Aalderink, B.J., Klein, M.E., Padoan, R., Bruin G., & Steemers, T.A.G. (May 2009). Clearing the Image: A Quantitative Analysis of Historical Documents Using Hyperspectral Measurements. Poster presented at the Book and Paper Group of the AIC 37th Annual Meeting, Los Angeles, CA.

Multispectralcamera

Of course, the discussion of aperture and depth of field is far broader than this, but these two photographs make a great jumping-off point for a detailed discussion of the basic concepts.

Aperture is the opening in your camera lens which determines how much light the camera lets in. With everything else being equal, a wide aperture creates shallow depth of field, and a narrow aperture creates a wide depth of field. Some cameras allow you to preview depth of field on the LCD. Others have a depth of field preview button which allows you to see the actual depth of field on the screen.

When I finally found my photography composition, I took a few shots to decide how much depth of field I wanted. I chose an aperture (f/4) that would allow me to smooth the details in the background as much as possible – while keeping the tree in the foreground nice and sharp.

And so, to summarize… select the nature photography composition that matches your artistic vision. Once you have selected the composition, determine which of the four variables you can use to best achieve the ideal depth of field to capture your desired image. Sometimes it may take a bit of experimentation and some time to find the correct combination. Be patient and remember that this is all part of the adventure. Make sure to have fun!

Ricciardi, P., J.K. Delaney, L. Glinsman, M. Thoury, M. Facini, and E.R. de la Rie. 2009. "Use of visible and infrared reflectance and luminescence imaging spectroscopy to study illuminated manuscripts: pigment identification and visualization of underdrawings." Proceedings of O3A: Optics for Arts, Architecture, and Archaeology II: 7391(July 2, 2009): 739106-1-12.

Fischer, C., and I. Kakoulli. "Multispectral and hyperspectral imaging technologies in conservation: current research and potential applications," Reviews in Conservation 7 (2006): 3-16.

RGBvs multispectral vs hyperspectral

The concave mirror is used when the light source is near the microscope (For example, an electrical lamp). Plane mirror is preferred when viewing an object via ...

I love aspens. Who doesn’t? But if you’ve tried to photograph trees, maybe you know that getting a shot you really like isn’t as easy as one may think. You pull out your camera in front of all that golden glory, and the resulting image just doesn’t do the scene justice.

To satisfy my goal with the aspens, I needed a high vantage point with trees growing below me. Standing on the forest floor would put me too low – I’d end up with ground in the photo if I pointed my camera downward or even straight ahead. In addition, I’d end up with sky in the photo – as well as distortion – if I angled my wide angle lens upward. No good.

For multiband imaging, we use a modified DSLR. Most DSLRs have IR-cut filters on the sensors that increase the quality of the visible light image by blocking any infrared radiation from the sensor. The modification of the camera we use included the removal of the IR-cut filter and the color filter array (CFA) allowing the camera to have a maximum sensitive of around 330nm to 1200nm and to acquire monochrome images.¹ The spatial resolution of this camera, 5616 x 3744 pixels, allows an entire object to be captured at a fairly high resolution in a single image. Generally the camera is mounted on a studio stand and the filters are changed manually, without changing the focus or position of the camera. Movement of the camera or focus while changing the filters manually could affect the alignment of the images. A filter wheel could be useful to avoid these small shifts, however this increases setup costs and manual changing has been adequate so far. Nine filters are used, producing nine monochrome images for each filter. The transmission curve for the filters can be seen below.

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The app offers you the easiest way to calculate the exposure time to get the most out of your ND-Filter. Use the handy timer to set the perfect exposure time.

hyperspectralvs.multispectralremote sensing ppt

Before you can select a correct depth of field, you must master how to manipulate depth of field. Effectively manipulating DOF depends upon four variables: aperture, focus distance, focal length, and sensor size.

The same camera, lighting and filters can be used for multispectral imaging. MCI will need to incorporate additional steps for the proper acquisition and calibration of images and a software solution for visualization and analysis.

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Multispectralandhyperspectralimaging

I’ll give you a practical example of DOF out in the field. During one of my trips to Oregon, I shot two photographs in a lovely, open field. One flower in particular called attention to its tiny self with a remarkable burst of color. For the first shot below, I used an aperture of 3.5 (f/3.5). Notice how soft the background appears. Only the flower itself and a few blades of grass are in focus.

Multispectralandhyperspectralremote sensing PDF

Delaney, J. K., E. Walmsley, B. H. Berrie, and C.F. Fletcher. 2005. Multispectral Imaging of Paintings in the Infrared to Detect and Map Blue Pigments. Proceedings of the National Academy of Sciences Scientific Examination of Art: Modern Techniques in Conservation and Analysis Washington, DC March 2003, 120-136.

