How to communicate an erratic process in terms of an image ? The Iliadic greek were pirates of the Mediterranean with fast vessels, invading mainland from the seas, enslaving people, robbing stocks and much more.
The writing down of the Ilias was between 678 and 662 B.C., a time of Assyrian dominance and cultural superiority.
With three different Nautilus shells I bought last September on Crete I did this composition on my big X-ray sensor with 35cm x 43 cm and 170µm per pixel resolution. Two energy levels were necessary to get a high resolution image of the core of the Nautilus shells.
To overcome the look-and-feel of a medical X-ray it is a logical idea to invert the light. Black becomes white and vice versa. White means shining through of X-rays, black means opacity. It’s like a dream !
How to prepare a X-ray session ? What flowers suit to a Nautilus shell ? Where does color come in ?
I went to my gorgeous florist to have a look what offer she can make during wintertime. My phantasy were spinning around something ethereal or unrealistic. I bought some flowers with respect to their shape.
The Anthuria caught my eye immediately. The Tulip was still closed and got more and more yellow within hours.
All these compositions shown here were made with dual energy X-ray. The lowest energy of the tube is 40kV, which yields with 4 mAs a quite good insight of flowers. For the center of the Nautilus shell, 70kV and 2.5 mAs is more appropriate.
My first composition was a Nautilus taking off a bouquet of flowers. This reminded me of Renaissance engravings full of symbols. I do not feel depressed. The representation as a X-ray positive jsut shows the bouquet.
A more grounded composition is the second with a Nautilus shell moving towards the roots of my bouquet. Hopefully, the plants will survive. The positive representation always needs some extra editing. By just inverting the Blacks and the Whites the Nautilus would be too dark. Our reception cannot be just inverted and feels alright.
With the look-and-feel of old engravings in mind the third composition ist between surreal and a still. It took me some time to mask out the flaws of an original X-ray to get a true black background. Masking can be done iteratively and easily combined with Photoshop. („That’s what Photoshop is made for !“).
Some colorizing was done to overcome missing photographic shots. There was simply no time in my X-ray unit to do both at a time.
My fourth composition is called „The Argonauts“. The Nautilus shell serves as Argo, the legendary fast ship, with its crew, called Argonauts. The colored version is more convenient for our eyes. As before the X-ray positive looks more ethereal.
X-rays were initially used for research in atomic physics and medical diagnostics and therapy. Their ability to reveal structures inside an object even with an opaque surface was the driving feature of scientific and technical development of X-rays. Nowadays, beside its proven medical usefulness, X-rays are used to examine technical structures and there are telescopes to map X-rays from our Galaxy and the universe. Every radiological technician who starts in its profession learns to do X-rays of common structures like flowers, animals or teddy bears.
In the digital era, X-ray images are obtained using sensors, while film was used historically. The sensors in the medical radiological field have dimensions such as 24cm x 30cm or 43cm x 43cm. The corresponding spatial resolution for these sensors is between 70µm and 140µm. A typical high-end camera used by a professional or advanced amateur photographer might have a pixel resolution between 4 and 8 µm. Therefore, photographers might well wonder if there is any precise imaging possible with such pixel size. Let’s look at this a little more closely.
X-rays, like visible light, can be characterized by their energy or wavelength. Shorter wavelengths correspond to higher energy. The capability to penetrate an opaque structure increases with energy. If you think of a photon as a particle, smaller particles with higher energies penetrate an object more easily. An overview of this relationship is given in the table shown here:
To make this more clear, here is a series of X-Ray images with increasing energy. The first image was obtained with 40 kV which corresponds to a wavelength of 0.031nm. Our eyes are only able to see wavelengths between 400nm (blue) and 750 nm (red). Therefore, photons with a wavelength at 40 kV cannot be seen with the naked eye. The peripheral parts of the Nautilus shell are clearly depicted. A photographer would classify the circle at the center of the shell as „blown out“. In fact, they are not blown out. The radiation is not able to resolve the structure, because the wavelength of the X-rays is too long in this case to penetrate the shell.
