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Thread: Histogram Colours ect

  1. #1

    Histogram Colours ect

    I struggle to achieve close enough true colors straight from camera(I take photos of fabric) you will probably know why when you read the rest. There are lots of theories on WB and metering and use of histograms but to be honest I somehow miss the point of it all. If our camera meters for 18% grey all the time (spot or partial metering I do not use other types ) and use the zone system or a grey card as our guide is this the reference point for the histogram if not what exactly is reference point for a histogram. If the histogram is only a result of our exposure settings and has no reference to the mattering system directly then we are left to search for correct WB and 18% grey ourselves. And how does this then translate to the fact that the colors change depending on the intensity of light reflected from them when we use flash for example. If we could get 18% grey in the middle of our histogram at least we would have ref point and new where we are in our dynamic range. I sort of understand that lighting conditions are crucial but even when light is good taking a photo of a grey card it takes a lot of messing about to get it in the middle of the histogram (then everything looks wrong anyway) or even better taking a photo of a white and a black card together will almost never end up at the opposite sides of the histogram but mostly fairly near each other(unless we flash it to death) so what is histogram all really about and it is worth researching any further.

  2. #2
    DanK's Avatar
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    Re: Histogram Colours ect

    Robert,

    I think you are confusing a bunch of different things: exposure, white balance, other aspects of color, and tonal range.

    One use of a neutral gray card is to set exposure. The camera's meter will take some area of the image--which area, and how weighted,depends on the metering setting--and set the camera's exposure on the assumption that this area is 18%. If the area is brighter or darker than that, the camera will under or overexpose. A neutral gray card is one way to avoid that problem.

    A second use of a neutral gray card is to set white balance--in essence, to set the color temperature. Here again, your camera guesses if you don't use a card. If you have a properly exposed gray card, you can set white balance correctly in postprocessing, regardless of what the camera guesses.

    Re hitting the ends of the histogram: that depends on the tonal range of the image, which in turn depends on both what the image is and what the lighting is. For example, on a gray day, tonal range is often fairly narrow. Using a gray card has nothing to do with this. You can adjust it at will in postprocessing.

    Re other aspects of color: of course, they will change with lighting conditions. For example, even after correcting white balance, you will get a different mix of colors in bright sunlight than in cloudy conditions. You can adjust this in postprocessing too, but it is more complicated than adjusting tonal range.

    Finally, re this:
    I struggle to achieve close enough true colors straight from camera
    I think you may be misunderstanding what 'straight of of the camera' (SOOC) is. A digital image, just like a film image, needs to be processed or developed. If you take the image SOOC, you are doing the analog of dropping film at the drugstore and letting them make prints. In essence, you are selecting a developing algorithm in advance (for example, selecting a picture style and white balance) and telling the camera to develop the image that way, no matter what characteristics the original image has. Sometimes that will work, but often it doesn't. You are much more likely to get what you want if you learn to do at least basic postprocessing yourself.

    Dan

  3. #3

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    Re: Histogram Colours ect

    I am afraid DanK's assumptions about the usage of a grey card are flawed. I too had that childish faith in the grey card until I could erase it completely from my mind forever.

    Grey cards are not for evaluating colour. Most "grey cards" are in fact not grey at all. For critical colour evaluation, you need a spectrally neutral target, like the WhiBal card. If you don't have one, there are some substitutes that work and several that don't. Among the substitutes that don't work are white paper and most of the grey cards in the market. So your observation that everything gets wrong when you use a grey card for setting white balance is quite in order. With a grey card as WB target, your colours should be off.

    One cheap substitute is bleached paper pulp, as long as no whitener is added to it. That includes many household papers and sanitary papers that do not contain whitener. They appear a bit greyish when you look at them, but they are very close to neutral, and they are far closer to neutral than for example a Kodak grey card, whether its grey or white side is used. The drawback with toilet paper is that it is rather fragile, gets dirty easily, and soaks up water. The positive side is that it is dirt cheap, just tear off another piece.

    Now back to the grey card. It can be used for evaluating exposure, and the Kodak grey card should fall in the middle of the histogram, while some other grey cards should fall lower. The WhiBal card is not for evaluating exposure, it will fall within Zone VII or VIII when correctly exposed. It is not intended for exposure evaluation, but for colour. It is purposely brighter than a grey card in order to obtain sufficient data for White Balance calibration. But any grey card will show three different spikes close to the middle of the histogram, one blue, one green and one red. That is because grey cards are not grey, they are not free of colour, they do not reflect all colours to the same degree.

