Photographic pixel

The fineness of the grid pattern, called resolution, is quantified in terms of pixels per linear distance. Common practice for commercial quaUty images assumes that photographic images can be reproduced accurately using about 300 pixels per inch (120 pixels/cm). 

Digital lithographically processed TFT arrays having 128 x 128 pixel with 75 dpi resolution were fabricated directly on the PEN. Figure 11.15 shows a photograph of the completed flexible array. The I-V transfer and output curves for a typical TFT pixel (W/L x 1) within the array are shown in Fig. 11.16. The device has on/ofF ratios of >108, sub-threshold slopes of 0.5 V decade-1, and field-effect mobility of... 

Figure 15-4. (A) Example of a photograph with a resolution that is too low for print, so the pixels show as squares, instead of blending to show tones. (B) A similar photograph with a true resolution of 300 ppi.

The resulting computer-processed image, as viewed on a video monitor, is a mixture of green (for porosity) and black (for non-porosity) pixels. The green pixels can be counted and divided by the total pixel number to give the porosity of the section under view. The video binary image can then be fed to a flat-screen TV for photographing. 

Scattered patterns from polymers may be photographed using a Polaroid instant camera (Polaroid Land Film Holder 545). The scattered intensity can be quantitatively monitored by means of a two-dimensional Vidicon camera (1254 B, EG G Co.) coupled with a detector controller (Model 1216, EG G Co.). The analogue simal is digitized and analyzed on an DMA 111 (Optical Multichannel Analyzer) system. The scan rate is typically 30 ms for one-dimensional scan and about 0.5 to 1.5 s for two-dimensional mode depending on the number of pixels chosen for grouping. 

The decay-time constant Tae,short of the fast component is mainly from the motions of the phenylene protons, whereas Tae.iong for the slow component depends on the motions of the methyl protons. The parameters of such a biexponential analysis for each pixel lead to four images, one for the spin density, which is given by the sum A -I- B of the amplitudes of both exponentials, one for each of the relaxation rates of the exponentials, 2e short 2e,iong respectively, and one for the difference A — B of the amplitudes of both exponentials. The spatial distributions of the first three of these parameters are shown in Fig. 10.3.8(b)-(d). The contour-level image (b) of the spin density provides information only about the different thickness of the sample. Here the shear band is hidden. But it becomes visible if the relaxation rates are evaluated. In agreement with the photograph (cf. Fig. 10.3.5(b)) the shear band runs from the upper left to... 

Fig. 13. A photograph of the operating 10 x 10 pixels of p-i-n PHOLEDs made by the H-dipping method at 15 V on a glass substrate (10 x 10 cm2).

The second criterion of quahty is the depth of color of a digital photograph. This depends on the number of colors encoded for 256 colors, eight digital characters (bits) per pixel are necessary. A color intensity of 16 bits enables 65 536 colors to be represented, which is known as high color . An almost photographically reahstic representation ( true color ) is only possible with 16.7 miUion colors, and this requires 24 bits per pixel [121]. 

Figure 14.10 Optical scheme for a spectrophotometer with an echelle grating. For clarity only the central section of the beam issuing from source 1 is represented (this beam should cover the whole mirror 2). The echelle grating 5, separates the radiations arriving from the source in the horizontal plane (in x). The prism then deviates the radiation in the vertical plane (in y). The path of three different spectral lines is shown. The images of the entrance aperture 2 are in the focal plane 8. In the past, to detect these radiations, photomultiplier tubes (PMT) of reduced size were installed in specific places, but now charge transfer devices (charge coupled or charge injection devices, CCD/CID) are used, as an electronic equivalent of photographic plates. This allows a continuous spectral cover from 190 to 800 nm with excellent resolution. Sensors of 500 X 2000 pixels (each 12 x 12p,m) are now used.

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