create HTML files. Normally, an HTML file would open in a web browser. However, if you open the Word application first, then open an existing HTML file in the Word application, it will display okay.

Animated GIFs that are inserted into Word files act differently, depending on whether the Word application is viewing the Word file in the DOC format or in the HTML format. In the latter, the animated GIF remains animated, in the former, the GIF is not animated.

A user might have a reason to save a page layout as an image file. This is one of the options available in Publishing software. Multi-column Word fles with small text may not remain stable in their layout unless some strong measures are taken to make them more stable. The problem lies in a feature of how the specific width characteristics with proportional fonts is not retained. If the first column on a page grows to have additional lines dues to a few words that have expanded to create this change, the first column will not end at the designated place, as the bottom margin determines the last row of text to be accepted. The page can take on a most unfortunate upset of its layout.

Alternate means for obtaining stability is to take a “snapshot” of the displayed file by doing a web capture, as described above. This usually results in an image file that retains most of the clarity of the file as it was presented in the Word application. A user can import a word or text file into MS Paint, also with little loss of clarity. Another method is to create a PDF file by using an Adobe PDF Writer application. PDF does not display small point sizes of text with much clarity – also – PDF files are usually much bigger than Word DOC files. In each of the above cases, you lose the ability to edit the text in the new file format.

Kinko’s prefers to work with PDF files than with Word DOC files because they are more stable. Both file types carry the layout margins with them, but PDF files are better at retaining the exact text layouts.

An older or limited edition version of PDF Writer is included with all versions of Adobe Photo Deluxe, and usually gets installed unless you find a way to decline it. It may not be obvious whether you have it installed or not. The best way to check on its presence is to take an inventory of the “printers” installed on your computer. That’s where you may find the PDF Writer.

Chromogenic process.

Dye-forming (chromogenic) development is the basis of the AGFACOLOR process. It is a procedure which, during the development stage, generates a dye image consisting of the three subtractive colours ( subtractive colour mixture) in the individual emulsion layers at the same time as the silver image. The dyestuffs are insoluble in water and diffusion-resistant. They remain in the emulsion layer at the points where the silver image is located. After development the silver is bleached (converted into soluble silver salt) and dissolved out of the emulsion in the fixer. What is left is a pure dye image. During colour development, the oxidation product of the developer substance reacts (" couples") with the colour couplers dispersed in the emulsion layers to form the emulsion dyes, yellow, magenta and cyan, due to the spectral sensitisation of the individual layers for the blue, green and red spectral components of visible light. The chromogenic colour process, which is used for all modern colour films (and most printing materials), is based on the principle of subtractive colour mixture. At least three layers with integrated colour couplers are applied on top of each other, one sensitized for blue, one for green and one for red. The layer structure of colour films is, in reality, more complex, because there are other protective, separating and filtering layers in addition to the colour-sensitized emulsion layers containing the colour couplers .

During processing of these multi-layer films, the silver halide is reduced to metallic silver in the exposed areas of the photo-sensitive emulsion layers. The oxidation products of the colour developer resulting from this process react with the (colourless) colour couplers in the emulsion layers to give yellow, magenta and cyan image dyes. At the same time as the three black-and-white images in the individual layers, three dye images are thus created in the subtractive primary colours, which remain when the metallic silver is bleached out during subsequent processing. Depending on the type of film and process, the result is either a colour transparency or a colour negative.

In a slide, the colours of the subject are the right way round. When they are viewed through a projector, we see that part of the beam of light that passes through the transparency. The slide can also be printed onto special reversal copying material (or onto colour negative paper using the Agfa DigiPrint system). In a colour negative, on the other hand, complementary colours are formed. The positive image with the colours the right way round is obtained by printing onto colour negative printing material. The first patents for chromogenic development (1910 - 1913) stem from Rudolf Fischer.

CIE system .

In the human eye it is the retinal cones which allow us to perceive colour, in other words allow our eye to see the visible radiation in the range from approx. 380 to 750 nanometres (nm). There are three types of cones with different spectral sensitivity. As the basis for colorimetry, it is therefore adequate to have three primary colours, each of which can, in turn, be fully defined by three values (hue, saturation and brightness).

One such colorimetric system is the international CIE system (CIE: Commission Internationale de l'Eclairage). The representation of colours in CIELAB diagrams largely corresponds to the physiological perception of colour. Since all impressions of colour in the human eye are generated with just the three colours of light, blue, green and red (three-range division of the visible spectrum), the CIE system is based on the three primary colours, blue, green and red (as monochromatic, i. e. not additively mixed primary colours) with the wavelengths 435.8 nm (blue), 546.1 nm (green) and 700.0 nm (red). On the basis of comprehensive statistical investigations, these values were established as representing the colour perception of the "standard colorimetric observer".

Fig. 4: Example of a CIELAB hexagonal diagram; it shows the different colour saturations of three AGFACOLOR PROFESSIONAL negative films. The greater the distance from the neutral point, the greater the colour intensity.

The standard colorimetric system describes colours as vectors in a three-dimensional model (colour space). A radius vector originating from the zero point (or black point) is assigned to each chromaticity (type of colour). Each chromaticity thus has its own direction in the colour space. The radius vector of a given colour in the colour space is called the colour stimulus. A colour stimulus is the equivalent, expressed numerically, of the physiological sensation of colour of a "standard observer" with normal colour vision. The mathematical simulation of a radiation stimulus to the eye and brain converts this stimulus into a colour stimulus, which can be defined by three factors, e. g. hue, saturation and brightness. The vector properties of colour stimuli enable colours with two or more vectors to be additively combined from three fixed primary colour stimuli (according to the principles of vectorial addition).

The CIE system is an important scientific method of colour identification, because it is so close to the human perception of colour and because of the possibilities it offers for accurate mathematical treatment of spectrophotometric data. The complex vectorial representation in the colour space is replaced in practice by a simplified, two-dimensional representation of the colours, e. g. in CIELAB diagrams.

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