Let’s go to shorter wavelengths (implying higher energies). Using 50 kV or a wavelength of 0.024nm gives more structure to the central parts. The photographic impression of a „blown out“ center is reduced. However, looking at the peripheral parts of the Nautilus there is a loss of intensity and a more grayish impression. It is conceivable that this might be regarded as an overall acceptable but subtle effect.
To take this further, we can go up to 60 kV or down to 0.0207nm. The center is now close to perfectly „exposed“ with some detail apparent, although some smaller structures are still not resolved. The intensity loss at the peripheral parts increases and is now pronounced. A photographer would clearly regard the periphery as „underexposed“.
The last example of this direction of higher energy and shorter wavelengths is 70 kV or a wavelength of 0.0177nm. The photons wavelength is now 57% compared to 40 kV. You may think of this as „smaller“ photons. The result is a clearly depicted core with a complete loss of peripheral structure. A photographer would have every reason to be worried about „underexposure“ and loss of detail everywhere but the center.
What we’ve seen here is that the capability of X-rays to penetrate an object and to go through an object is dependent on energy levels. With shorter wavelengths X-rays go through an object without disturbance but our sensor is „blown out“ at the peripheral parts of the Nautilus shell. Using 70 kV the central parts are much better resolved, but the periphery is too dark. The energy to use for any X-ray image therefore often depends on the primary goal of which portion of the subject is most important to capture.
In a certain sense, the compositing of images with different energies into one image can be compared to the HDR process of photography in the field of visible light. Whereby in visible light the intensity plays the essential role and not the light energy, which determines the color. When X-raying an object that requires different energy levels for accurate representation, I would therefore also speak of a High Dynamic Range image.
If combined, the four exposures shown provide a beautiful, nearly weightless image:
You always need some time to find out the best exposure values for a photo. Same idea holds in X-Ray imaging.
Today I did an x-ray series with my biggest Nautilus shell on a conventional radiography sensor, not a film. Starting from the lowest possible value 40kV an increment of 10 kV up to 70 kV can be seen in the images:
Black regions in the image a transparent, white are opaque. The center of the Nautilus has a loss of structure.
With 50 kV the structure in the center of the Nautilus is better depicted wheras the edge gets more transparent:
Same effect for the center and the edge can be seen with 60 kV:
With 70 kV it’s an exaggeration for the edge and best depiction for the center:
Higher kV means more transparency for denser structures but a loss of structure in transparent areas.
At fixed energy, X-Ray imaging behaves like a shadow related to visible light. When photographing, there is not chance to look through an opaque object. With higher energies, x-rays go through opaque objects and can be collected on a sensor.
Composing the images obtained at different energies is an X-Ray HDR image:
The representation of an X-Ray with white on black is a reminiscence of the film era. Radiologists just looked at the negatives ! Inverting black and white shows the positive image, like a print. Here I show the same image as positive, but rotated and flipped horizontally. Look how ethereal it appears now:
Today I put some tests on my cretean purchases from last September to evaluate their potential of being subject to fusion imaging. I bought three Nautilus shells and two sea snails, holding them in the store against the sun to check their transparency. My untidy studio accommodated these precious stones under quite a bunch of something.
The best representation is with a black background, i.e. with inverted L-channel in Lab colors. With a black background a soft shining light appears in the objects.
This snail has a shape a triangle and resembles a bear claw or an Apollo capsule in the late Sixties. The translucency is very little.
The following snail has a classic shape. With the black background it resembles a galaxy in outer space.
My first attempt with the Nautilus shells led me to a copper-like color representation with a single shot image. Lab colors is the key to this color and light distribution. Very attractive is the fact of two shells turning right and one left. Why did I wait so long to make this image ? Why do we miss important opportunities ?
Thanks to my hard-working father-in-law we enjoy every year phantastic cookies. This year I had to cope with different archiving modalities in mammography due to quality management. This image was an idea to enjoy Christmas in advance with a composition of a Poinsettia. Simple structurizing effects render this image into a sort of cookie smelling painting.
