sRGB Color Space: Is 16 bit Preferable to 8 bit?

[TomBrooklyn]

When processing photos in the sRGB color space, can better quality be achieved by using 16bit, as opposed to 8bit?


Is it even possible to use 16bit with sRGB?


When Adobe Lightroom 4 sends a photo to Photoshop (or any other photo editor) for editing, it gives a choice of sending it in 16 or 8 bit.

 

[KmH]

The bit-depth is a separate consideration from the color space.

Image editing experts recommend editing using the widest color gamut available, which essentially means editing in the ProPhoto RGB color space.
The web, and most other electronic displays, can only display a relatively small color space and are essentially limited to sRGB.
The web and most other electronic displays are also 8-bit.
Consequently, the intended use of an image determines what color space it is assigned to, and that assignment is usually one of the final post productions steps done after any editing.

sRGB has one of the least broad of the RGB color gamuts. Adobe RGB is broader than sRGB too.

Lightoom's Develop module uses a RGB color space very close to ProPhoto RGB, and ProPhoto RGB is one of the export color space choices.

8-bits can only encode 256 gradations of tone per color channel. 16-bit, as far as Photoshop goes, can encode 32,768 gradations of tone per color channel.
So editing in 16-bit mode and using 16-bit capable editing tools makes it very much less likely your edits will result in banding, posterization or moiré.
Some of the tools in Photoshop can only be used when an image has an 8-bit color depth.

Color space - Wikipedia, the free encyclopedia
Gamut - Wikipedia, the free encyclopedia
http://www.focalpress.com/uploadedF...raphy/Evening_e9780240522005_pages306-309.pdf

• Color Management, Part 1: Concept & Overview
• Color Management, Part 2: Color Spaces
• Color Management, Part 3: Color Space Conversion
• Understanding Gamma Correction & Digital Tones

Adobe Photoshop Lightroom 4 Book: The Complete Guide for Photographers

Adobe Photoshop CS6 for Photographers: A professional image editor's guide to the creative use of Photoshop for the Macintosh and PC

Adobe Photoshop * Image essentials

 

[Garbz]

When processing photos in the sRGB color space, can better quality be achieved by using 16bit, as opposed to 8bit?
Is it even possible to use 16bit with sRGB?
When Adobe Lightroom 4 sends a photo to Photoshop (or any other photo editor) for editing, it gives a choice of sending it in 16 or 8 bit.

Yes
Yes
Chose 16bit.

Longer answer:
The concepts of colour space and bit depth are completely independent. Colour space determines what colour a certain value has, i.e. RGB(255,0,0) is actually x:0.64, y:0.33, and Y:0.2126 on a CIE 1931 space. In AdobeRGB the same xyY co-ordinates are represented by RGB(219,0,0), so AdobeRGB is said to be a larger colour gamut as it can display colours that sRGB can not.

BitDepth determines the granularity of possible colour choices within a gamut. So the value of RGB(255,0,0) in 16bit is represented as RGB(65535,0,0). The next value down is is RGB(254,0,0) and in 16bit that is RGB(65280,0,0), which is a whole 255 shades that can be represented in 16bit that can't be represented in 8bit. These shades may not be relevant to your vision, but become very critical when processing an image and doing things like increasing or decreasing brightness, contrast etc.

Now to blur the lines a bit. 8bits (16.7million colour combinations) are enough to display every discernible value in the sRGB space. However when you work in a larger colour space like AdobeRGB or ProPhotoRGB then you need to increase the number of colours otherwise you end up with some colours which may be distinguishable but can't be represented i.e. between RGB(0,254,0) and RGB(0,255,0) there may actually be more colours but we've run out of numbers to play with. 16bits provide you with281 trillion possible combinations.


So in summary if you can pick a larger colour space, then do. If you can pick a larger processing bitdepth, then do. If you're going to pick a larger colour space you need to pick a larger processing bitdepth.

 

[TomBrooklyn]

...Image editing experts recommend editing using the widest color gamut available, which essentially means editing in the ProPhoto RGB color space.
...Adobe RGB is broader than sRGB too.
...Lightoom's Develop module uses a RGB color space very close to ProPhoto RGB, and ProPhoto RGB is one of the export color space choices.

Thanks for your response, but I'm having a little trouble finding an answer to my question in it. Please note that I'm asking about bit depth in the sRGB color space. I'm not looking for a comparison of sRGB to Adobe 1998, ProPhoto, or Melissa (Lightroom.)

