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J.R. Photoblog - Articles & Tutorials » Blog Archive » Basics - Opening the RAW file in Photoshop - Why 16 Bits?
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Basics - Opening the RAW file in Photoshop - Why 16 Bits?


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This is a personal choice, but I almost only use my raw converter (Adobe Lightroom) for its picture library manager.

Before opening

Before opening my RAW in Photoshop CS2, I adjust the white balance and I take care to reset all others default settings to preserve the maximum original data from the sensor and thus the highest dynamic range. I especially pay attention to disable the sharpen setting because I’m about to edit my picture and some treatments give bad results with a sharpened source. Sharpening is, most of the time, the last thing I do on the flatten picture, here is why :

  • Spep 1 : On the left the exported picture in photoshop with sharpening, on the right the same picture without sharpening
  • Step 2 : I add the same heavy postprocessing on both pictures to bring out the problem
  • Etape 3 : We can clearly see that the postprocessing showed up white outlines around the chimney, it also accentuated the noise in the sky
  • Etape 4 : I add final sharpening to the right picture, this is perhaps a question of taste but I much prefer this result :P

 
nosharpen.jpg

Editing in 16-bits per channel

My RAW source has a 12-bits precision, so if I export it in 8-bits I cut off 4-bits of precision per channel, in other words I exclude some shades from my picture. So if I want to preserve all data from this source, this is quite evident that I need to work in a space wide enough to host its full depth. Under Photoshop the next bit depth is 16-bits per channel and, because 12-bits is a subset of 16-bits, this is lossless.

Did you already ask yourself “I am working in 16-bits, why the hell do my color picker still show me values from 0 to 255 (28 = 8bits) for each channel instead of 0 to 65535 (216 = 16bits)?”, no ? because I really wondering why :D .

I found three possible answers on the web :

  • The first one I found was “Because a histogram that would show a scale with 65536 discreet levels would be too big, you would need a display that is 65536 pixels wide”, I found this one quite disputable because it is just a matter of scale and that’s always possible to add a zoom option to that histogram.
  • The second one was “If you display a gradient from blue to black with 256 shades and another with 65536 shades, there is a few chance you can see the difference, so the internal process of Photoshop is indeed in 16-bits but the screen output is rendered in 8-bits”, I am more convinced by this one but I already read that the human eye can discern about 500 shades of a single color, in other words approximately 9-bits
  • The third one is very close to the second one, it was something like “Monitors and video cards are working in 8-bits per channel, so it is useless to ask them to display a 16-bits picture since they are not capable of that, the internal process of Photoshop is indeed in 16-bits but the screen output is scaled to 8-bits”, I accepted this answer but now I just wonder how you can take advantage of these famous laCie monitors which claim to display a 12-bits color depth seeing that the screen output of photoshop is 8-bits, video cards are 8-bits (I saw that some of them are able to display a 10-bits precision … but 10 is not 12), so finally is the accuracy of these monitors inexploitable or do I miss something ? If you know more about this subject, please share it to us ;) .

In short, the most important thing is that even if the screen output, the preview is scaled to 8-bits, we really work in a 16-bit space and that’s something easy to verify:

1. I take a gradient from blue to black, no visible difference between 8 and 16-bits

8bit_vs_16bits_1.jpg

2. Now I select a small portion of this gradient and I resize it to 100% wide to get a new gradient with a very small amplitude, still no visible difference between 8 and 16-bits and that’s normal

8bit_vs_16bits_2a.jpg

8bit_vs_16bits_2b.jpg

3. No I add a levels adjustment layer and I adjust it to contrast the picture and to bring out the quantity of shades recorded in this “mini gradient”

8bit_vs_16bits_3.jpg

4. The reassuring result, there is many more steps in 16-bits than in 8-bits

8bit_vs_16bits_4.jpg

I edit my pictures using a non-destructive process, I mean that my original is always the first layer and I stack adjustment layers above it.
In a 8-bits/channel color mode you can quickly have a visible deterioration of your picture with some layers combinations, mostly if you are using multiple layers with gradient masks like I do. Sure this is often our fault like a bad order in layers for example … but in 16-bits, I rarely reach other limitations than those of the source itself or you must do it intentionally :roll: , in short, editing in 16-bits per channel offers more flexibility.

