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"Fun RAW Format"-Basics

1. What is a RAW file?
The RAW file is mainly a file that records the raw information of the digital camera sensor, along with some metadata generated by the camera (metadata, such as IS0 settings, shutter speed, aperture value, white balance, etc.).Different camera manufacturers use various encoding methods to record raw data, compress them in different ways, and even encrypt raw data individually.Therefore, different manufacturers use different file extensions for their raw files, such as Canons.CRW, Minolta.MRW, Nikon.NEF, Olympus.ORF, etc., but the principles and functions provided are similar.
2. Why choose RAW format?
The answer is very simple. Lets take a look at the process of generating JPG in most digital cameras.
After obtaining the raw Raw data from CCD / CMOS, the previously set parameters, such as sRGB or Adobe RGB color space, sharpening value, white balance, contrast, noise reduction, etc., are added moreStrong S-shaped curves (lightening bright parts, darkening dark parts) are transformed (why?This is because CCD / CMOS capture photon energy is based on a linear Gamma (Gamma 1.0), but the human eyes perception of light is non-linear. If this is not done, the image is too dark to see.And people who do not know the reason will definitely not buy a digital camera after reading it. The manufacturer may be closed), get the converted image, and then follow the JPEG quality you set (such as SHQ, HQ, M, S)Compress and get JPG file.
When shooting RAW format, all the settings on the body except ISO, shutter, aperture, focal length, other settings will not work for RAW files, because the above color space, sharpening value, white balance, contrast, contrastAll actions such as noise must be specified when Raw is converted, everything is controlled by you.
To put it in the simplest way, shooting JPG is like taking a picture of yourself, and then take it to the camera manufacturers filmmaker to help you produce the film; while shooting RAW format is to take the picture yourself, develop the negative film, and produce the film yourself.(Look at why Olympus Studio translated the English version of "Raw Development" into the Chinese version of "Raw Development".)
Maybe many people scoff at the post-processing (or PS), and think that the head behind the camera is the most important when shooting in the early stage.Yes, I agree with this very much.However, since there was the spirit of taking photography seriously in the early stage, why cant we use this attitude in post-production?We used to complain that the film we made was spoiled by the filmmaker in the print shop, so we turned to film flipping, which gave us a greater portion of control.Now when it comes to digital, you can give yourself full control from beginning to end, why should you keep it thousands of miles away?Moreover, it is due to digital reasons, assuming that the late film release (this is not PS, but equivalent to the process of film development) is not handled seriously, no amount of effort in the early stage may be able to produce a truly high qualityFilm.

● White balance ——Our eyes can automatically adapt to different ambient light, interpret the brightest place as white, and other colors to explain in order.But the sensor does not have this function of the human eye, it must know how bright it is white, so we need to set the white balance to tell it.When shooting with Raw, the sensor records only the brightness value of each pixel, and the white balance is recorded as metadata, which is used in the later conversion of RAW Converter.It is equivalent to a starting point. The picture of Li Yasi pepper red dragon can also be understood as an essential parameter in the conversion function. Without it, other colors cannot be explained.Before the Little Revolution, there seemed to be an article about the problem that white balance can be restored at a later stage regardless of whether it is set or not.My opinion is absolutely positive in theory, why is it "in theory"?From the above discussion, we can know that the setting of white balance is only involved in the later conversion.So even if the correct white balance is not set at the time of shooting, as long as the correct color temperature value of the scene at the time can be input during the post-conversion, the original color can definitely be restored.The question is, how many people can accurately remember the color temperature value at the time of conversion.Unless there is a pure white reference in the picture, the color can be set correctly by using a white balance straw to absorb the color.In fact, here is also a trick worth trying: when taking a photo, place a white object (such as white paper) in the composition, but pay attention to the place that does not affect the composition, and the area should not affect the exposure reading tooLet it be fully exposed to the light of the scene), and shoot it in.In the later conversion, just use a white balance straw to suck the white object, and then cut off the white object.
However, for shooting JPG, it is not the same thing.Because after the shooting, the camera internally converts it to JPG, which means that it must use the color temperature value for calculation.If the white balance has not been set before, it must be a color cast.
● Color interpretation ——If you ask a thousand people which color is red, you may get a thousand different reds.For the same reason, for CCD / CMOS, it does not know what exactly is red, blue, and green.Therefore, when we convert RAW files, we must specify the definition of red, blue, and green, which is the color space. Different digital cameras have built-in different color spaces, such as sRGB, AdobeRGB, etc.For this point, my understanding is that when shooting RAW format, setting sRGB or Adobe RGB in the camera is useless, because the definition of RGB is only converted (that is, the target Color Space, the Color Space of the converted file) Tell RAW Converter, so there will be a Color space option when converting RAW files, you must specify this target Color Space.So, if we are shooting in RAW format, do nt ask if you want to set it to sRGB or AdobeRGB. If you like, you can even convert to ProPhoto RGB!I am afraid that the pursuit of image quality is not very high when shooting JPG, so I use sRGB.
● Gamma correction ——First of all, you should know what Gamma is. You can search the relevant information online.Digital RAW format shooting uses linear gamma (that is, gamma 1.0), but the human eyes light induction curve is a "non-linear" curve.Therefore, RAW Converter will apply a Gamma curve to Raw data during conversion (simple understanding is equivalent to performing an f (x) transformation on the original data, and note that f (x) is not a linear function), To produce a hue that is closer to the human eye.
● Noise reduction, anti-aliasing, and sharpening ——When the image details just fall on the unit pixels in the CCD matrix, or assuming it falls on an R-sensitive pixel and B-sensitive pixel, the problem arises.The true color light * "anti-mosaic" operation at this detail is difficult to accurately restore, which means that the details will be lost.Therefore, most RAW Converters will perform a series of operations such as edge detection, anti-aliasing, noise reduction and sharpening during conversion.Because the algorithms used by different software may not be the same, the reason why the details of the films produced by different RAW converters are different is this.