Are you already high-brow ? You don’t want physics, because you didn’t like it at school ? Then take a look at a well understandable FAQ-sheet for x-rays of flowers given by Harold Davis. The doctor advices you to stop reading here !
Those who like some more background may read the following paragraphs.
Our eyes are sensitive to visible light. The wavelengths of visible light range from 400nm to 750 nm. Digital sensors for photography are modified in their sensitivity to gain a pleasing image for human eyes. E.g. we like green tones. A digital sensor for photography can be modified in its sensitivity within the range of visible light and over a wider range of wavelengths than visible light. The energy of visible light ranges between 1.6 eV (750nm) and 3.2 eV (400nm). Typical spatial resolutions of photographic sensors in the consumer section are between 4µm and 8µm.
A digital x-ray sensor works with spatial resolutions between approximately 70µm and 140µm. Using a medical x-ray machine the available energy levels of x-rays depend on the purpose of a human examination. Energy levels of mammography systems vary between approximately 20 keV and 45 keV, depending on manufacturer. Energy levels of conventional x-rays for bones or chest vary between approximately 80 keV and 125 keV. The corresponding wavelengths are under these conditions 0.06nm (20 keV) down to 0.01 nm (125keV).
As you may know, visible light and x-rays are part of the electromagnetic spectrum. Visible light and x-ray differ in their energy. Higher energy of a radiation means higher frequency and shorter wavelengths. Our eyes don’t see other light than visible light. X-rays are a special light then, not to be seen with our eyes – but with a digital sensor.
A substantial property of x-rays is their ability to run through objects with mainly no interaction. The x-ray sensor „sees“ only a small percentage of less radiation coming from the x-ray source when an object is placed near the sensor.
The left hand image appears normal to your eyes when thinking of an x-ray. Before the digital era, radiologists were using films, an analog medium to produce an x-ray. As x-rays run through an object with mainly no interaction, the dark parts of the left image were fully exposed to radiation. A dark part in an x-ray image therefore was called transparent by radiologists. The parts with lighter grey or white in it were called „opaque“ or „dense“ or „attenuated“ areas. The brighter parts result from the attenuation of radiation by an object. As a matter of convenience, digital x-ray images are shown like the left image. You see already details of the inner structure of our flower, a Bird of Paradise.
The right hand image is an inverted grey scale image. Black turns into white, 50% grey stays unaffected and white turns into black. A 75% grey turns into a 25% white. In every photo editor that’s just a simple and easy action to do. The inverted image is more pleasant to the perceptive habits of our eyes. To our experience, the inverted image is preferable for fusion imaging.
Explanation of the idea
Fusion imaging is a child of the digital era of mapping structures. Before image fusion was used in diagnostic radiology, astronomers used it to extract new insights from our universe. Fusion imaging of flowers can be beautiful. And, maybe, it’s a starting point for research in new fields.
The use of photography was initially, after its invention in the 40s of the 19th century, nothing more than a gadget. Only by astronomers, that used used photography for detection of asteroids, photography became a serious matter. By comparison („blinking“) of photographies astronomers discovered mobile objects within a field of fixed stars. In Heidelberg, Max Wolf (1863 – 1932) has been a pioneer of astrophotography.
Imaging of flowers is nothing new. But in the digital era of photography, the mapping possibilities changed fundamentally. It became possible to create the illusion of transparency or translucency by using a set of HDR images at the HighKey side of the exposures. The procedure was introduced by Harold Davis.
X-rays were initially used for medical diagnostics and therapy. Their ability to reveal structures inside an object with an opaque surface was the driving feature of technical development in this field. Nowadays x-rays are used to examin technical structures and there are telescopes to map x-rays from our Galaxy. Every technician who started in its profession learned to do x-rays of interesting structures like flowers, animals or teddy bears. X-ray images of flowers are nothing new.
Transparent looking flowers and transparent looking x-rays of the same flowers are each already for itself appealing to our eye and mind. By combining two digital images of the same structure in visible light and x-ray there is something new to happen. We name this combined procedure „fusion imaging“ and the result of a combination a „fusion image“.
How it works in a nutshell