209

There is a tool called dcraw which reads various RAW file types and extracts pixel data from them — it's actually the original code at the very bottom of a lot of open source and even commercial RAW conversion software. I have a RAW file from my camera, and I've used dcraw in a mode which tells it to create an image using literal, unscaled 16-bit values from ...


44

I will only answer the first question: What are frequencies in images? Fourier Transform is a mathematical technique where the same image information is represented not for each pixel separately but rather for each frequency. Think about it this way. The sea has waves some of which are very slow moving (like tides), others are medium in size and still some ...


24

Luna 3 did something as complicated as you thought: It took photos on a film, processed it in a kind of onboard minilab, and then scanned and radioed it back home in analog way not unlike an old fax. Funniest part was that Soviets didn't have the technology of radiation-hardened film, but Americans did. They used it against Soviets in high-altitude spy ...


21

I think the main problem is one of dynamic range, your algorithm is probably right but you're working on the wrong type of data. A point light source that would otherwise clip and go pure white gets spread over a larger area by a defocussed lens, so that it forms a disc that isn't as bright and therefore doesn't clip. That's why you get those nice circles ...


20

To reduce the processing time for long exposures, you want to turn off Long Exposure Noise Reduction. However, you may not want to give up the benefit of LENR. Long Exposure Noise Reduction (LENR) is Canon's nomenclature for in-camera dark frame subtraction. When you take a photo the camera will expose the image normally and then use the same settings to ...


19

Amongst the myriad online pages documenting the Viking series, here's one which states clearly The Viking Lander camera design was very different from vidicon framing or CCD array cameras. The lander camera was a facsimile camera with a single, stationary photosensor array (PSA), and azimuth and elevation scanning mechanisms. A lander image was ...


19

It's been done in X-rays. The TimePix is a 256x256 detector. It has three operating modes: the usual "total energy in this pixel since we started integrating"; Time-over-Threshold (TOT): the detected pulse height is recorded in the pixel counter in the TOT mode; and Time-of-Arrival (TOA): the TOA mode measures time between trigger and arrival of the ...


18

You are missing some obvious problems with this idea. You want to "continously" capture the light data, but that's already being done. Apparently you mean to have a series of images available after the exposure, each exposed from the start to times advancing withing the whole exposure. The later images would have more detail in shadow areas, but might ...


15

I don't know if it's the easiest but this works pretty well for my needs: $ align_image_stack -a aligned -C *.jpg 'align_image_stack' utility is part of hugin, and under Debian/Ubuntu (and other derivatives probably) you acquire it by installing 'hugin-tools' package. In the command above: '-a aligned' sets prefix of the name of output images to 'aligned' ...


14

No, you can not and it does not make sense to do so, since there is no ubiquitous definition of the JPEG compression level. The actual result when saving a JPEG with compression level 60 in one software can differ significantly from what another software produces when set to level 60. If you use ImageMagick as suggested by Rolazaro Azeveires, it will indeed ...


13

It's a really really big grid of numbers. Everything else is processing.


12

First of all, in optics, only light adds up and darkness does not. Make sure that your algorithm does not bleed dark pixels outwards their original location. Resulting pixels should rather resemble maximum of nearby source pixels than average. Or, to be even more exact, you'd be summing up logarithms of affecting source pixels. Another possible cause why ...


12

Support for reading HEIF was added to ImageMagick 7.0.7-22, you have to install it with --with-libheif flag. e.g. on macOS with Homebrew: brew install imagemagick --with-libheif. If you have previously installed imagemagick with Homebrew, you need to uninstall it by brew uninstall imagemagick first. One other option to convert HEIF → JPG on macOS is by ...


11

Have a DOG sniff out blur in the photos. If you're going to be penalizing for digitally enlarged photos, you might as well penalize for out-of-focus photos too. The blurred edges and details in both cause the same bad experience for viewers, regardless of whether it is caused by a small original or poor focus. What you want to do is detect blur, which is an ...


11

Color photography is indeed based on the tri-color theory. The world saw the first color picture in 1861 made using red, green, and blue filters by James Clark Maxwell. Today’s color photography is based on his method. In 1891, Gabriel Lippmann demonstrated full color images using a single sheet of black & white film, no filters, no colored dye or ...


