3/28/2023 0 Comments Rawdigger histograms part 1![]() Shooting RAW at 14-bit will give us a LOT more room. In theory, if you are targeting 8-bit output, you are basically guaranteed posterization if any one of your color channels uses up less than 6% of the total histogram on a 12-bit capture (8-bit has 256 values, and 6% of the 4096 values in 12-bit is just 245 values). The problem gets even worse, since the bit-depth is per color channel, and typically your blue color channel on the negative will carry less information than what you see in the total histogram.ĭuring the conversion process, the information is stretched out to fill the histogram, and if there isn’t enough levels of information, then you will create gaps in tonality, i.e. Then let’s say that the exposed part of the negative only uses up 1/4th of the total histogram of your camera sensor, then you only capturing ~1,024 distinct levels of information (which is another way of saying you only capture 10-bits of information, 2^10 = 1024). “12-bit” is just another way to say that there are 4096 potentially brightness values available to store the information of each color channel (with 0 being black and 4096 being max brightness). Let’s say you are capturing your negative using a 12-bit RAW file. But you are losing tonal smoothness, and creating the potential for posterization during conversion. Yes, I think this is true, although I’m not sure I would say you are “losing” information, since there are no values that fall outside of the range of the sensor. It therefore stands to reason that, when scanning a low contrast negative that doesn’t utilise the DSLR’s full dynamic range, one is losing a lot of potential information. My question is whether it is possible, either practically or theoretically, to compress the dynamic range of a DSLR in this way, since I have never heard of something like this being done. This means that all the sensor’s ‘bits’ would be recording important information. This is because the high and low ends of the sensor’s dynamic range are recording nothing, whereas with a smaller, compressed dynamic range they could be recording data from the negative. If I understand correctly, dynamic range measures the difference between the darkest and lightest values a sensor can record simultaneously, and the bit depth measures the number of recorded values between these points. Unlike B/W, I’ve noticed that the information from colour film only takes up a small proportion of the histogram, and therefore the dynamic range of the camera. So I’ve been scanning film with a Nikon d750 for quite a while, B/W initially but recently colour. But yeah I suppose a bit of extra quantisation noise from this histogram quirk doesn't do much.(I’m pasting this from a post I made on DPReview, since I’m interested in getting the opinions of NLP users as well) But again I get the same histogram pattern with ISO 125 shots.Īs for the noise level yep there's a lot of it but I stack bursts (usually at least 20 frames, though I'm thinking of going higher) which reduces noise quite a bit, so at that point getting the offset right can make a difference I suppose, mostly if like I said added gain and WB end up boosting that offset quite a bit. Here's the dark frame, I'll spare you any suspense, here's the histogram: Īs for any noise reduction I just looked and I do have "High ISO speed NR" set to "Standard", but I don't think it (and sure hope it doesn't) affects the RAW. ![]() In fact I just looked at a much older daylight ISO 125 shot taken with my old G9 X (I currently have both a G9 X and a G9 X II) and it's no better: < the histogram is perfectly antialiased, it's no visualisation artifact, that's exactly how it is, you've got the strict 12-bit comb pattern that gradually fades as you go up in values. I had a look at full raw picture histograms with daylight pictures at ISO 125 or even darker shots at ISO 6400 and we've got the same pattern around 2048. ![]() ![]() For what it's worth I took another burst just a couple of minutes later (same settings except higher ISO) and all these files in that burst have exactly "black 2049, cblack 0 0 0 0" ![]()
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