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Thread: Which colour space and bit depth?

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    Ausphotography Regular John King's Avatar
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    Which colour space and bit depth?

    This is a continuation of a discussion that has been taken way off topic in the original thread, here:

    http://www.ausphotography.net.au/for...51#post1352651

    Gidday Arthur and Kym

    Quote Originally Posted by John King View Post
    Gidday Kym

    aRGB monitors used to cost AUD$3-4,500 (Eizo ... ) for the last 4 years or so they have been under $1,000. Sometimes well under.

    There are very, very few commercial printers who even understand colour spaces IME, let alone use anything other than sRGB. This is why I do my own printing using an Epson R3880. This printer will reproduce most of a PPRGB gamut, and prints particularly accurate reds and yellows. Printing my own saves lots of differences of opinion, shall we say ... .

    Part of what I photograph is cars. These very frequently have colours that are well outside an sRGB colour space. Brilliant, vibrant reds which are terrific in ProPhotoRGB-16, and pretty acceptable in aRGB-16 turn into pinkish-orange in sRGB-16 or sRGB-8. Flowers are another case where the colour gamut and bit depth make the difference between very ordinary and excellent colour reproduction.

    If people are not particularly concerned with colour accuracy, I can understand why they are not particularly interested in wide gamut colour spaces or colour management generally. That's fine. However, I am particularly pedantic about colour accuracy, so have gone out of my way to implement a properly colour managed workflow.

    Regardless of how anyone approaches this subject, having a calibrated video card ("calibrated monitor") will always be beneficial, IMO.
    Quote Originally Posted by arthurking83 View Post
    I prefer not to keep a discussion off topic, but for the sake of clarity here:



    You've done(or doing !!) something wrong.

    If you're reds are not translating correctly in sRGB, then you have a problem with your workflow .. not sRGB.
    The problem is the sRGB colour space, Arthur. The problem with the colour mapping can easily be seen in ACR (on an aRGB monitor ... ) before any PP has been done to the image.

    I have taken the colour number readings from the same spot in the image posted below, with no post processing of any description. Open the RAW file in ACR, then change the assigned colour space from PPRGB to aRGB to sRGB and ColorMatch RGB (all 16 bit) and I get the following colour numbers - all listed as 8 bit colour numbers in R-G-B order:

    PPRGB - R = 151; G = 63; B = 39

    aRGB - R = 188; G = 27; B = 47

    sRGB - R = 221; G = 18; B = 42

    CMRGB - R = 197; G = 3; B = 30

    It is not difficult to see why these numbers will lead to significant colour shifts when printing. I stress again that this is with no PP of any description, merely changing the assigned colour space in ACR.

    Closing the image and re-opening using the target colour space and bit depth leads to the same result, so ACR is not re-processing the image in any way, and besides, ACR doesn't work that way.

    All the other discussion and reasons you have advanced are not relevant, as no PP has even been done to the image at this stage.

    This is the image. It has been converted to sRGB-8 for web display. The point measured is to the right and down from a small spot of sap shown larger and circled in the second image.





    Note that placement of this point can be reliably replicated by placing the ACR magnifying glass with cross hairs such that the 10 o'clock position of the cursor just touches the sap spot.

    I have printed this image dozens of times (about 25, IIRC ... ), using all the permutations and combinations of colour parameters and without any other editing whatsoever. The differences between the results are stark, and do not require turning the print over to see what colour space and other parameters were used.

    If you had a problem in your greens, then it could be understandable that you're having green colour issues.

    But from a technical standpoint, the difference in the red and blue channels between sRGB and aRGB are insignificant enough that there is no difference.
    RGB colours are made up of a mix of the R,G, and B colour numbers. While these should be shown as 16 bit colour numbers, I find these far less intuitive than using 8 bit colour numbers for reference purposes in ACR. I use 16 bit colour numbers for my web site colours, and it is more than just painful! The precise mix will alter the final colour. The colour numbers quoted above indicate a very large shift in the colour of that spot on the image given as an example. I have measured many, many points on this image (and many others), before arriving at my conclusions and my work parameters. I actually do almost no PP to my images ...

    Where aRGB extends beyond the bounds of sRGB's ability to reproduce colours is really only in the green channel(a quick look at those colourspace triangles will confirm this!
    See above re the mix of colour numbers.

    I've done both and have used both, and the printer(company) I've used has advised me on what colourspace to use for the appropriate situation.
    He's happy to print 'accurately' in sRGB, but does recommend to use aRGB .. which is more a a precautionary method to print colours nicer.
    I once had a large image that we assessed that would print best if set to the aRGB space .. even tho I shot the image in sRGB, but this print had a lot of green(dark green grassy) areas.