The next step was to find the right tree for my “point of interest”. I walked up and down the road searching for the best one. But each time, there was something distracting behind the potential tree. A trunk that tilted at an odd angle – calling attention to itself. A broken branch. Too much white trunk behind and not enough golden color. Oftentimes, trees were simply too close to let just one stand out on its own.

In my case with the aspen trees, I really wanted to show off the details on the trunks of the trees. But I also wanted to ensure that the colors were an important part of the photo. And, for anyone who has seen a lot of my photography, you may know that I am almost always looking for a minimalist nature photography composition. So, of course, that was part of my planning as well.

Warda, Jeffrey, Franziska Frey, Dawn Heller, Dan Kushel, Timothy Vitale, and Gawain Weaver. The AIC Guide to Digital Photography and Conservation Documentation. 2nd ed. Washington: American Institute for Conservation of Historic and Artistic Works, 2011. Print.

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With the availability of low cost hyperspectral cameras, hyperspectral imaging is starting to be used as a nondestructive technique that can help with material identification in cultural heritage objects. The complex 3D datasets that are generated through hyperspectral imaging are similar in form, if not in content, to the astrophysical datasets studied at SAO.

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As stated above, hyperspectral imaging is a reflectance imaging spectroscopy technique that involves collecting images with bandwiths of a few nanometers or less. The system used at MCI utilizes a CCD censor and has a spectral sensitivity from 400-1000nm. The camera acquires 128 images between 400nm to 1000nm creating a data cube that can provide reflectance spectra for pixels or areas of interest, as well as images of the area analyzed at a particular wavelength. The reflectance spectra helps researchers, conservators and scientist with material identification.

If your focus distance decreases, your depth of field also decreases if everything else remains the same. One good way to increase your depth of field is to move away from your subject. The subject gets smaller in the frame and has a bigger depth of field. There is a trade-off between the size of your subject and depth of field.

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Multiband, multispectral and hyperspectral imaging can carry a range of definitions depending on the project and application. These techniques presented on this website are defined here, along with reflectance imaging spectroscopy, to clarify the differences between them. Multispectral and hyperspectral imaging are both types of reflectance imaging spectroscopy, which Ricciardi et al. (2013, 13) define as the "collection of images at many different wavelengths to obtain reflectance spectra over a large spatial area." Reflectance refers to the light reflected or scattered by a material relative to the incident light, and reflectance spectra is a curve illustrating the amount of reflectance at each wavelength over a defined spectral range (Fischer and Kakoulli 2006). Ricciardi et al. (2013) define multispectral imaging in the context of reflectance imaging spectroscopy as the acquisition of calibrated images with bandwidths of tens to hundreds of nanometers and hyperspectral as the collection of images with bandwidths of a few nanometers or less. Multiband imaging is similar to these techniques, however it refers to the acquisition of uncalibrated images with bandwidths of 100's nm that are captured using a modified digital SLR camera and bandpass filters. Similar to hyperspectral and multispectral imaging, multiband imaging captures characteristic spectral information about objects, however the uncalibrated image sets cannot produce reflectance spectra.

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Let’s start with the basics. As I already mentioned, aperture impacts a frame’s DOF. So, we will start there. The technical explanation for adjusting aperture settings is fairly simple: the wider the aperture, the narrower your depth of field becomes. Although it looks simple on paper, many students have a difficult time visualizing the concept of depth of field in practice.

Ricciardi, P., J.K. Delaney, M. Facini, and L. Glinsman. 2013. "Use of Imaging Spectroscopy and in situ analytical methods for the characterization of the materials and techniques of 15th century illuminated manuscripts." Journal of the American Institute for Conservation 52(1): 13-29.

Hyperspectralimaging

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To add yet another dimension to this challenge, DOF is often an artistic choice. This fact can often be particularly challenging to beginner nature photographers.

There is nothing more remarkable to me than the power of nature. It is both cataclysmic and subtle. Slow and continuous erosion by water and wind can create landscapes every bit as astonishing as those shaped by catastrophic events – and minuscule details can be as breathtaking as grand vistas that stretch from one horizon to the other. Nature is incredibly diverse. Burning desert sands and mossy riverbanks… Brilliant sunbeams and fading alpenglow… Silent snowfall and raging summer storms… Each offers a unique opportunity. I am irresistibly drawn to the challenge of finding my next photograph, and mastering the skills required to capture it effectively. Website | Google+ | Facebook | Twitter | YouTube

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We were in this spot for about 20 minutes, and I have just one image to show for it. But it’s exactly the photo I wanted. As you can see, nature photography composition sometimes leaves aperture as the only element available to manipulate the depth of field in a photo.