    If you really would like to check the light on your subject, you'll do better using a meter that does not measure luminance, but illuminance. There are cheap illuminance meters in the market that are perfectly suitable for the task, or you can use any good exposure meter that can measure incident light, the light falling upon the subject. If you use a scientific luxmeter, you will need a conversion table for your camera, to get the corresponding exposure, while for the exposure meters, it suffices to set the correct ISO that would correspond to the ISO of your camera; mind that these two ISO numbers may not be the same. Cameras and meters may deviate from the correct values and do so.

    Once you get a good standard method for your work, you may use the same method each time.

    There is a caveat to colour correction, and it is the fact that eyes and cameras don't see exactly the same thing. Camera engineers have gone to great length to find filters and sensitivities that correspond to the spectral response of the three different types of cells in the eye that respond to colour, but it is not perfect, and differences in colour are known as Metamerism. We can see it from the colour gamut of the photographic system and its colour spaces. While the eye usually can cover a larger colour space than any photographic system, we resort to standards regarding colour spaces and gamuts, in order not to make life too hard. You will also find that colours are not the same when using daylight or incandescent light, and that the "colour temperature" is not the only determining factor when setting white balance. The spectral curves of incandescent versus daylight are greatly different, and the Ra-numbers of colour temperatures rely on different spectral curves when the light source is under 5000K than when it is 5000K and over. Incandescent bulbs may be corrected for this difference with a neodymium filter, and in that case, their Ra-value drops to 60+ although they provide better colour for photography when compared to daylight: the neodymium filter cancels out some of the metameric differences.

    So if you're into the colours of fabrics, you need to learn all those things and work with them. One first step might be going to the WhiBal website and look at the videos, and then order your WhiBal card that lasts forever or substitute with a toilet roll of bleached but unwhitened paper. The WhiBal card is a safer bet, as it is meticulously made and tested to be spectrally neutral. It's a good starting point.
    Last edited by Inkanyezi; 21st June 2012 at 12:55 PM.

  4. #4
    DanK's Avatar
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    Re: Histogram Colours ect

    Urban,

    To avoid confusion: I think there is some inconsistency in terminology, and the term "gray card" is used for different things. whiBal (marketed as a "the best digital Gray Card available anywhere") is what I use, and as you note, it is intended to set white balance.

    However, you are correct that that particular gray card is not 18% gray by design. I did not know that. I use the histogram for exposure, not my whiBal, so I never thought to check. That's a very useful thing to know, and I am glad you pointed it out. Here is their statement about this:

    The WhiBal is not 12% or 18% gray by design. It is light gray because we can get a better White Balance this way. The darker the Gray, the less steps there are by which the software can adjust the White Balance. The WhiBal is not designed or represented as an exposure tool. There is also great debate as to whether 18% or 12% or something in-between is the proper value.
    Dan

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    Re: Histogram Colours ect

    I agree completely with you Dan. There is far too much confusion in the photographic field. And I got really mad when I found out that it is impossible to use a "grey card" for WB. I thought they were made to be spectrally neutral, but I was deceived. The WhiBal is a very good target for the WB shot, and when you save your images RAW, it is the simplest way to get everything correct from start.

    Urban

  6. #6
    Administrator Manfred M's Avatar
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    Re: Histogram Colours ect

    I’m not quite sure as to where to start. The previous posting covered off some good discussions regarding white balance and proper exposure, but I don’t think they have exactly answered your question. Colour management is a whole topic on its own, and I certainly do not claim to be an expert here, but do have more than a rudimentary understanding of it.

    First of all, I am assuming that you are viewing jpg images out of your camera when you make that comment. A jpg is a processed image that uses settings you have put into the camera, as well as algorithms that the camera manufacturer has programmed. This could be the starting point of why what you see is not what you get. Shooting RAW would remove these variables, but you would then have to make the appropriate adjustments in post-production to get the right results too. You might want to consider shooting a test target; I use the (now discontinued) x-rite mini-colorchecker card to baseline my colours and that way I can do accurate adjustments in post production.

