srijeda, 26.10.2011.


Video Low Pass Filter. Bypass School Filter Proxy.

Video Low Pass Filter

video low pass filter

    pass filter
  • A band-pass filter is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range. An example of an analogue electronic band-pass filter is an RLC circuit (a resistor–inductor–capacitor circuit).

  • The system of recording, reproducing, or broadcasting moving visual images on or from videotape

  • the visible part of a television transmission; "they could still receive the sound but the picture was gone"

  • A videocassette

  • video recording: a recording of both the visual and audible components (especially one containing a recording of a movie or television program)

  • (computer science) the appearance of text and graphics on a video display

  • A movie or other piece of material recorded on videotape

  • A particularly bad or difficult moment

  • in a low position; near the ground; "the branches hung low"

  • less than normal in degree or intensity or amount; "low prices"; "the reservoir is low"

  • A low point, level or figure

  • an air mass of lower pressure; often brings precipitation; "a low moved in over night bringing sleet and snow"

  • A state of depression or low spirits

Oldtown Alexandria Waterfront V.A.: dawn

Oldtown Alexandria Waterfront V.A.: dawn

A200/Tamron 18-250 Hoya MCUV filter, ISO200 > dcraw > Gimp with gradient blends & usm]

This was my original "blend". I started by brightening the center +80 and the contrast +75, the part away from center by about +40/+30 & blending with a bidirectional gradient in the middle at about 70% opacity. It came out slightly dark on the right in the middle yet with insufficient contrast away from center... would be very-nice to be able to adjust the two layers and the mask independently and then see a combined version of them in real-time...

And to run a split mask in the middle and reduce the contrast on the right, but after a few attempts at that I gave up as it didn't appear to be worth the effort. Like I said it would be better to see these things before blending rather than after, I can only spend so much time & effort blending two layers on one image for Flickr. Just imagine doing this for an entire video. Literally I was just thinking of writing a 2D low-pass filter for this. Anyway on the bright layer you want to get the contrast in the ballpark, a little low and get the brightness a little high because the blend is going to darken and increase the contrast of the light parts and of course adding more contrast after the blend will make them that much darker and blow-out the highlights & shadows that much more. But the point is that with insufficient contrast the midtones will look pasty and gray and the whole shot looks fake. Obviously that can be overdone to the point where it is overcontrasty and fake, as well. So it's a balance.

Try starting with a linear shot, a raw conversion with no contrast added and the gamma set to 1 ;)

Or try it with two different exposures of the same shot, say one generated with H0W and H7W (with dcraw) and then use a threshold mask and an amorphous gradient blend ;)

This is begging to be done with a "smart" filter, really. But it's why I think the best approach is to just shoot it to expose the highlights properly and then rescue the shadows with a gradient blend, not use a complicated HDR tool and multiple exposures. If it's shot so that the highlights are slightly blown-out but the shadows are better-exposed, and then the shadows are rescued with H7W in dcraw (or the equivalent in your favorite RC) and you try to blend an H0/7W exposure set, then the shot will be slower and less stable. Plus that's a fine line to walk while you're in the field. It's easy to look at the LCD and see if the sky is blown-out, if not all the highlights. That's where I would start, maybe minus half a stop or so, as there will be saturated sections that are not "highlights", like in the above where the sky is saturated red in places. Pushing those will change the color entirely. Oversaturation is another reason why I don't like to shoot to the right even if the camera is noisy in the shadows, and you shouldn't need a meter to tell you what is happening to the highly-saturated parts of the scene if the scene has over 3 stops of DR and the overall exposure is near 0eV according to the camera meter. It is all a balance between the advantages of a certain technique and its negative consequences, in this case you have to balance blowing-out the highlights and getting a flat, dull result with getting noisy shadows and midtones and a shot that is full of crud. So this is one more reason to bracket even if I'm going to end-up throwing-away a third of the shots right there and another 3rd or more once I get home. And obviously if more than one exposure is used and it's not perfectly-aligned, then the edges will get softened by the blending process. So I always work from just one exposure and now I clone it to different layers, push them around, add contrast and blend. You can go from there to doing selective editing on each layer.

The problem of course is the idea of doing all this editing on thousands of shots, even if it can all be done fairly-easily by hand, which in general is far from the case. It simply is not easy to automate vignetting, CA & geometry-correction to the point where it is well-optimized for each shot. Not to mention if you don't hold the camera properly or crop or rotate the shots before processing, not to mention correcting the lighting and doing NR if you want to go that far. It *is* however easy to rip-off a half-a dozen thousand shots with average post-processing especially if you're happy just shooting jpegs. And in the long run, guess which really matters the most: excellent IQ on a handful of shots or good average performance over years of use. Especially when, let's face it: "excellent", for digital photography, means "a decent representation of what we would see if we were there". You're just not going to match, much less "beat", a view of the real thing with a camera, much less a digital camera. If you're lucky it'll be "decent". Sometimes even "impressive&qu

20110815 iPhone 001-TouchRetouch-GeniusScan-FilterstormPro-PhotoFxUltra

20110815 iPhone 001-TouchRetouch-GeniusScan-FilterstormPro-PhotoFxUltra

(Note: Various features are labelled with rectangles and notes if you pass the cursor/mouse over the photo)

Not a photo of Star Wars inter-galactic lightsabers, but a test long exposure night scene using a custom version of the Slow Shutter Cam app on an iPhone4. Looking northeast across Lake Burley Griffin. A cloudy night with a full moon in a city location with lots of background light, so much of the desired star trail detail in the sky has been lost. Still, it was a success in terms of a test of the long exposure. This app effectively stacks video frames, keeping the brightest pixel between the current stack and the new frame. A spring-loaded mount for the iPhone 4, obtained from Photojojo, was used to mount the camera onto a standard camera tripod.

The photo features a moon trail, partly obscured when clouds intervened. Various aircraft light trails were captured - the multiple trails towards the lower left relate to aircraft climbing out of Canberra Airport (across Lake Burley Griffin, behind the building), and some faint NE trails for aircraft at high altitude passing overhead en route from Sydney to Melbourne. The bright NW trail is from Jupiter, whilst the lighter trails are from various bright stars. The bright trails along the lower left edge are from vehicles, including some blue and red lights mounted on top of emergency vehicles.

Barton, ACT, Australia.

The photo was taken on an iPhone4 using the Slow Shutter Cam app in Light Trail mode (and Bulb exposure time length) - my thanks to Cogitap Software for their excellent customer service, willingness to provide help, and for making a custom version of the app available that included the feature that I had requested. The exposure length was approximately 12 hours! Some small spots were attenuated using TouchRetouch. A trapezoidal crop was applied using Genius Scan. Noise reduction was applied using Perfectly Clear. Some local tone mapping was applied using DynaLight HD. A further crop and some minor lighting adjustments were made using Filterstorm Pro. A blue (upper) black (lower) dual gradient filter was applied with Photo Fx Ultra.

I have found various iOS apps useful in this pursuit, notably FlightBoard (listing aircraft arrival and departure times for any airport), Pocket Universe (showing the stars, planets and satellites that will be visible in the sky, including a neat animated time lapse movie option), and Skyview (which has a Virtual Reality feature that allows you to point an iPhone camera towards an object in the sky and the app will tell you the name of the object).

video low pass filter

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