Scanning hardcopy non-metric images is one of the most important sources in digital mapping. Low-cost scanners are still widely used in many applications as they can produce digital images of comparable precisions to ...Scanning hardcopy non-metric images is one of the most important sources in digital mapping. Low-cost scanners are still widely used in many applications as they can produce digital images of comparable precisions to those produced by expensive professional scanners. Yet, inexpensive scanners introduce geometrical distortions in the measured image coordinates that must be assessed and compensated before using their products for further analysis. In this article, several 2D-to-2D transformation models were investigated to calibrate flatbed scanners with different resolutions and sizes. We evaluated the potential of each model using two gridded-crosses plotted on high-quality transparent sheets. Control coordinates were provided through a photogram-metric analytical plotter. After scanning the sheets, least squares matching was applied to determine the precise locations of the crosses. By comparing the control coordinates and those estimated from digitized images, it was found that the mathematical model based on the projective transformation gives the best results for standardizing the geometric properties of flatbed scanners. The results show that scanning resolution of 2400 dpi achieves the requirements for large-scale mapping applications.展开更多
In this work, a method to reduce increase in optical density (OD) caused by multiple scanning in radiochromic film dosimetry in combination with a flatbed scanner is presented. Gafchromic EBT3 films are scanned with E...In this work, a method to reduce increase in optical density (OD) caused by multiple scanning in radiochromic film dosimetry in combination with a flatbed scanner is presented. Gafchromic EBT3 films are scanned with Epson Pro 1680 Expression scanner and time intervals of 15 minutes and 30 minutes are observed between consecutive scans to reduce the increase in temperature of the scanner. The maximum variations in OD after consecutive scans are calculated and compared to the values obtained for scans without interruption. For film irradiated to 3 Gy, a time interval of 15 minutes between two successive scans leads to a reduction of the OD increase of 56.2% compared to when films are scanned without interruption. Reductions of OD increase of 86.72% and 78.72% respectively for film irradiated to 1 Gy and 2 Gy are obtained when a time interval of 30 minutes is left between two successive scans. These results show that when time intervals are observed between consecutive scans, the increase in OD has significantly reduced. However, the method has the drawback of increasing the time needed to perform radiochromic film dosimetry.展开更多
文摘Scanning hardcopy non-metric images is one of the most important sources in digital mapping. Low-cost scanners are still widely used in many applications as they can produce digital images of comparable precisions to those produced by expensive professional scanners. Yet, inexpensive scanners introduce geometrical distortions in the measured image coordinates that must be assessed and compensated before using their products for further analysis. In this article, several 2D-to-2D transformation models were investigated to calibrate flatbed scanners with different resolutions and sizes. We evaluated the potential of each model using two gridded-crosses plotted on high-quality transparent sheets. Control coordinates were provided through a photogram-metric analytical plotter. After scanning the sheets, least squares matching was applied to determine the precise locations of the crosses. By comparing the control coordinates and those estimated from digitized images, it was found that the mathematical model based on the projective transformation gives the best results for standardizing the geometric properties of flatbed scanners. The results show that scanning resolution of 2400 dpi achieves the requirements for large-scale mapping applications.
文摘In this work, a method to reduce increase in optical density (OD) caused by multiple scanning in radiochromic film dosimetry in combination with a flatbed scanner is presented. Gafchromic EBT3 films are scanned with Epson Pro 1680 Expression scanner and time intervals of 15 minutes and 30 minutes are observed between consecutive scans to reduce the increase in temperature of the scanner. The maximum variations in OD after consecutive scans are calculated and compared to the values obtained for scans without interruption. For film irradiated to 3 Gy, a time interval of 15 minutes between two successive scans leads to a reduction of the OD increase of 56.2% compared to when films are scanned without interruption. Reductions of OD increase of 86.72% and 78.72% respectively for film irradiated to 1 Gy and 2 Gy are obtained when a time interval of 30 minutes is left between two successive scans. These results show that when time intervals are observed between consecutive scans, the increase in OD has significantly reduced. However, the method has the drawback of increasing the time needed to perform radiochromic film dosimetry.