    Other considerations; your shooting lighting conditions; even if you white balance could be part of the issue. Every different light source has its own quirks. Fluorescent lights, especially cool white, are deficient in warm tones. Tungsten light is good for warm tones, but is not great for cool tones. Your eyes and brain will make things “look right”, but your camera sees things as they are, so this could be part of your issue. Colour casts can be introduced by the place where you are shooting (shoot in a room that is painted, say dark green), mixed lighting (a combation of daylight coming through a window in a room that is lit by tungsten light). If your colour balance point is not identical to your shooting point, you could be introducing conditions your colour balancing missed.

    If you are looking at the images on a computer screen, it needs to be calibrated to give you proper colour rendition, and even there, especially if you are using a low end screen, your colour accuracy will be off.

    If you are printing, you have to use the appropriate colour (ICC) profile for the printer and paper you are using, otherwise colours will be off. If you are viewing a print in light that is not balanced (same scenario that I pointed out in lighting during your shot), the colours will look off.

    These are just a few of the variables that could be causing the issues you have asked about.

  7. #7

    Re: Histogram Colours ect

    Hi Dan

    Thank you for your replay and your comments
    I think that more research on my part is required and it is true that some confusion is present but I am keen on finding out what’s what – a camera is only a machine that is guided by a few basic parameters in an image – hence I mentioned a need for a recognizable and controlled reference point which would help me understanding the results. I accept that post processing is a very important part of it all and I know that a lot can be achieved with a raw file and I do use both raw files and some post processing to better my results.
    Regards Robert

  8. #8

    Re: Histogram Colours ect

    Hi Urban

    Thank you for your replay it is very encouraging to see that other people too are fighting the same enemy – I find your comments most helpful and will definitely take a very close look the your suggestions
    Regards Robert

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    Re: Histogram Colours ect

    The colour space that you are working in will also have an impact on how close the colours are to the correct colour and of course whether the monitor has been calibrated so that you are seeing them correctly.

    These two images have been processed the same except for the colour space. One is in sRGB and the other in Adobe1998. Otherwise they are the same.

    Cheryl

    Histogram Colours ect

    Histogram Colours ect
    Last edited by Cheryl Davidson; 22nd June 2012 at 10:15 AM.

  10. #10

    Re: Histogram Colours ect

    Hi Manfred

    Thank you for your comments

    I would like just to confirm that I do not look at the images out of my camera but look at the histogram and the raw files and this is what I meant by “out of camera” . I have been looking to acquire an X-rite passport and will do in the future but not until I am happy with the way I use my grey card(or a reference card) to set up my WB and my Exposure . I use a budget 24 inch screen which has been calibrated by a Spyder and will upgrade monitor one day soon. I need to have a good look at my lighting conditions and do more tests - I use white background and mixture of ambient (80%daylight and 20%florescent) and flash. The idea is to insulate every individual piece of the jigsaw and see the best way to control it – I am still fighting with histogram and trying to see how to draw the maximum out of it . Regards Robert

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    Hi Robert,

    A correct exposure will only get you so far.

    A reflective object only has a dynamic range of about 4 stops - most monitors will display around 6 - and most cameras will capture around 12 (but only show the top 5 or 6 on the in-camera histogram).

    This means that in essence "something has to give" ...

    If you get a middle gray to expose in the middle if the histogram then a reflected white will be 2 stops above that - but - the cameras will be able to record about 1 stop above that point - so it won't be a pure white as far as the camera and monitor are concerned.

    If you try to "get smart" and apply 1 stop of exposure compensation at time of capture so that the white is captured as a true highlight then - unfortunately - this also shifts the blacks up a stop as well, and what would have been a black - at 2 stops below middle gray - becomes only 1 stop (ie a reasonably dark gray, not a true black).

    So if you're displaying on a monitor then you MUST stretch the tonal range of the image from the 4 stops (maximum) that cover the reflective object into the (typically) 6 stops that a monitor displays so that both your highlight & shadow points correspond.

    If you don't then you'll have a tonal range offset, and that in turn will affect the perception of the colours.