    On no other image I've presented to him has he commented that it needed aRGB .. but I did so simply to maintain a standard workflow.
    That is, my workflow for this printing company is to edit the images I've getting them to print will always be set in aRGB.
    So you are already using aRGB, not sRGB, for printing?

    Kym's comments are a very important aspect .. don't convolute your workflow unnecessarily, which can produce worse results than you're trying to achieve!


    And to reiterate(again) the discussion on colourspace here is not within the scope of assisting the OP!
    It is when she has posted images with an aRGB colour space on the web.

    Quote Originally Posted by Kym View Post
    Which confirms my point exactly. A small almost undetectable benefit for a more complex workflow and more cost.
    KISS is still a very important principal.
    1) the difference is not undetectable to me, not by a considerable margin. That is, it is considerably more than being a 'just noticeable difference', or JND.

    2) As to expense, a decent P-IPS monitor costs about the same as a 1.4x teleconverter. It provides many benefits other than "just" displaying an aRGB colour space - viewing angle, even illumination, portrait/landscape modes, height and angle adjustable stand - that cheaper montiors usually do not provide. The Asus PA246Q monitors I bought also provide a deeper bit depth - 12 bit colour lookup table (LUT) with a 10 bit panel, if connected using either a dual DVI or HDMI connection to the video card.

    A much more important investment is having a calibrated monitor.
    Agreed. This is extremely important regardless of colour space or bit depth used. However, it is not a zero sum game ... One needs to have a good quality monitor, AND one needs to calibrate one's video card. Both are very important.

    As AK said if your reds are an issue I'd be looking elsewhere for a solution.
    My reds (and lots of other colours ... ) are not an issue when I use a PPRGB-16 colour space. As I have written before, aRGB-16 is the safest colour space; PPRGB-16 is the best colour space - IMO.

    I note that much of the photography here is of either birds or landscapes. While I have an interest in these genres, my photography ranges over a far wider scope than these two subjects. Many of the things I photograph contain man made materials, and many these have far wider colour gamuts than the natural world (as a very, very general rule ... One has only to look at the colour gamut perceptible to either a dragon fly or a mantis shrimp to understand that the natural world has a very broad colour gamut indeed!).

    I want to be able to reproduce those colours accurately, and my un-convoluted work flow does that very well, and has done so for many years. My touchstone of colour accuracy is to compare the print with the real world object in as close to the original lighting conditions as possible.

    If anyone is perfectly happy with using an sRGB colour space, far be it from me to proselytize them about switching to what suits me and my photographic aims.

    sRGB will not reproduce the colours that match the real object in the real world. Neither will aRGB or PPRGB, but they come a great deal closer to this than does sRGB. Let's not talk about ColorMatch RGB, it is a bad joke.
    Last edited by John King; 16-04-2016 at 12:27pm. Reason: corrected typo in colour number table
    Regards, john

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  2. #2
    Ausphotography irregular Mark L's Avatar
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    Thanks for that John.
    For what I use my photos for I don't think tere would be a huge difference in the final outcome for me. Have just purchased a a new printer so might try a few things you mention, eventually.

    Quote Originally Posted by John King View Post
    Many of the things I photograph contain man made materials, and many these have far wider colour gamuts than the natural world (as a very, very general rule ...
    Another thread for another place maybe.

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    Gidday Mark

    Glad to be of some help in this very complex topic.

    The reason that I shoot aRGB for OoC JPEGs is that very little will be changed if remapping to an sRGB colour space. I wrote a PS action many years ago that does this as part of an automated process to prepare OoC JPEGs for the web (etc). However, going in the other direction is impossible. It is always possible to map a larger colour space to a smaller one, but not the other way around. How this remapping is done is a subject all by itself.

    There are only certain images that will be considerably or dramatically different in wider gamut colour spaces. Highly saturated reds and yellows cannot be represented accurately in an aRGB colour space, but can be in a PPRGB gamut. Both of these types of colours commonly occur in both flowers and cars, among other things. Using PPRGB-16 certainly adds vibrancy to the prints when these colours are present ...

    My monitor cannot display these colours, being limited to aRGB. However, my Epson R3880 can print them. The inability of current commercially available monitors to display a PPRGB colour space is a drawback if one does colour edits on images. I don't (99.99% of the time ... ). Changing WB values is technically a colour edit, but is not really, as a RAW file doesn't have a WB (or a colour profile) until one is assigned during raw development.

    I look forward to full 16 bit, PPRGB monitors. They might yet appear in what remains of my lifetime .

