We describe a simulation of the complete image processing pipeline of a digital camera, beginning with a radiometric description of the scene captured by the camera and ending with a radiometric description of the image rendered on a display. We show that there is a good correspondence between measured and simulated sensor performance. Through the use of simulation, we can quantify the effects of individual digital camera components on system performance and image quality. This computational approach can be helpful for both camera design and image quality assessment.

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Digital camera simulation.

Small unmanned aircraft vehicles (UAV) are potential remote sensing platforms for precision agriculture. However, to be useful for in-season management, nitrogen status needs to be estimated sufficiently early in the growing season. To determine when differences in nitrogen status of irrigated potatoes could be detected, an experiment was established in 2013 with a randomized block design with four N fertilization rates and three replicates. Over the growing season, a small parafoil-wing UAV was used to acquire color-infrared images with pixel sizes between 20 and 25 mm. Two normalized difference spectral indices were determined from image digital numbers, the normalized difference vegetation index (NDVI) and the green normalized difference vegetation index (GNDVI), which were then calibrated using reflectance-based NDVI and GNDVI. Unexpectedly, there were decreases in the NDVI and GNDVI calibrations with increased camera exposure time. After calibration, both NDVI and GNDVI were about equal to indices calculated using reflectances from high-altitude aerial photography and the WorldView-2 satellite. During tuber initiation and early tuber bulking, differences in measured leaf area index (LAI), chlorophyll meter values and spectral indices were only detectable at the lowest N fertilization rate. Later in the growing season, all N treatments could be distinguished in the imagery, but too late to mitigate yield losses from N deficiency. Linear relationships between plot GNDVI and NDVI were hypothesized to differ among N treatments because there would be less chlorophyll content per leaf area. Contrary to the hypothesis, there were no differences among fertilization rates on either of the two sampling dates. Compared with alternative technologies, small UAV platforms and sensors may not provide value to farmers for in-season nitrogen management.

Monitoring nitrogen status of potatoes using small unmanned aerial vehicles

Many creative ideas are being proposed for image sensor designs, and these may be useful in applications ranging from consumer photography to computer vision. To understand and evaluate each new design, we must create a corresponding image processing pipeline that transforms the sensor data into a form, that is appropriate for the application. The need to design and optimize these pipelines is time-consuming and costly. We explain a method that combines machine learning and image systems simulation that automates the pipeline design. The approach is based on a new way of thinking of the image processing pipeline as a large collection of local linear filters. We illustrate how the method has been used to design pipelines for novel sensor architectures in consumer photography applications.

Learning the Image Processing Pipeline

THIS second part of Dr. Vogel's well-known hand-book is the fourth edition, completely revised and enlarged, as we are informed on the title-page. With the index it runs to 367 pages, and is embellished with numerous figures and a coloured frontispiece illustrating the Vogel-Kurtz process of printing in three superposed colours. The result is very satisfactory, and the grapes, pineapple, lemon, and other fruit appear very natural. There should be a promising future for this chromolithographic development of photography, which, it may perhaps be not altogether unnecessary to state, has nothing to do with the great question of direct photography in natural colours. Handbuch der Photographie: II Theil: Das Licht im Dienste der Photographic und die neuesten Fortschritte der photographischen Optik. By Prof. Dr. H. W. Vogel. (Berlin: Robert Oppenheim (Gustav Schmidt), 1894.)

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The Optics of Photography

JPEG baseline coding is a popular basic image compression technique. The JPEG-3 image compression is an extension of
standard JPEG image compression which uses a quality factor to scale quantization table. In order to achieve high
compression rate, the JPEG-3 image compression uses lower quality factor. The lower bit rates of image compression using scaling factor will degrade the visual quality on the images being compressed. This paper proposes a high compression scheme based on psychovisual threshold as an adaptive image compression. The comparison between JPEG-3 image compression using the typical quality factor and an adaptive psychovisual threshold has been done. The experimental results of an adaptive quantization tables based on psychovisual threshold show an improvement on the quality image reconstruction at the lower average bit length of Huffman code.

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An Adaptive JPEG Image Compression Using Psychovisual Model

A digital camera is a complex system including a lens, a sensor (physics and circuits), and a digital image processor, where each component is a sophisticated system on its own. Since prototyping a digital camera is very expensive, it is highly desirable to have the capability to explore the system design tradeoffs and preview the system output ahead of time. An empirical digital imaging system simulation that aims to achieve such a goal is presented. It traces the photons reflected by the objects in a scene through the optics and color filter array, converts photons into electrons with consideration of noise introduced by the system, quantizes the accumulated voltage to digital counts by an analog-to-digital converter, and generates a Bayer raw image just as a real camera does. The simulated images are validated against real system outputs and show a close resemblance to the images captured under similar condition at all illumination levels.

K. Venkataraman

Papers

Digital Camera Imaging System Simulation