5 votes

How does the HDR in compact cameras?

I am a user of compact cameras, and I'm intrigued with the option that now they bring many models of cameras to improve the dynamic range -HDR-some years Ago I read that the HDR function to take a number of consecutive shots and then made a single image by saving the great defect of the small sensors of a lack of information in areas under-or overexposed. If when you began using this technique in digital photography, few cameras that had to be implemented this function, it now seems that even the most simple models have it. I've been doing some tests and I notice that between images taken with or without HDR, because in the latter the darker areas leave something more overexposed, and inthe bright areas do not appreciate changes. I get the feeling that it is simply an image with a curve modified, but that has little to do with the technique that I write at the beginning. If you know anything about this technique and how it works in the cameras we buy -low ranges, averages, or high-

5voto

Anon User Points 0
**Dada00**! Very interesting your question. What is certain is that the answer that I can give you is more an intuition reasoned that a proven fact, since researching I have not found any technical document that explains it in detail. I will rely on the theory of signal processing (deformation professional to be an Engineer at Teleco :-P) to lay the groundwork and then get to the conclusion. As well comment the **HDR** aims **to increase the dynamic range** of the sensors of digital cameras, one of the horses of battle of the current sensors, and requires a post-processing of the images. As you know, these **sensors do not provide a linear response** in all the range of lights that make up a decision on the amount of information captured, as it is much **more sensitive in areas of high lights of the histogram in the area of low-beam headlights**. This is the explanation of techniques such as the "derecheo histogram" posed by authors such as Mellado, although its application is for very specific cases. You can find it as **ETTR (authored exposing To The Right)** and read about it [here](http://www.dpreview.com/articles/6641165460/ettr-exposed). The digital sensor is composed by fotocaptadores that ** * * assign electric values to the light intensity detected**, values that are limited by the **NOISE** in areas of shadow (when the sensor is not able to distinguish between the level of signal produced by the sensor itself and a valid data actual light intensity) and for the **SATURATION** in areas of high lights (the sensor receives too much light and is saturated, not being able to distinguish more levels of light). When this happens we will have a "**Black-bound**" in the shadow areas (we will not be able to retrieve information from nuances) and a **"pure white**" in areas of high lights. Therefore, the **dynamic range** is determined physically by the limitations of the sensor, the sensor being so much better the greatest differences to be able to pick between lights and shadows before you reach the conditions of NOISE and SATURATION. The dynamic Range is technically termed **Exposure Latitude**, if you would like to investigate more in depth. That said, we should be aware of the next step, that is to say, **what volume of information we are working**. If your camera does not provide us with images **RAW** and, therefore, we do not have all of the information on crude oil that is able to capture, we start to have a smaller margin of manoeuvre. Many of the compact cameras work directly in **JPG**, you are compressing the information that comes out of the sensor, losing by the way an important part of the information. This is an important consideration, before you enter even in the own processing **HDR**, because you're going to lay the groundwork on how it will be processed later in the camera. At this point we can already analyse the functioning of the **HDR mode** in the different chambers, being aware of the three major aspects that are always going to occur: - **Capture at least two images with exposures for shadows and lights** - **Alignment of the images (not all cameras, some require yes or yes on a tripod)** - **Processing algorithms to generate the final image** All the cameras that I have handled with **HDR mode** built-in, according to the instructions of their manuals, go through this process. Where yes I found a difference is in capturing images that will make up the **HDR**, being the most common in **compact range low** that the catches are made in **JPG** not **RAW**, generating the final image also in JPG and, normally, without the possibility to recover the shots used to generate the **HDR**. However, **cameras high range** as the Canon EOS 6D or 5D mk III, mode **HDR** made 3 catches in **RAW** which then combines and aligns it to generate a JPG with the image processed in **HDR**. On this occasion we can download the three source images that make up the **HDR**, even selecting the levels of exposure we want for each of the three shots. Thus, as **to the conclusion that I wanted to get and as an answer to your question, I would say**: - I think the cameras with HDR mode yes performed at least two captures of the scene and then apply a mixing algorithm, and processing them**. Another thing is the quality of the final result that will depend on if they perform the capture in RAW or JPG, the alignment and the "ability" of the built-in algorithms to generate a believable image and really improved. - According to the **physical limitations of the sensor** that we have analyzed in terms of **dynamic range**, **I don't think that we represent an image with a curve as amended** as the curves can act on the information available, but does not solve the problem of the lack of information in the high lights and low Yes, each manufacturer is a world and there I put my hand in fire for none... someone sells you a mode **HDR** and then just force the curve... there I'm not going to get me :-P. Anyway keep in mind that in those images where the dynamic range of the camera is enough to capture the entire scene, you will see few differences with respect to the normal mode. Try it on shots with extreme differences between light and shades to see what result gives you to be able to evaluate the good or bad work that is performed by the camera. However, remember that in order to have control over the **HDR** the ideal is to go to specific software on which to perform the processing as **Photoshop** or **Photomatix**.

1voto

Anon User Points 0
HDR photography is more focused on the post-processing. Is based on take different pictures with different exposure, so that then by means of the software can get the desired effect when combined. There are softwares simple wue allow you to do several tests. The results are surprising; google a bit and you'll see what I mean. Do not forget to assess the response.

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