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Thread: Subject for tutorial or discussion?

  1. #1
    Moderator Donald's Avatar
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    Subject for tutorial or discussion?

    In this thread, Colin has written:
    ... however in post processing you'll usually have to stretch the tonal range by a stop or two because monitors can display around 5 or 6 stops of dynamic range (more than paper) which is why images require different treatment for printing -v- display on a monitor (and a large part of why images on the screen will NEVER look exactly the same when printed).
    This is one of those subjects that I find both mystifying and terrifying and is probably the reason I've never got into printing (either myself or paying for it from someone else).

    I don't know enough to know what questions I have, but it's something along the lines of - How do you prepare something on screen to know that it'll come out okay on paper?

    What do you think?

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    Re: Subject for tutorial or discussion?

    Donald, I'm right up your creek here. I have a quite nice Canon iPsomething printer, but never seem to get prints of it that match the monitor. I keep moaning about it and people keep saying "You need a calibrator" Well, tech stuff like that is a challenge and so far I've managed to put said challenge off, but just yesterday, I bought on on TradeMe at a price that I couldn't refuse, and now I'm gnawing ma knuckes wondering if it is just going to be a hunk of technology that I can't deal with. In short...ha ha... I'd like a tute and a discussion... greedy ole me.

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    Re: Subject for tutorial or discussion?

    I'd certainly like to see a tutorial about it. From what I've seen and done so far, I'm afraid there will be few absolute answers, and lots of "it depends" on the circumstances of image and output device. But that's true of some other things, like sharpening, and even the exposure triangle. A framework for how to think about the process would be really valuable. I use Spyder for my monitors, which is okay, but for output, I'm pretty much guessing based on what's worked (and mostly, failed) before.

    Cheers,
    Rick

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    The Blue Boy's Avatar
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    Re: Subject for tutorial or discussion?

    It'll certainly be interesting to see what Sean, Colin or Dave will have to say about this. I think they will mention colour space being used in post, i.e. for printing, proof it in CMYK mode. A tutorial from Sean gets my vote though!

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    Re: Subject for tutorial or discussion?

    I'm with you guys.Haven't done much printing myself.I use Spyder3 to calibrate my monitor.Not a difficult device to use.I don't have my printer(HP C8180)calibrated.

    I've tried different processes.Let Elements manage the colour,let the printer manage the colour and I can't see any difference.
    I will say,definitely calibrate your monitor.It does make a difference.
    I can produce very good 8.5 X 11 prints with my setup.
    Image sharpening techniques for output,to me,seem to be fairly important.
    Rick said it.It depends on what you want to do with the image.

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    Re: Subject for tutorial or discussion?

    I have an hp photoprinter and if I use the defaut settings (on photo paper) I get adequate output, but when I increase the amount of ink used, I usually get good comparative prints to what I see on the monitor. You do have to tweak the settings and remember, photos aren't really meant to be viewed up close. The closer you look the more imperfections you will see. and of course, a good resolution image, free of OOF, makes the difference.

    Quote Originally Posted by Klickit View Post
    Donald, I'm right up your creek here. I have a quite nice Canon iPsomething printer, but never seem to get prints of it that match the monitor. I keep moaning about it and people keep saying "You need a calibrator" Well, tech stuff like that is a challenge and so far I've managed to put said challenge off, but just yesterday, I bought on on TradeMe at a price that I couldn't refuse, and now I'm gnawing ma knuckes wondering if it is just going to be a hunk of technology that I can't deal with. In short...ha ha... I'd like a tute and a discussion... greedy ole me.

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    Re: Subject for tutorial or discussion?

    Hi Guys,

    It's really not too hard, although having just said that I'd better now think of a good analogy to make it all seem simple ...

    Writers block, darn!

    Just kidding

    OK - just a few foundations first ... I mentioned in a post to Dave a couple of days ago that there's really no such thing as a "black" anything (with the single exception of a Black Hole). If there were then we wouldn't be able to see it, no matter how much light we threw at it. So the first concept we have to get our head around is that even things that we normally think of as being black still reflect a fair bit of light as do objects that we're more used to thinking as being highly reflective, such as the colour white.

    So in terms of what's printed on a piece of paper (say for the sake of the discussion a black square - a white square - and a medium gray square) if we were to start talking about how much light does the white square reflect compared to the black square (eg contrast ratio) then the initial thought of many is "a really big number" since the white square will obviously reflect "something" and the popular notion is that the black square won't reflect anything - and anything divided by nothing (or next to nothing) gives a really big number - but - that's not the case ...

    As photographers we're used to dealing with stops - and somewhat surprisingly - the difference between black and white printed objects is typically only around 4 stops. Yes - you CAN get special high-performance high Dmax inks, but they're beyond the scope of what we're discussing here - so when printing you typically have to squeeze your entire tonal range into 4 stops. Monitors on the other hand - due to their active light source - can typically achive a useful contrast ratio of around 6 stops (forget manufacturers gabillion to one contrast ratios - whilst they might be technically correct they have no relevance in the real world).