The purpose of the exaggerative example below is to show that, despite of an intentional degradation of the source (heavy uncontrast + heavy contrast), the depth of 16-bits allow a much better preservation of the picture.

8bit_vs_16bits_photo.jpg

12 Comments »


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    G’day from Australia Julien, thankyou for this tutorial. I have only usually worked in 8 bit and never really understood the difference (mainly because I couldn’t see any on the screen :). I have a question about your masking and layering process (if you are willing to reveal your trade secret)? Do you use a duplicate layer to modify? How do you use masking as I have tried a small amount but really struggle with it? Hope you can help with another tutorial. regards Graeme

    Julien : I try to have the less possible real picture. Most of the time I only have my original as the first layer and adjustment layers above it with masks. However, sometimes, I need to duplicate the original for some specific destructive filters like denoisers.

    Comment by Graeme Baynes — August 7, 2007 @ 7:42 am


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    Bonjour Julien!

    Fantastique petit tutoriel que tu nous présentes là! Je vais le conseiller à plusieurs amis graphistes et photographes. Continue ton excellent travail comme photographe et comme rédacteur de ces bons petits tutoriels :).

    P.S. Petite rectification √† d√©battre: Je suis graphiste et selon mes cours de couleur, l’oeil humain ne discerne environ que 200 tons de gris, du noir au blanc.

    Julien : Merci pour cette info Olivier, effectivement √ßa reste √† d√©battre mais je n’en ferais rien puisque les diverses sources que j’ai pu voir √† ce sujet disent toutes des choses diff√©rentes et semblent √™tre s√Ľres qu’elles ont raison … mais c’est pas bien important ;)

    Comment by Oliver — August 31, 2007 @ 4:49 pm


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    my biggest problem is b&W,i dont like my D70s’s b&w results in photoshop,but i love your b&W tones,i d like know your illusion on your b&w photos..thanks

    Julien : I take all picture in RAW (color), results are due to the conversion and post-processing under photoshop, I will post a black and white tutorial in the near future, but right now I don’t have enough time :|

    Comment by serkant — November 22, 2007 @ 2:25 pm


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    Many thanks, I work in 8 bit and I have many problems with artifacting. do you have recomentations?

    Julien : Yes, edit in 16 bits :). If you are talking of JPG artifacts then shoot in RAW.

    Comment by Juan Carlos Herrera — November 29, 2007 @ 2:32 pm


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    Thanks for an informative article. I have one question I hope you’ll be able to help me with.

    When I know I need to do a lot of processing of a RAW file I open it at 16 bit in Photoshop. Now when I’m done and need to save as jpg to put on my photoblog I first convert to 8 bit and ’save for web’ as a jpg.

    This often causes the photo to go very ‘flat’. A lot of the colour and lumination is lost. I understand 8 bit is a lot smaller colour space than 16 bit, but it still should not be that different. For example I can open the jpg and increase saturation and contrast and get a lot closer to what it looked like before I converted the 16 bit file.

    Do you have a work flow to avoid this?

    Thanks,
    Jesper Garde

    Julien :
    Yes, your problem is a very common one and has nothing to do with 8bits or 16bits ;) .
    You probably edit you picture in another profil than sRGB which is the default format for web export. There are good chances that you edit it in AdobeRGB or ProPhoto RGB which is a good thing, but you need to convert it to the standard web profile (sRGB) before saving it.
    1. Save your source PSD file
    2. Flatten picture (Layer > Flatten image)
    3. Resize picture to the desired web format (Image > image size)
    4. Convert image color profile (Edit > Convert to Profil …> Destination Space : sRGB IEC61966-2.1) (note that you can see in “source space” the profile you were using)
    5. Convert image to 8 Bits (Image > Mode > 8Bits / Channel)
    6. Use “File > Save As” instead of save for web (save for web is more a web designer tool), you will preserve your EXIF metadata
    Voilà!

