 way, the result is a package of evasions that transfigures whatever was nasty, savage, stagnant, or pathological in tribal culture into something estimable on the basis of artistry alone. Popular misconceptions of the Maya as peaceable agrarians remain intact. Museum-goers stroll admiringly from delicately carved femurs to funerary effigies, incised masks, gorgeous ceramics, and headdress ornaments. The elaborate refinements on view conjure a Rousseauean cultural fiction while historical realities shrivel to objets d'art. Suddenly the Stone Age looks good.
Royal Maya tombs were "lavishly furnished with grave goods," we learn. No one mentions that those goods included the kings' slaves, killed for the occasion.
A carved altar is displayed for its acrobat iconography; omitted is recognition of its function as a slaying stone. On altars like this, a sacrificial victim was laid on his back, arms and legs held down, while an executioner carved out the living heart. The corpse was rolled down the temple steps and flayed, its bloody skin worn in dance by a priest. (The son of a modern Maya priest, featured in the catalog as an exemplar of tradition, makes do in a deer skin.) Since rain gods were fond of small things, children were prized oblations, hurled into deep wells still living or with their hearts torn out.
Curatorial tact winks at the dubious particulars of bloodletting and skips ritual murder. Commentary takes refuge in the catch phrase "ritual activity" and concentrates, instead, on the pronunciation of Maya glyphs.
Maya temples were places of worship and prayer "like modern churches, synagogues and mosques," the catalog intones. References to the Sistine Chapel or Sainte-Chapelle in Paris insinuate an equivalence between Christian and Maya habits of piety. Yet radical differences exist between worship of a god who frees man from cosmic necessity, and, say, Xipe, the god of flaying, or Ikal Ahau, who savors raw human flesh.
An exhibition that ignores or denatures these differences tells us nothing worth knowing about history. Or art.
Until September 10 (1000 Fifth Avenue at 82 Street, 212-570-3951).
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Beverly Mutindi Chogo
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Beverly wants to live in a world where Africans have been empowered to be self-reliant, with a mindset that solutions to our problems are within and not without. As co-founder of SophieBot, a sexual reproductive health app that provides credible and verified answers to over 30,000 questions being asked by users aged 15-24 years on sexual and reproductive health issues, she describes her role as “a journey of triumphs and failures, learning and unlearning things, but above all else an exercise in mentorship.” Beverly is currently in her last year at the Jomo Kenyatta of Agriculture and Technology (JKUAT) studying Genomic Science.
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Video not available at this time. Check back later.or likes and dislikes. Whilst some habits may be supportive, others create rigidity and limitations. Holding on tightly to old habits as you are trying to grow can cause barriers to your growth.
The perception of what is possible is limited by what has been, in the past.
To stay in line with what is uplifting us most in our present experience, we must remain open to new possibilities, allowing ourselves to get playful, creative, and even messy or silly sometimes, as we release the habits that no longer serve us and explore something new.
The past months have been all about breaking up routines for me. As my son is away in the USA I have had space to rethink habits that have dominated my life as a working mother for the last 17 years. And so I have re-looked at my nutrition, my sport, and my morning routine, asking myself if this is still in line with how I want to live now and in the future. And it got me to thinking that habits should be reviewed annually, together with without our goals, because perhaps it is an old habit that stops us from achieving that new goal we have set?
This is where mindfulness practices such as meditation and art-making can support us in releasing old habits and recognizing and embracing new habits.Wavefront-coded imaging is a new technique in imaging systems that uses signal processing as an integral part of image capture. In additional, wavefront-coded imaging uses custom lenses that are optimized specifically for each application. This combination of an application-specific lens and signal processing can deliver performance that is impossible with traditional imaging systems.
Wavefront-coded imaging can be explained by drawing an analogy to communication systems, where signals are encoded for transmission across a channel and decoded upon reception to extract the relevant information. The wavefront-coded optical element codes the optical wavefront from the scene in such a manner that the relevant information about the scene is retained at the focal plane. The sensor in a wavefront-coded system is a typical CCD or CMOS sensor, and it digitizes the coded image at the focal plane. The signal processing decodes the coded image and delivers an image with minimum artifacts and defocus error.
The wavefront-coded image prior to processing (“coded image”) resembles a blurred image of the scene except that the blur is independent of object distance (see Fig. 1). Objects in the foreground and background appear equally blurred, which is contrary to a traditional imaging system.
Typically imaging systems are focused at a nominal object distance from the lens. Objects that are far removed from this nominal distance are blurred and have defocus error. Conversely, objects in and around the nominal distance are imaged in sharp focus. Depth of field (DOF) is the distance between the nearest and furthest points where objects appear in acceptably sharp focus.
A large DOF is desirable because it reduces the need for actively focusing the lens. The alternative to a large DOF is autofocusing, where the lens is mechanically focused for each frame. Autofocusing adds considerable mechanical complexity and wear-and-tear issues that lead to higher cost of ownership. On the production floor, where throughput is critical, the time taken to refocus the lens translates to reduced system throughput. In other scenarios, such as web-based-production, a shallow DOF imposes tight tolerances on the material handling equipment. Such tolerances lead to higher capital costs and longer down time to keep the system tuned within the specification.
The DOF of an imaging system varies with the entrance pupil diameter, the focal length, and the object distance. In the case of a simple lens, the entrance pupil is the same as the lens aperture. With the focal length and object distance held constant, reducing the lens aperture increases the DOF. However, reducing the aperture also leads to lower light captured from the scene and lower resolution.
In addition to the DOF, the focal length and the aperture also determine the light gathering capacity of the lens, which is usually denoted by thef-number (f/#). The f/# is the focal length of the lens divided by its entrance pupil diameter. Lenses with a large entrance pupil compared to their focal length (small f /#) capture more light from the scene compared to lenses with a smaller entrance pupil (large f /#). Each increase in the f/#, which goes as f /1, f /1.4, f/2, f /2.8, f /4, f /5.6, f /8..., reduces the light-gathering capacity by 50%. Thus, doubling the DOF by going up two f-stops implies reducing the light captured to 25% of the original amount of light.
Reduction in the light-gathering capacity of the lens has other implications. The acquired images may suffer from lower contrast and lower signal-to-noise ratio (S/N). The illumination system may need to double its power with each increase inf/#. The camera may be required to operate at a longer exposure time to capture more light. Reduced contrast can lead to poor detection. Increasing the illumination leads to power, heat, and source lifetime issues. Longer exposure time can lead to motion blur that offset the gains from the increased DOF.
In addition to the light-capture capacity, the lens aperture also has implications for resolution. The maximum spatial frequency of the lens is directly related to the aperture size. Reducing the aperture by half halves the optical resolution. This trade-off is often not considered by system designers since imaging systems tend to be undersampled and the cut-off spatial frequency is determined by the sensor’s pixel pitch, rather than the lens aperture. However, atf/16 or higher, the diffraction limit could be the limiting factor and have adverse effects on the application.
Wavefront-coded imaging can deliver systems that operate with large apertures (lowf/#) but offer the DOF of a reduced aperture system. Typically wavefront-coded systems can increase the DOF by a factor of three to five times that of a traditional system (non-wavefront-coded) while maintaining the equivalent f/#. For example, the lens can be operated at f/2 but deliver the DOF of a lens operated at f/8.
Wavefront-coded imaging is best explained in the frequency domain using the modulation transfer function (MTF), which is the Fourier transform of the system point-spread function (or impulse response). The MTF plots contrast as a function of spatial frequency.