    So if you take a shot in RAW (capturing around 12 stops of info) you typically only see the brightest 6 unless you use something like a fill light control to raise the level of some of the shadow detail that's been captured, but is too dark to be displayed. So in essence RAW conversion becomes a case of choosing which 6 of the 12 stops of dynamic range you want to display by adjusting the sliders. When we print we're typically taking our 6 stops of info that we see on the screen and compressing ("rendering") it down to 4 that we print. If the end points remain the same (ie monitor white = paper white and monitor black = paper black) then everything else inbetween gets compressed - often it compresses OK, but at other times it changes things in a way we don't like; colours in particular are very sensitive to brightness level (that's why a sky will look a LOT more saturated if you under-expose it by a couple of stops).

    The rules the programs follow in converting between devices of different capabilities are called rendering intents - and you can tell it to use 1 of 4 that (hopefully) best suits you needs - but often despite all the good theory, the bottom line is that because monitors are an additive RGB technology and printers are a subtractive CMYK technology (even though they may have an RGB interface - needing yet ANOTHER conversion) - with different dynamic range capabilities as explained above - it's just a fact of life that they don't convert seamlessly - and as a result prints matching the screen rates right up there with Santa Claus and the tooth fairy; Great concept, but the reality is something different!

    So what to do about it ...

    In reality it's not that hard because there is only so much you can do and a lot you can't ... and there's no point worrying about what you can't fix. What you CAN do is work from a calibrated and profiled screen that will get the screen working to a known standard - and then print to a profiled printer so that the printer is printing to a known standard. Of course some will get OK results without going through this process - but saying that "their colours match" etc is very subjective (what they call OK I might have nightmares over) - and of course depending on the image the results they get may be wildly inconsistent (eg one colour on the screen might under-saturate - a printer might over-saturate and the net result is normal - but - another colour might over-saturate on both devices and give a horrible result). So if people want to do colour management on a wing and a prayer then good luck - but if you're doing (or trying to do) professional-grade work especially portraiture that require accurate skin tones) then having the right gear is going to make life a lot easier. It doesn't mean to say that you still won't have to adjust the image - but you'll have then eliminated a couple of the variables to make the outcome far less of a lottery.

    In terms of "real world" results I can tell you that experience helps a lot - I know that when I'm printing on canvas I need to clip the histogram at around 8 to 16 at the low end, and around 238 at the high end - and often I can get it in one print - other times (case in point the print I'm doing for Agata) there can be colour shifts in areas of the print that simply do not appear to be present on the screen - and one just has to work around them.

    So the bottom line when printing is - calibrate & profile screen - profile printer - understand colour management - use your experience - and then make the best decisions you can to produce the required result in as few a test prints as possible. In terms of a magic solution that always prints exactly what's on the screen ... forget it ... it's ain't ever going to happen every time.

    Hope this helps!

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    Re: Subject for tutorial or discussion?

    Thanks, Colin!! This is a lot of information, and helps cover the whole processing chain.

    It seems that each step in the process is a reduction in dynamic range. The eye sees 24 stops, camera raw records 12 stops, the monitor shows 6 stops, and the printer prints 4. But the end result is for the 24-stop human eye to look at it and be seduced into imagining the original scene. I know the 24 stops of the eye are dynamic, but people's perception doesn't necessarily know that: like DOF.

    We're tone mapping all along the way. Just like "protect tones" in dodge or burn, we hope to keep the perception of color intact as we do that, right? Is that the key? Can we consider the tone mapping the issue, work in the printer's RGB interface, and trust the color mapping algorithms to be true? Or do we need to shift to CMYK (or Lab?) while we're still in a 6-stop world, so that we tone-map in a consistent color space?

    Cheers!
    Rick

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    Re: Subject for tutorial or discussion?

    Quote Originally Posted by rick55 View Post
    Can we consider the tone mapping the issue, work in the printer's RGB interface, and trust the color mapping algorithms to be true? Or do we need to shift to CMYK (or Lab?) while we're still in a 6-stop world, so that we tone-map in a consistent color space?
    Sometimes CMYK or RGB or LAB will isolate a particular type of information better than the other for processing - but to be honest I just use RGB a lot for normal images - I use LAB when there's something I want better colour control over or if I need to do more agressive sharpening (ie on problem images) - and I never use CMYK for anything (keep in mind that even though the printer is CMYK inks the monitor is still limited to an RGB gamut, and is still an RGB device -- as such I've just never found any compelling reason to use CMYK).

    Having just said that, LAB is really my "first love" - it's just that many images (if shot correctly) don't need a lot (or any) colour correction outside of the RAW converter - so I end up leaving the image in the RGB default).

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    Moderator Donald's Avatar
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    Re: Subject for tutorial or discussion?

    Quote Originally Posted by Colin Southern View Post
    Hope this helps!
    As always - wonderful. Now I understand what it's about. A candidate for the 'really-helpful-threads' list - except I can never remember how to find that!
    Last edited by Donald; 25th May 2010 at 05:58 AM.

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    Re: Subject for tutorial or discussion?

    Quote Originally Posted by Donald View Post
    . A candidate for the 'really-helpful-threads' list - except I can never remember how to find that!
    I can help with that too

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