    Comment by Jesper Garde — April 25, 2008 @ 3:46 pm


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    Whether others might agree or disagree with the advantage of 14-bits against RAW 12bitRAW shooting and 8-bit against 16-bit postprocessing, I prefer shooting 14-bits all the time while “it doesn’t hurt” and while I’m sure it contains more information especially for highlight and shadow detail. Related to your sharpening tutorial: Thanks for posting your thoughts. Interesting.
    Kindest regards,
    Stany Buyle

    Julien :
    I would do the same thing because “it doesn’t hurt” however I think all this is an illusion… In my opinion, a 12bits container was already very large to hold the sensor data. I don’t think there would be a significant difference in the richness of the picture between a 12-bit and a 14-bits container…

    Comment by Stany Buyle — August 28, 2008 @ 12:51 am


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    I’m really impressed with your pictures Julien and as I have the same camera I feel a bit…how to say…unable compared to you..my question is,what your digital process flow?I mean,you open the picts directly in Camera Raw and than Photoshop or you convert them with Nikon SW.I red many times that Nikon SW is the best to convert RAW files.And if you do use Nikon SW,what kind of setting(sharpening,white balance etc..) you change from there and what do you leave to PS?Thanks for sharing with us all this beauty and all this knowledge.Keep the good work going!Marco

    Julien :
    Thanks Marco, I don’t know Nikon SW, perhaps are you talking of Nikon Capture NX ? Personally I use Adobe LightRoom because I like it as a Raw browser, I just adjust the white balance and then I open the picture under Photoshop. The engine of LigthRoom is the same than Camera Raw. It is known that Capture NX is better than Camera Raw for the Nikon Raw format but NX is not enough user friendly for me and I find the quality of LightRoom sufficient for my needs. About my settings there is no magic formula, all settings depends on the picture and all pictures are different so this is a question of context and taste. ;)

    Comment by marco — November 15, 2008 @ 9:08 pm


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    about the bits :)
    as i see it, is that
    1. Photoshop doesn’t “see” pictures as a human does. for us picture is … picture, but for computer picture is an aggregation of numbers.
    2. how Photoshop works you can divide into modules. like [read], [process], [write], [display]
    1 + 2 . modules can be completly independent from one another. while the [display] module sends picture to the screen in (for example) 8-bits - maybe display drivers allow to resample only 8-bit depth(?), you can still work with 16-bits, because the [process] module works in 16-bits.
    like i said - picture is only a set of numbers, while working on it, for the computer, it is like erasing digits from an array and replacing them with another digits. for us to see the results computer has to interpret the numbers, convert them from 16 to 8-bit and finally show as a picture.
    if you are using a video card and a monitor that can display 10-bits or 12, Photoshop just don’t cut 8 from 16, but 6 (4) bits.
    hopefully made myself clear enough :)

    Julien :
    Thanks for this explanation, I was just wondering if 10 or 12 bits video cards was something common or just some kind of inaccessible / elitist stuff. If all common Nvidia / Ati cards are truncating bit depth to 8Bits then 10/12 Bit monitors are just useless? Am I right or do I misunderstand something?

    Comment by engineer in depression — May 30, 2009 @ 5:31 pm


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    “If all common Nvidia / Ati cards are truncating bit depth to 8Bits then 10/12 Bit monitors are just useless?”
    if yes, than yes - it’s like building 3-line highway and than using only 2, or for example buying a Ferrari and driving it only to the nearest grocery :) - never using its real possibilities.
    but i do not know what is the “bit-rate” of the most common video cards. i think that every time someone is building his workstation, it is to be considered if all of the components are up to each other. otherwise money will be simply waisted…

    Julien :
    Thanks again, you are confirming what I was thinking. Anyway I bought a 10 bits laCie screen and I can see much more shades than with my previous one but its probably simply a question of quality more than a question of bit depth ;) .

    Comment by engineer in depression — June 12, 2009 @ 9:14 pm


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