Having said a lot, I will introduce the following steps

The original picture is dark





Adjust color


Adjust contrast


Any work that can be done with Camera Raw should not be saved in PS after conversion. The reason here is simply to say: there is a fundamental difference between the pre-conversion and post-conversion operations. The various pre-conversion operations are actually defining a series of parameters (such as color space, sharpening value, whiteBalance, contrast, noise reduction, etc., and then handed over to the conversion function (in fact, Dcraw, an open source software, Dave Coffin.How powerful he is, look at the following RAW Converter software, all based on Dcraw: Adobe Photoshop, Bibble, BreezeBrowser, Conceiva Lightbox, cPicture, dcRAW-X, Directory Opus Plugin, dpMagicGraphicConverter by Thorsten Lemke, IrfanView, IRIS image processor for astronomers, Lightbox, Photo Companion, Photo Jockey, PhotoReviewer, PolyView, PowerShovel-II, RawDrop, RawView, SharpRaw by Duane DeSieno, SilverFast DCPro, ViewIt, Viewer n5, VueScan) to generate the color information of the target pixel.Equivalent to a f (x), f (definition of color space, sharpening value, white balance, contrast noise reduction) = the color of the target pixel, as long as this color value does not exceed the color gamut of the target color space, it is a valid colorinformation.However, if it is converted to a smaller color gamut, some colors will be cut off (that is, the color of the target pixel exceeds the color space (such as when converting an image with rich color information to the sRGB Color space).However, after the image has been converted (developed), and then performed in PS, such as Level, Curve, Hue / Saturation, etc., are performed based on the existing pixel color values, and are non-linear *.Will cause irreversible loss of information.For example, a non-linear conversion f (x) = x ^ 2 (the square of x), x = 3 or x = -3, the result is all 9, and the color information must be compressed.Another example, Camera Raw 2.The functions provided by Exposure and Shadows in 4 are equivalent to White Point and Black Point in Level in PS, then suppose we set the point with brightness value of 245 as the white point (255)The two-degree points from 245 to 255 all turn white, which seems not to be a problem.But the most fatal thing is that the points from 0 to 245 are all stretched to 0 to 255. Where does the color information that is not in the middle come from?Those are the colors that are "made up" and calculated using an interpolation algorithm.This is why after looking at the histogram after applying Level, you will see that there are a lot of discontinuous broken lines in the middle (I will not explain it here, if you are quite familiar with PS Level, you should understand it).However, what is the difference if Exposure is set in Camera Raw?In Camera Raw, only a parameter value is actually given, and the function is to recalculate all pixels, so the valid pixel color information is obtained.babygolden是什么酒The brand of fish feed is good&Koi fish picture big picture~Why no grass goldfish$Dragon and Phoenix Koi!Grass goldfish and koi are better to keep#Grass goldfish feed?Grass goldfish and koi are more expensive^How old can grass goldfish grow%Lion head goldfish@

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