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#1
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"Why Raw" Article
I have written Part I of an article titled "Why Raw". The article can
be found on my web site at: http://ronbigelow.com/articles/raw/raw.htm Other articles can be found on my site at: http://ronbigelow.com/articles/articles.htm Comments are always welcome. |
#2
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Very informative.
Thank you! "ron" wrote in message oups.com... I have written Part I of an article titled "Why Raw". The article can be found on my web site at: http://ronbigelow.com/articles/raw/raw.htm Other articles can be found on my site at: http://ronbigelow.com/articles/articles.htm Comments are always welcome. |
#3
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[]
"ron" wrote in message oups.com... I have written Part I of an article titled "Why Raw". The article can be found on my web site at: http://ronbigelow.com/articles/raw/raw.htm [] Comments are always welcome. Ron, There is a major error in the article, section Raw Advantage #2: Bits, making the comparison between JPEG and RAW quite incorrect. The data in JPEG files has a gamma correction of (typically) 2.2 applied, which means that it can accommodate a far greater dynamic range than just 255 linear light levels. The difference between RAW and JPEG in is the accuracy of light level representation, not in the dynamic range. Cheers, David |
#4
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Tnx for article, it's great. I'm reading the rest of your work...
"ron" wrote in message oups.com... I have written Part I of an article titled "Why Raw". The article can be found on my web site at: http://ronbigelow.com/articles/raw/raw.htm Other articles can be found on my site at: http://ronbigelow.com/articles/articles.htm Comments are always welcome. |
#5
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David,
The 255 light levels have to do with tonal range not dynamic range. The article assumed a 5 stop dynamic range camera. That is fixed. The camera can not exceed that. The gamma curve can make the image more contrasty and make it appear to the eye that there is more dynamic range. However, that will simply readjust the spread of the 255 light levels (compressing some and spreading out others), but there will still only be no more than 255 light levels in a JPEG file. The article is correct. |
#6
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ron wrote:
David, The 255 light levels have to do with tonal range not dynamic range. The article assumed a 5 stop dynamic range camera. That is fixed. The camera can not exceed that. The gamma curve can make the image more contrasty and make it appear to the eye that there is more dynamic range. However, that will simply readjust the spread of the 255 light levels (compressing some and spreading out others), but there will still only be no more than 255 light levels in a JPEG file. The article is correct. The way I'm understanding it, "Figure 4: Shades vs. Stops of Light" for JPEG is wrong. When you half the exposure, while in the RAW file the digital value will be halved, this does not happen in JPEG. The values would be (approximately) 255, 186, 135, 99, 72, 52 etc. The JPEG has twenty different tonal values four stops down and five stops down from peak white, and 69 different tonal values between peak white and one stop down. You article gives 16 and 128 shades for these values. David |
#7
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David J Taylor wrote:
ron wrote: David, The 255 light levels have to do with tonal range not dynamic range. The article assumed a 5 stop dynamic range camera. That is fixed. The camera can not exceed that. The gamma curve can make the image more contrasty and make it appear to the eye that there is more dynamic range. However, that will simply readjust the spread of the 255 light levels (compressing some and spreading out others), but there will still only be no more than 255 light levels in a JPEG file. The article is correct. The way I'm understanding it, "Figure 4: Shades vs. Stops of Light" for JPEG is wrong. When you half the exposure, while in the RAW file the digital value will be halved, this does not happen in JPEG. The values would be (approximately) 255, 186, 135, 99, 72, 52 etc. The JPEG has twenty different tonal values four stops down and five stops down from peak white, and 69 different tonal values between peak white and one stop down. You article gives 16 and 128 shades for these values. David Ron: Concerning your writeup at http://ronbigelow.com/articles/raw/raw.htm See Figure 7 at: Dynamic Range and Transfer Functions of Digital Images and Comparison to Film http://www.clarkvision.com/imagedetail/dynamicrange2 While in a jpeg file there can be no more than 255 levels, those levels do not have to be linearly distributed. In fact they are not, just as Figure 7 above shows. Note in that figure the dynamic range of the jpeg and the raw file cover the same range, except for a slight increase in noise at the low end. Of course, the 12-bit raw has more precision, and that is the main difference between the two. You might also check out: Digital Camera Raw versus Jpeg Conversion Losses http://www.clarkvision.com/imagedetail/raw.versus.jpeg1 The statements about digital camera dynamic range of the "better cameras" have about 5 stops is incorrect. The better cameras (e.g. DSLRs) are Poisson statistics limited (meaning photon statistics limited by the sensor's given quantum efficiency). The sensors have over 12-bits dynamic range and thus are limited by the 12-bit ADC. See Table 3 at: The Signal-to-Noise of Digital Camera images and Comparison to Film http://www.clarkvision.com/imagedeta...gnal.to.noise/ Roger |
#8
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In message ,
"David J Taylor" wrote: There is a major error in the article, section Raw Advantage #2: Bits, making the comparison between JPEG and RAW quite incorrect. The data in JPEG files has a gamma correction of (typically) 2.2 applied, which means that it can accommodate a far greater dynamic range than just 255 linear light levels. The difference between RAW and JPEG in is the accuracy of light level representation, not in the dynamic range. An 8-bit TIFF has more potential shadow detail than a 12-bit RAW file. It is not usually realized, however, as 8-bit TIFFs generally come from 12-bit RAW files. -- John P Sheehy |
#9
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In message .com,
"ron" wrote: David, The 255 light levels have to do with tonal range not dynamic range. The article assumed a 5 stop dynamic range camera. That is fixed. The camera can not exceed that. To say that a camera has 5 stops of dynamic range and no more assumes a certain quality standard. With a definition that gives 5 stops for DSLRs, you are talking about a standard of very high quality shadows. The fact is, there is no hard, concrete limit on the dynamic range of an image if your quality standards are flexible; the quality simply deteriorates as you go deeper and deeper into the shadows, until noise dominates and the signal is vague and lost in the chaos. The gamma curve can make the image more contrasty and make it appear to the eye that there is more dynamic range. However, that will simply readjust the spread of the 255 light levels (compressing some and spreading out others), but there will still only be no more than 255 light levels in a JPEG file. The article is correct. A JPEG can only express 256 light levels for each color channel. Most of the values less than about 50 only occur by demosaicing and sharpening when they come from a 12-bit RAW file. If you took each RAW color channel and made a bitmap from it in 8-bit gamma-adjusted space, with no sharpening or softening applied, most of the values below 50 would not be used at all. The histogram would be spaced like this: | | | | | | | |||||||||||| The section to the right, where the histogram is full (without gaps) is the range where the 12-bit RAW has more level-definition than the 8-bit gamma-corrected space. The rightmost section has several RAW values becoming a single 8-bit value. -- John P Sheehy |
#10
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ron wrote:
I have written Part I of an article titled "Why Raw". The article can be found on my web site at: http://ronbigelow.com/articles/raw/raw.htm Other articles can be found on my site at: http://ronbigelow.com/articles/articles.htm Comments are always welcome. Thanks again. I only have one comment: It would be cool if you made your articles in an easy to print format, like pdf. I wanted to read it this morning, but was running a little late.... I could've printed it and read it during my lunch break. -- Slack |
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