![]() As it was already mentioned, curved metal and glass surfaces are the first candidates for these specular highlights, as well as all of the sources of light in the image.Īnd two final notes to those of you who decided to experiment with your cameras: If some highlights that are specular in nature do not have overexposed pixels even if looking at 100% magnification the image should normally be considered as underexposed. ![]() On a normally exposed image, you will have at least a few of the overexposed pixels in every major specular highlight (if there are such highlights in the scene, of course). Note: If your camera is one of those with white balance pre-conditioning, you will need to enter per-channel values in Manual per channel section R, G, B, G2 fields Now we can go into Preferences and, following the conservative approach, enter this second number to Overexposure Detection section in Manual level all channels field. 9 and 10 for Sony A7R, we will see that here the peak value is 15860, while the bulk of the structure starts at 15635. So, if we return to the histogram shown on figs. However for something like we have on fig.22, which is not a pure “hit-the-wall”, the clipping starts at 3935. For “hit-the-wall” and “spike” types of highlight structures, it is the spike itself. ![]() The conservative approach is to consider the value that starts the overexposure “structure” to be the maximum, as the higher values are mostly pattern and processing noise. Which value should be considered as practical maximum? Color channels preconditioning zoomed in. This is because of how the preconditioning is implemented – it is digital multiplication of data in red and blue channels by a number slightly higher than 1, applied before the data is written into a raw file.įigure 25. Zoom to blown out highlights - maximums are different for different channelsĬameras where color channel preconditioning is used are recognizable by the regular one-pixel gaps in the histograms of red and blue channels (sometimes, additionally, they have different clipping points for red, blue, and both green channels, as on fig.24). In our case, it is what we want as we will be analyzing how the clipping exhibits itself on the shots like these from Imaging Resource:įigure 24. Here we will try to demonstrate the typical “looks” of the histogram of the clipping zone.Īny curved metal or glass surface is a good source of specular highlights. It is important to recognize the look and calculate the practical clipping point, which is not always the same as the maximum raw value. It is useful to know how to determine practical clipping point for at least two reasons: the most common is that we need to know clipping point to determine the headroom in highlights and tune the camera settings to provide more reliable overexposure warning (“blinkies”) another one is dynamic range analysis (signal-to-noise ratio, SNR), and measurements of utilized well capacity (full well capacity, FWC, is seldom used in modern cameras).ĭifferent cameras, even if based on the same sensor, may render extreme highlights around the clipping point differently and differently, even with different values of clipping points, depending on ISO setting. Depending on the quality demanded of the image (which will depend on presentation size, viewing distance, other viewing conditions such as screen resolution, etc.,), the practical dynamic range for the specific camera will be different, even for the same ISO setting.Study of the highlight clipping using RawDigger histogram It's just that with the lowering of exposure, small details disappear, the contrast between bigger details diminishes, color fidelity becomes worse. In reality, any practicing photographer knows that the degradation of the image in the shadows (or because of low exposure) happens gradually, there is no strict demarcating line. With this, the nature of noise (for example, random noise, banding) isn't accounted for, however the noise character is important for visual quality. Unfortunately, the public data on DR is limited to "DD - ISO sensitivity" graphs and tables. In today's world, "dynamic range" (DR) has become, in the minds of (many) photographers one of the main characteristics of a digital camera. ![]()
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