Calculation of contrast for computer simulated resolution chart image

The work is devoted to the analysis of the resolution chart image created with the Image Simulation mode of ZEMAX software. The changes in image quality are simulated using the model of Helios-44M-4 photographic objective lens. The research is conducted for monochromatic light conditions and computer simulated resolution test chart as an object for the lens with different chart positions. An axial beam and an off-axis beam that corresponds to the maximum object space field angle are analyzed. The calculation of contrast of the simulated resolution chart images is made modeling different spatial frequencies of the chart lines. The contrast is calculated in three ways. The first way uses the maximum and minimum values of the image illumination, and the second and third ways are based on the integral values of the illumination of black and white lines, calculated with the method of rectangles and the method of trapeziums, respectively. Having been calculated the values of contrast are compared with the theoretical values of the diffraction modulation transfer function obtained with ZEMAX.

Impacto do uso de diferentes materiais na função de transferência de modulação em imagens radiológicas

O avanço da radiologia digital proporcionou uma melhoria significativa à qualidade das imagens radiológicas. Essa evolução trouxe muitos benefícios para o diagnóstico por imagem como a agilidade do processo, a melhoria da resolução espacial, a diminuição do tempo necessário de exposição, entre outros. Os últimos trabalhos publicados mostraram que a função de transferência de modulação ou MTF (Modulation Transfer Function) é a técnica mais adequada para avaliar a resolução espacial das imagens digitais, pois apresenta um resultado quantitativo mais preciso. O objetivo deste trabalho é avaliar o impacto do uso de diferentes materiais para a determinação da resolução espacial através da MTF. Foram utilizadas diferentes espessuras de placas de alumínio (Al) e cobre (Cu) para a aquisição da imagem de uma borda. A MTF foi avaliada pela técnica da função de propagação de borda ou ESF (Edge Spread Function) usando o plug-in COQ do ImageJ. Foi possível concluir que uma variedade de espessuras de alumínio são aplicáveis para a determinação da resolução espacial através da MTF, assim como uma placa de teste de colimação.

General Modulation Transfer Function Fitting Equation for Human Eye with Contact Lens

In this research, a general equation was derived to represent the modulation transfer function (MTF) of the human eye with the presence of the contact lenses (CL) and during the vision with monochrome or multi-wavelength (polychromatic) light. This equation was used to fit the MTF's curves for the eye with pupil diameters (EPD) (2.5, 4, 6, and 8 mm). The fitting equation accuracy was revealed by using the standard deviation (STD). The results indicated that the image MTF is sensitive to (EPD). Moreover, eye vision degrades as (EPD) increases due to the increased spherical and chromatic aberrations. The new equation consists of two exponential terms in addition to a correction polynomial function (H) to fit the EPD effect. The results showed that H function with power two is sufficient to give a good accuracy when the EPD is less than 4 mm, while H with power five is necessary when the EPD is larger or equal to 5 mm. The equation gives a high accuracy also in the case of vision with white light for the eye with a contact lens.

The size-of-source effect in thermography

In thermometry, the displayed temperature value of an object depends on the size of the object. This behaviour, also known as the size-of-source effect (SSE), might be a major cause of measurement uncertainty in a thermoscene. The SSE is caused by diffraction, scattering, reflection, aberration and digitization in the optoelectronic propagation path. The influence of diffraction and digitization (sampling and pixelization) can be described advantageously with the modulation transfer function MTF. The system MTF of an uncooled camera is determined by the diffraction in the lens (optical MTF) and the averaging of the radiation over the pixel area (pixel MTF). If the system MTF is known, the contrast reduction and, thus, the SSE can be calculated. Especially with very small objects, e.g. hotspots creating an image covering less than 4 pixel × 4 pixel on the focal plane, the displayed temperatures are much too low. When imaging large objects, such as area blackbodies, not only the edge areas are affected, but also the entire image. Finally, the contrast reduction by the MTF is explained by means of a complex scene (Siemens star).