When processing photos in the sRGB color space, can better quality be achieved by using 16bit, as opposed to 8bit?
Is it even possible to use 16bit with sRGB?

Yes
Yes
Longer answer:
...In AdobeRGB
...8bits (16.7million colour combinations) are enough to display every discernible value in the sRGB space. However when you work in a larger colour space like AdobeRGB or ProPhotoRGB then you need to...

Thanks for your response. I was doing fine with the first part; but your elaboration has me dazed and confused. Not because I am unfamiliar with the Adobe1998 and ProphotoRGB color spaces; but because my question is not about them, and it seems like your answer is. Could you please clarify your response relative to the sRGB colorspace only?

 

[Ysarex]

Grabz direct answers are correct, yes and yes. Your photo can be 16 bit in Photoshop and your working color space can be sRGB. If you're going to edit that photo (make changes) then it's immensely beneficial that the photo be 16 bit. It so immensely beneficial that the photo be 16 bit that it's fair to say that editing an 8 bit photo is just wrong. Think of it as data density and you're editing is rearranging that data. With lots of data any changes you make are less likely to show -- the data doesn't have to be stretched thin. The same applies to colorspace in that the ProPhoto colorspace is more data dense than sRGB or Adobe RBG -- sRGB being the least data dense. So when editing is taking place chose maximum data density. Once the editing is finished you can reduce the data density to only what is essential. The bit depth factor is by orders of magnitude more critical than the colorspace factor so that I would not be too concerned about editing a 16 bit sRGB photo (however I don't do that) but I would strongly resist editing an 8 bit photo no matter what the colorspace. As Grabz noted 8 bits and a more data dense colorspace is ridiculous in the same way that telling you to put 5 gallons of water into a quart jar is ridiculous.

There's a good reason LR's default colorspace is ProPhoto and you can't change it. Lr's job is to create the RGB photo from the raw sensor data. As the process begins we have and should expect maximum data density. During any editing we maintain maximum data density. Eventually as we process the photo we're going to reduce that data density, but only at appropriate junctures in the process. It's appropriate to reduce the data density when alterations to the data are complete. If the processing in LR is sufficient there's nothing wrong with outputting an 8 bit sRGB photo, but that photo should not be further edited. If further editing in Photoshop is planned then the best alternative is to transfer the RGB photo into Photoshop and maintain maximum data density -- 16 bit ProPhoto. When the editing in Photoshop is completed reduction to 8 bit and sRGB is appropriate.

Joe

 

[Big Mike]

The best workflow, is to maintain as much information (larger color space, high bit level) as long as possible. When you are finished editing, and you have a specific use for the image...then you can 'save down' to the appropriate level.

For example, it would be best if you edit your images while in a large color space, but web browsers are designed for sRGB only...so if your intended use is to display on the web, you will want to export a version of the image that optimized for that.

 

[Gavjenks]

I recommend NOT using any color space other than sRGB, unless you really know what you're doing and have some specialty needs (like if you're printing in a high end published bound book, and know that when you're shooting and editing).

Changing between color spaces means that the edits you made may not look like you thought they looked (mainly the colors that are in one space but not the other must be changed somehow as a matter of definition), which is obviously bad. Even if the space you edit in completely contains the space you will publish in, that's still bad, because you'll THINK you can display certain colors, but will be wrong. Also, monitors can display sRGB pretty well, but not all of the range of many larger color spaces, so again, you're fumbling around blindly doing things that will probably not translate the way you think they will to the final product. sRGB is standardized and works everywhere, though, so you get exactly what you think you're getting. So again, unless you have specialty needs, use sRGB for no nasty surprises later on, because ANYTHING online, and ANY normal, low end print making services are all going to use sRGB.

However, when it comes to bit depth, you should always edit in the largest bit depth available, because there are zero downsides to that. Except possibly your computer running more slowly if you have a terrible computer. But other than that, no downsides. It prevents data loss and will not EVER cause you to be mistaken about how the final product will look, because your eye can barely even distinguish all the colors in 8 bit anyway, so even if you had a 16 bit capable monitor, you wouldn't be really seeing that much more in 16 bit. But it does do a LOT to protect your data from being lost across multiple edits.

 

[KmH]

...Image editing experts recommend editing using the widest color gamut available, which essentially means editing in the ProPhoto RGB color space.
...Adobe RGB is broader than sRGB too.
...Lightoom's Develop module uses a RGB color space very close to ProPhoto RGB, and ProPhoto RGB is one of the export color space choices.