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    A royal pain in the bum! arthurking83's Avatar
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    Quote Originally Posted by John King View Post
    ......

    Open the RAW file in ACR, then change the assigned colour space from PPRGB to aRGB to sRGB and ColorMatch RGB (all 16 bit) and I get the following colour numbers - all listed as 8 bit colour numbers in R-G-B order:

    PPRGB - R = 151; G = 63; B = 39

    aRGB - R = 188; G = 27; B = 47

    sRGB - R = 221; G = 18; B = 42

    CMRGB - R = 197; G = 3; B = 30

    It is not difficult to see why these numbers will lead to significant colour shifts when printing. I stress again that this is with no PP of any description, merely changing the assigned colour space in ACR.

    .....
    One point I'd like to make here, as it points to an understanding that may not be as complete as it could be(and to be clear, there is no disrespect intended!!).

    Just because the RGB levels have changed, doesn't immediately imply that there is a colour shift!
    The key is the colourspace that has been set. Setting the colourspace WILL change the RGB points, as that's the point of colourspace designation.
    You've confused what colourspace and RGB levels are doing here .. basically undersimplified(if that's even a word!? ) it.

    You can't isolate the RGB values of aRGB and sRGB the way you have there simply by comparing them in that manner.

    if your R(red) level in aRGB = 188 then the R(red) level in sRGB must = 221 simply because that's what the change in colourspace needs to be. This doesn't mean that there is a colour shift!
    For many people this is a hard concept to grasp, and why they shy away from learning what colourspace is all about.

    The reality is that it's not so difficult to understand, as long as it's not convoluted or misused.
    The in the above quote, it's been misused!

    If you take it at face value then yes, there seems to be a colour shift because you're simply comparing numbers.
    But what hasn't been mentioned or accounted for is the difference in what RGB actually means for each of those colourspaces listed.

    RGB values for each of those colourspaces is not the same thing. They rely on another aspect called chromacity. It's a tech issue that most folks simply don't want to complicate their lives with, but it's important in that those chromacity values determine what each RGB value will be.
    So to say that the values [R 188, G 27 ,B 47 in aRGB] is a colour shift when compared to [sRGB R221, G18, B42] is not true. They are simply two different translations which equate to the same colour ... with the caveat that the colourspace translation hasn't been incorrectly applied at any point in the workflow chain.
    And there's the problem .. the workflow chain .. from start to finish. Everyone has a different start and finish point so that no one single workflow is the right one.

    In your example: the inaccurate red shift you see in your final sRGB image isn't because of the change to sRGB or aRGB, although the theory of colourspaces should dictate that reds will translate the same way.
    The issue could simply be that you're working in PpRGB colourspace. PpRGB has a red colour space that is larger than both aRGB and sRGB(remember that the red channel in sRGB and aRGB are the same).
    It's easy to assume that you're monitor is aRGB capable, but it should be noted that it's most likely not 100% aRGB capable. I think there are a very few uber high end screens capable of 100% aRGB rendering, but these are the multi $K types. The high end average consumer screens are basically all some slightly lower percentage aRGB capable(between 99-97% accurate).
    What's not pointed out is that in which colour channel that accuracy is quoted for? ie. is it 98% accurate for the R channel, or G channel .... or is it for all three colour channels?
    It's definitely not PpRGB capable that's for sure .. yet many folks insist on working in this uber ProphotoRGB colourspace!(to me it makes no sense!!)
    You're working in a colourspace that can't be 'accurately' rendered, so as you do work you're not seeing what you're actually doing.
    Like Kym said ... KISS!

    On a similar note, what not many people realise is that they set themselves up for a full aRGB workflow with a higher end aRGB(ie. 10 bit) screen, but never take into account if the graphics card is actually 10 bit capable, or if the OS has been set to 10bit rendering mode.
    Did you know that it was only with a recent update(maybe a few months ago) that Apple finally allowed true 10bit colour ability in the Mac OS?
    Many folks thought they were working in aRGB mode, where the reality was they actually weren't!
    I've tried to research as many graphics cards to see which do 10bit and which don't, but there's not much real info available.
    From what I've found, if you want 10bit capability, you're best off with a Radeon card(as it's more likely that they do), and do a lot of delving before you commit to an nVidia card!
    Using a HDMI or DP cable is in no way certainty that your graphics card is outputting 10 bit colour.
    You're screen may lull you into thinking that you are now in 10 bit mode, but screens are dumb! They have no idea on what the device driving them is. Graphics cards and OSes are the 'smarts' that do all the communication.

    viewing aRGB isn't a matter of just plugging in your new 10 bit monitor and off you go!