    The second issue you'll have is with colour calibration. It's great that you're working from a profiled monitor, but the accuracy you're seeing is only as accurate as the profile that converts the camera's capture into the image that's presented to the monitor. In other words, if you're serious about colour management then you need to get that Color Passport ASAP. Think of it as a profile to correct for the camera/conversion inaccuracies much like the monitor profile corrects for monitor/display adaptor inaccuracies.

    The third issue is your lighting. Cameras have different response characteristics to the human eye - and using mixed lighting like you are is a bit like running your car on petrol ... with a little bit of diesel mixed in and a bit of oil mixed in for good luck too: In theory it'll handle it, but in practice, the performance won't be as good as if you stuck to just petrol.

    Hope this helps

  12. #12

    Re: Histogram Colours ect

    Quote Originally Posted by Cheryl Davidson View Post
    The colour space that you are working in will also have an impact on how close the colours are to the correct colour and of course whether the monitor has been calibrated so that you are seeing them correctly.

    These two images have been processed the same except for the colour space. One is in sRGB and the other in Adobe1998. Otherwise they are the same.

    Cheryl

    Histogram Colours ect

    Histogram Colours ect
    Hi Cheryl

    Thank you for your comment - I have already come across the issues of the work space - very nice flowers specially the top one - the bottom one has lost a lot of detail around the middle but this must be my monitor. Regards Robert

  13. #13

    Re: Histogram Colours ect

    Quote Originally Posted by Colin Southern View Post
    Hi Robert,

    A correct exposure will only get you so far.

    A reflective object only has a dynamic range of about 4 stops - most monitors will display around 6 - and most cameras will capture around 12 (but only show the top 5 or 6 on the in-camera histogram).

    This means that in essence "something has to give" ...

    If you get a middle gray to expose in the middle if the histogram then a reflected white will be 2 stops above that - but - the cameras will be able to record about 1 stop above that point - so it won't be a pure white as far as the camera and monitor are concerned.

    If you try to "get smart" and apply 1 stop of exposure compensation at time of capture so that the white is captured as a true highlight then - unfortunately - this also shifts the blacks up a stop as well, and what would have been a black - at 2 stops below middle gray - becomes only 1 stop (ie a reasonably dark gray, not a true black).

    So if you're displaying on a monitor then you MUST stretch the tonal range of the image from the 4 stops (maximum) that cover the reflective object into the (typically) 6 stops that a monitor displays so that both your highlight & shadow points correspond.

    If you don't then you'll have a tonal range offset, and that in turn will affect the perception of the colours.

    The second issue you'll have is with colour calibration. It's great that you're working from a profiled monitor, but the accuracy you're seeing is only as accurate as the profile that converts the camera's capture into the image that's presented to the monitor. In other words, if you're serious about colour management then you need to get that Color Passport ASAP. Think of it as a profile to correct for the camera/conversion inaccuracies much like the monitor profile corrects for monitor/display adaptor inaccuracies.

    The third issue is your lighting. Cameras have different response characteristics to the human eye - and using mixed lighting like you are is a bit like running your car on petrol ... with a little bit of diesel mixed in and a bit of oil mixed in for good luck too: In theory it'll handle it, but in practice, the performance won't be as good as if you stuck to just petrol.

    Hope this helps
    Hi Colin

    Thank you for your comments I find them very helpful

    Regards Robert

  14. #14
    Administrator Manfred M's Avatar
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    Re: Histogram Colours ect

    Quote Originally Posted by robertpobert View Post
    Hi Manfred

    Thank you for your comments

    I would like just to confirm that I do not look at the images out of my camera but look at the histogram and the raw files and this is what I meant by “out of camera” . I have been looking to acquire an X-rite passport and will do in the future but not until I am happy with the way I use my grey card(or a reference card) to set up my WB and my Exposure . I use a budget 24 inch screen which has been calibrated by a Spyder and will upgrade monitor one day soon. I need to have a good look at my lighting conditions and do more tests - I use white background and mixture of ambient (80%daylight and 20%florescent) and flash. The idea is to insulate every individual piece of the jigsaw and see the best way to control it – I am still fighting with histogram and trying to see how to draw the maximum out of it . Regards Robert
    Your budget screen may be part of your problem. I use a larger, higher end screen as my main screen and have a second, budget screen to for holding menus and other ancillary work. Even though I have calibrated both screens, the budget screen just does not want to display colours properly.

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