11

You suggest "Or every time a photon hits a pixel on the sensor give it a timestamp" — this would be a huge amount of data. A quick search suggests that each pixel — or sensel — in a digital camera saturates at somewhere between 20,000 and 100,000 photons. Let's say that we're happy with a 12 megapixel camera and are okay with the lower side of sensitivity ...


9

I will try to explain with the simplest math terms possible. If you want to skip the math, jump to part II, if you want to get the short answer skip to Part III Part I Frequency of a signal means the number of occurrences of a repeating event per unit of time. So if the unit of time is seconds then frequency is measured with Herz: 1Hz = 1/s. So a signal ...


9

There doesn't appear to be any moire in the image itself. What you are seeing are scaling errors when the image is resized by a particular application for display on a particular size screen or print. To solve this you can create, optimize, and export different resolutions of the image for different display environments. For instance the display on a ...


9

For photographic images and when a not too high level of compression is used, the loss of quality in the JPEG format is negligible and invisible. You'll pretty much only be able to notice it by directly comparing individual pixels around sharp edges or in very smooth color gradients. This is why JPEG is so popular. If it always resulted in noticeable loss ...


9

The 14 bit depth is the limit of the physical sensors capabilities, it isn't just that the engineers decided to throw away useful data. An increasing number of bits available in a sensor reflects an increasingly larger complexity of circuitry and precision needed to resolve those progressively finer and finer details. Complexity and precision don't come ...


9

This is actually really simple: your image is shown in color by Darktable because it renders the preview from the RAW file in order to show it to you — including demosaicing. (Or, depending on settings, it may initially show you a low-quality JPEG preview actually embedded in the RAW file by the camera.) This is why I find the whole "RAW isn't an image; it'...


9

I'm not sure how much they can really be rescued - there's one heck of a lot of blue in there & very little of anything else. Applying a Levels Layer & pushing the mid-point of each colour by eye to where it's at its strongest will restore it a little, but it doesn't look very natural. Quick attempt, each colour set in the same way, just by eye &...


9

While darktable is an increasingly powerful piece of software, one of its rough edges is the fact that it doesn't try very hard to produce a good default "vanilla" rendering of the RAW files from the vast array of cameras that produce such files (understandable, being an open-source project with limited volunteer resources). By default, it applies a "base ...


8

You can, sort of. ImageMagicks' identify command can show a estiamte identify -verbose image.jpeg will produce (a lot of) information about the image. One of the lines will be something like: Quality: 84 If that command shows too much, and you only need the quality, you may pipe it with grep: identify -verbose image.jpeg | grep Quality (Stolen and ...


8

It's roughly true that light sources with the same color temperature have the same appearance. In fact, matching light sources in this way is exactly the reason we use the Kelvin WB scale in photography. However, there are three big caveats. First, there's also a magenta-green axis Human perception of color is complicated. White balance as measured in ...


7

To fix this, you need to decompose your image to RGB channels separately. R and G channels are vertically shifted from B channel by 5 pixels each. You need to align these channels vertically. For example I have shifted red channel 10 pixels and green channel 5 pixels from the blue channel. Here is the result with comparison : Shifted one Corrected one ...


7

I think this question can have better answers in another site, like Security StackExchange. And there you'll get answers that, in the end, will tell you the following: it's impossible. If you really don't want anyone to copy your pictures, you can't let that person touch it. Then the long answer will be the following: Security is a matter of trade-off: you ...


7

A perceptual uniform color space ensures that the difference between two colors (as perceived by the human eye). It is proportional to the Euclidian distance within the given color space. You may think that the lightness component of the HSL color system or the value component of HSV will solve this problem, It's wrong. The L component of the HSL and the ...


7

You're looking at JPEG artifacts. The JPEG compression scheme divides an image up into 8x8 pixel blocks and rebuilds each block using a collection of 2D waves as building blocks: You can faithfully recreate any image by adding together a combination of wave images with the correct brightnesses. However JPEG is a lossy compression algorithm and so it throws ...


7

Is this already being done? Sure. The Hubble Space Telescope senses the near IR, visible, and near UV spectrum. Any images you see from Hubble that contain information outside of the visible spectrum are false color images. Similarly, images from Chandra, which observes the X-ray spectrum, can only be visualized by mapping its "tones" to the visible light ...


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