Thanks for your response, but I'm having a little trouble finding an answer to my question in it. Please note that I'm asking about bit depth in the sRGB color space. I'm not looking for a comparison of sRGB to Adobe 1998, ProPhoto, or Melissa (Lightroom.)

The answers are in the links I provided you.
Reading the links, you might well discover other stuff you didn't know you would want to know.

From my profile - Helping photographers learn to fish

 

[Ysarex]

I recommend NOT using any color space other than sRGB, unless you really know what you're doing and have some specialty needs (like if you're printing in a high end published bound book, and know that when you're shooting and editing).

Changing between color spaces means that the edits you made may not look like you thought they looked (mainly the colors that are in one space but not the other must be changed somehow as a matter of definition), which is obviously bad. Even if the space you edit in completely contains the space you will publish in, that's still bad, because you'll THINK you can display certain colors, but will be wrong. Also, monitors can display sRGB pretty well, but not all of the range of many larger color spaces, so again, you're fumbling around blindly doing things that will probably not translate the way you think they will to the final product. sRGB is standardized and works everywhere, though, so you get exactly what you think you're getting. So again, unless you have specialty needs, use sRGB for no nasty surprises later on, because ANYTHING online, and ANY normal, low end print making services are all going to use sRGB.

However, when it comes to bit depth, you should always edit in the largest bit depth available, because there are zero downsides to that. Except possibly your computer running more slowly if you have a terrible computer. But other than that, no downsides. It prevents data loss and will not EVER cause you to be mistaken about how the final product will look, because your eye can barely even distinguish all the colors in 8 bit anyway, so even if you had a 16 bit capable monitor, you wouldn't be really seeing that much more in 16 bit. But it does do a LOT to protect your data from being lost across multiple edits.

It's pretty clear from the OP's original question that he's using LR 4. LR's working color space is it's own special version of ProPhoto and that's the only color space LR lets you work in. LR saves all the library previews in Adobe 1998 and you have no option to change that either. So if the OP is using LR, as it seems he is, he's editing in ProPhoto and using Adobe 1998. If he's going to edit his photos using sRGB as a working color space he's going to have to get new software.

LR does soft-proof to an output color space and so you can check to see how your image might change as it's output and converted to sRGB. And if your intent is to have an sRGB color space end result, which may of course be very appropriate, then LR's soft-proofing function is a handy thing to have. The OP did also mention Photoshop which likewise soft-proofs color space conversions. If the OP's photo must originate from LR having been edited in the ProPhoto color space and additional editing is called for in Photoshop, then the final soft-proofing and conversion to sRGB is just as well handled -- in fact better handled -- in Photoshop when editing is finished.

I agree that the sRGB color space is the best choice for publishing a photo to the internet or sending it out for inexpensive prints however it's not at all accurate to say that anything (everything) online is going to use sRGB. A whole lot of what's online ignores (or used to ignore) color spaces and in that case a photo saved in the sRGB color space had a better chance of changing appearance the least since sRGB was originally designed to be a best-fit solution to modern RGB display/print hardware. This isn't a case of software online using sRGB but rather a case of software online failing to process the embedded ICC profile and so in fact not using anything in which case an sRGB photo is a best bet. That's not the same as using sRGB. Right now I'm working online with Firefox (very common) and it properly processes embedded color space profiles so I'll see a photo correctly if it was saved in sRGB or Adobe 1998 or ProPhoto. Flickr which is arguably the largest photo hosting site likewise supports/retains ICC profiles. The problem of online software ignoring color space was most aggravating with earlier versions of IE, but IE 10 has now come around and is likewise color space aware. Early versions of Picasa ignored color space but the latest version now has a menu option to activate color management. It's not there yet, but the Internet has to a large degree matured to support proper color management and continues to move in that direction.

Joe

 

[Garbz]

It's pretty clear from the OP's original question that he's using LR 4. LR's working color space is it's own special version of ProPhoto and that's the only color space LR lets you work in. LR saves all the library previews in Adobe 1998 and you have no option to change that either. So if the OP is using LR, as it seems he is, he's editing in ProPhoto and using Adobe 1998. If he's going to edit his photos using sRGB as a working color space he's going to have to get new software.

That's not entirely true. Lightroom works natively in MelissaRGB for all RAW files, whatever the current working profile is for all JPEGs, and softproofs all results to the Monitor colour space as reported by the operating system. In any case this is all academic as Lightroom doesn't give you the option to change the working bitdepth.