    The earlier reference to the total workflow from start to finish. From my understanding of what you do John, I assume that you've profiled your printer for each batch and type of paper used for any given instance of print?
    If not, then there's one more link in the chain to go wrong.

    The reason I use sRGB is simple .. KISS! Like Kym said(again, and only because it's important!!!!) .. if you allow your workflow to introduce errors into your system, even as low as 1% ... those 1%'s add up to a significant margin for error. And if criticality is an important consideration, then when you don't have an understanding of what and where those errors are, then you just end up chasing your tail forever.

    I'm the same as you in the sense that I try not to tell people what to do with their time and space!!
    All I try to offer is advice: that if you convolute your processes, then you end up in that spiral of chasing tails as per above.
    While I don't (yet) have an aRGB capable monitor, for a while I thought it was important, only to research that it actually isn't.
    I will update soon tho, and even when I do, I will still stick with the sRGB workflow for most of the time. I rarely print my images(much less than .01%!!) for those times when the printing mob say .. " ... yeah, better do this one in aRGB to be sure" I probably will.

    of the printing that I have done, the vast majority has been in sRGB, but this is misleading to a degree. I had a batch lot of 100-200 images I had printed for my mum, many were scans of her old photos, but she also wanted some of my (digital)photos over the past 10 years. The entire lot was done in one hit .. all sRGB. At that time I also had a test print made in a larger size(basically A4) also in sRGB. I use that large print as my final calibration point for my screen, after I calibrate it.
    That is, no point in calibrating a screen but not referencing it to a fixed point too! While I don't regularly print, I do see print as the final fixed point in the workflow.
    Of all the other(5-10, I think) large aRGB prints I've done(all for other mind you) .. (once again) after I get them home, I reference them against the digital images on screen too.
    So while the aRGB print has been specifically set to aRGB for a controlled quality purpose .. referencing it to my lowly sRGB monitor reveals no difference(other than expected illumination differences) to the aRGB print.

    But one thing I do agree with you is using aRGB colourspace if you shoot in jpg mode.
    That makes perfectly good sense simply due to the fixed nature of jpg(and tiff too .. but no one in their right mind would shoot in tiff mode in the camera).
    ** as side note, my far fetched hope is that camera makers would one day come to their senses and drop tiff mode and replace it with a solid open standards image format .. kind'a like DNG is supposed to be**

    Because this reply was so long, I didn't want to touch the topic of colour of so called 'real world objects' .. I'll do so in another reply. Suffice it to say that the so called advantage of ProPhotoRGB in displaying 100% of real world colours is not really what it appears to be.
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    Ausphotography Regular
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    Quote Originally Posted by Mark L View Post
    Have just purchased a a new printer so might try a few things you mention, eventually.


    Gidday Mark

    What make and model is your new printer, mate?
    I thought of asking you this about 60 seconds after I had put all my computers to bed for the night last night. It's always the way with me .

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    Quote Originally Posted by arthurking83 View Post
    One point I'd like to make here, as it points to an understanding that may not be as complete as it could be(and to be clear, there is no disrespect intended!!).
    Gidday Arthur

    I'm not ignoring your post ... .

    There is an awful lot happening here ATM, and it will probably be at least mid-week before I have time to turn my mind to what you have said.

    FTM, suffice it to say that I suspect that we are approaching this question from totally different directions. I am trying to work out why one colour space delivers the goods for me, and why another doesn't. There is no element of theory in what I am saying. Prints from PPRGB-16 give terrific results that have a high correspondence with the real world objects being photographed, regardless of what they might be. Prints from sRGB-16 or sRGB-8 do not.

    Will reply when I can, further down the track. We have had a death in the family. My wife is the executor, and the deceased's affairs were a disaster area. She is in the middle of her final subject for her Fine Arts degree ... All systems are go here - except for my weary body and mind ... .

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    Ausphotography irregular Mark L's Avatar
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    Quote Originally Posted by John King View Post
    Gidday Mark

    What make and model is your new printer, mate?
    A basic Brother MJC-880DW since you ask.
    No need to comment given other stuff.l

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    So if you have an issue with the sRGB colour space. why are you using it?
    "It is one thing to make a picture of what a person looks like, it is another thing to make a portrait of who they are" - Paul Caponigro

    Constructive Critique of my photographs is always appreciated
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    Gidday Rick

    I don't use sRGB, and never have, except for converting to that colour space for web use, or when sending images to others for their use (safest for unknown end use ... ).

    I have done extensive experiments to ensure that I'm not talking through the other end of my alimentary canal ...

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