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Depth of field (DOF) is defined as the area in your frame where the photo is acceptably sharp. Getting the right amount of sharpness in nature photography can be quite challenging. Most photographers know that aperture impacts DOF, but there are many other interrelated factors that also affect it. Because each of these factors work closely together, it is not always easy to predict their impact.

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Hyperspectral vs multispectralcamera

If you use two different lenses with the same focal point and aperture, the longer lens displays a shallower depth of field. Of course, the composition also displays differently with the narrower field of view on the longer lens.

Each monochrome image records the interaction of light (reflection and absorption) with the material of the textile and pigment at the specific bandwidth of the filter. The variation of the interaction of the light with the different bandwidths can reveal and distinguish materials. Image subtraction with image processing software such as Adobe Photoshop or ImageJ can be used to process images to better reveal some of the pigments used. Image subtraction is a simple, powerful process that can be applied for visualizing the difference or changes between two images (Jain 1986). The pixel values of two images are subtracted resulting in an image that reveals the differences between the pixel values of two images.

Smaller sensors have a wider DOF if you keep the field of view the same. This is a tricky concept to understand. Sensor size changes your field of view for any given focal length and aperture. Because of this, shooting the same scene with a smaller sensor requires you to step away from the subject to keep the field of view the same. This translates into a larger DOF.

The first step is to consider the most important element in your image. What are you trying to show? Is it the sweeping landscape? The beautiful mountainside? Or is the most important element of the image the colors themselves?

In this case, I prefer a wider aperture and the resulting narrow depth of field. The soft background leaves the image feeling soft and dreamy. It also serves to eliminate a lot of distracting elements.

The Smithsonian Astrophysical Observatory (SAO) and MCI received a 2013 Smithsonian Grand Challenge Level One Grant from the Consortium for Unlocking the Mysteries of the Universe to fund Adapting SAOImage DS9 for General Purpose Hyperspectral Imaging. Members of SAO have developed extensive expertise in the visualization and analysis of complex astrophysical datasets. SAOImage DS9 is a software application developed at SAO specifically for this task and is widely used world wide by the astrophysical community. In particular, SAOImage DS9 has enhanced support for the visualization of large complex 3D datasets without the need for advanced or specialized computer hardware.

Now look at the second photo (above). I took this shot at f/16. With a much narrower aperture, the result is obvious. The depth of field is much wider. In this image, you can far more leaves and grass in the background as well as a bit of brown. For me, all of these details are distractions that draw your eyes away from my tiny subject – the flower.

Of the four variables listed above, controlling aperture is the most practical method for changing your depth of field in nature photography. Although there are occasions when you will move closer or further away from your subject and when you will change your focal length, but these depend on your location and the subject you are photographing. Sensor size is fixed by the camera you are using. All of this being considered, unless you are using two different camera bodies, aperture remains the most likely and practical method for changing your depth of field.

You may also notice that I’ve lost some of the sharp details of the flower itself. This is part of the trade-off when you are working with a narrow depth of field. I love the effect – but you may wish to choose an aperture between f/3.5 and f/16 to get a little more sharpness on your flower and a little less softness in your background. This is an artistic choice that every nature photographer must make.

Multispectralandhyperspectralremote sensing

Dyer, Joanne, Giovanni Verri, and John Cupitt. "Multispectral Imaging in Reflectance and Photo-induced Luminescence Modes: A User Manual.". The British Museum. The British Musem, Oct. 2013. Web. 25 June 2014.

To fully exploit the information obtained by the hyperspectral imaging camera at MCI requires a sophisticated visualization and analysis software package. The work between SAO and MCI involves investigating the possibility of adapting SAOImage DS9 to support general purpose hyperspectral visualization and analysis. Bill Joye (SAO developer) and E. Keats Webb are working closely to determine the requirements for visualization and analysis, to identify which of these functions already exist within SAOImage DS9, and to determine the effort required to provide MCI (and others with similar needs) the full functionality that is required.

This tree I settled on what just right – but only if I stood in the right place and used the correct focal length. There’s actually a dead trunk just behind this one, but I chose an angle that hides it. I then used a 200mm focal length to create a perfect composition that eliminated all distracting elements.

When we drove past this glen, I knew we were in the right place. The road was high enough as were the bases of the trees. And behind my scene was a vast mountain that blocked the brightness of the sky. Perfect.