Thanks for your response. I was doing fine with the first part; but your elaboration has me dazed and confused. Not because I am unfamiliar with the Adobe1998 and ProphotoRGB color spaces; but because my question is not about them, and it seems like your answer is. Could you please clarify your response relative to the sRGB colorspace only?

My answer was in general terms, and constraining it only to your question would result in you getting only part of the information you need and may lead you astray with other options that Lightroom gives for exports. So in summary:
- 8bit and 16bit have nothing to do with colour spaces.
- 16bit is always better than 8bit for processing as it ensures you don't end up with rounding errors while the processing algorithms are at work. This would result in posterisation (blocky colours, no smooth gradients etc).
- Any bitdepth can be used for any colour space. The colour space determines how wide the possible range of colours is, and the bit depth determines how many of the shades can be represented within that space. In simplistic terms think of 1 bit per channel space (2 possible values for red green and blue). With 1 bpp you can now make the colours: black, red, green, blue, yellow, cyan, purple, and white. You could do that with sRGB, and you can do that in AdobeRGB, or something else, the only difference being that in the larger colour space the primary colours will appear more brilliant. The concepts of bitdepth and colourspace are completely independent and you should always maximise bit-depth regardless of what space you're using.

The reason I'm still talking about other colour spaces is because Adobe by default will export from Lightroom, or import from Adobe CameraRAW in ProPhotoRGB, or AdobeRGB. 8bits per pixel is NOT enough to represent all visible shades in these spaces resulting in posterisation. So: For sRGB you can use 8bit or 16bit. For anything *other than* sRGB you should always use 16bit.

 

[Ysarex]

It's pretty clear from the OP's original question that he's using LR 4. LR's working color space is it's own special version of ProPhoto and that's the only color space LR lets you work in. LR saves all the library previews in Adobe 1998 and you have no option to change that either. So if the OP is using LR, as it seems he is, he's editing in ProPhoto and using Adobe 1998. If he's going to edit his photos using sRGB as a working color space he's going to have to get new software.

That's not entirely true. Lightroom works natively in MelissaRGB for all RAW files, whatever the current working profile is for all JPEGs, and softproofs all results to the Monitor colour space as reported by the operating system. In any case this is all academic as Lightroom doesn't give you the option to change the working bitdepth.

According to the people who designed the software that's not entirely true. Adobe refers to LR's working color space as "ProPhotoRGB" not MelissaRGB. They used to use the MelissaRGB description some versions ago but don't any longer. I said "it's own special version" because of LR's tone response curve that they apply along with the ProPhotoRGB color space. From Adobe's website: Adobe Photoshop Lightroom 4 * Color management

This is nit-picky terminology however and I do believe you and I entirely agree about best practice.

Joe

 

[TomBrooklyn]

I see. Thanks for the explanation.

 

[Garbz]

According to the people who designed the software that's not entirely true. Adobe refers to LR's working color space as "ProPhotoRGB" not MelissaRGB. They used to use the MelissaRGB description some versions ago but don't any longer. I said "it's own special version" because of LR's tone response curve that they apply along with the ProPhotoRGB color space. From Adobe's website: Adobe Photoshop Lightroom 4 * Color management

Sorry to follow up the nit-pickingness, but that link says nothing about the internal working profile of Lightroom. It mentions that the develop module DISPLAYS the image in ProPhotoRGB which is actually garbage since the develop module displays the image in the Monitor profile. Not surprised though since I have found the help pages on Adobe stupidly simplified at times. There was a great article on how Lightroom works internally on Adobe Labs pages before adobe gutted Labs of seemingly everything useful and had results removed from google (seriously adobe where is the 20 page guide on tweaking DNG profiles now?) But basically Lightroom processes in something resembling ProPhotoRGB with a gamma of 1. This is then converted to ProPhotoRGB with a gamma curve of sRGB and adds an offset as well and they called that MelissaRGB. MelissaRGB is used by any tool that doesn't use a linear gamma (e.g. noise reduction and histogram calculation) and is what is then converted to the Monitor profile for display when the develop module is open. This has actually annoyed a few people as the histogram in Lightroom (or ACR) may show clipping which then magically disappears when opened in Photoshop. Adobe Labs pages on this has disappeared but you can piece this together from the replies to various confused people on the Lightroom forums.

I'm not surprised they don't put this in the help files since it actually has very little impact on how anyone should use the Lightroom.