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    Adjusting white balance and contrast

    Adjusting the white balance and contrast Par Digital Focus (@Lesnums), Samuel Boivin Posted on 06/02/18 at 14h00 Share:

    La white balance is a setting often overlooked by too many beginner photographers, even though it plays a key role in color rendering and, therefore, the realism of the photo. We will see in this article when and how to adjust it, as well as the contrast which goes hand in hand with this parameter.

    White Balance Reminder

    Because today the automatic white balance mode is effective in more than 90% of situations, many neophyte and amateur photographers are unaware of its operation, whereas it is important to master it well to sometimes get out of situations. luminously complex.

    The white balance is used to faithfully transcribe the colors of the ambient light, because if the human eye knows how to adapt so that our vision of colors is more or less constant depending on the light source, this is not the case with the photographic sensor.

    Indeed, depending on the source, the light spectrum is not always the same and our perception of colors may therefore differ. We then speak of color temperature expressed in kelvin (K). Each light source having its own more or less warm temperature, the tint will differ from one source to another, and it is the role of the white balance to indicate to the photographic sensor that it is the temperature in order to transcribe the colors as we see them.

    We quickly realize here that the photo has a too yellow tint compared to reality.

    For example, a tungsten bulb has an average temperature of 3 K, which is quite warm and therefore orange in hue, whereas the sun at its zenith has a temperature around 5-200 K, i.e. a cooler, bluer light. If the white balance is not set at the correct temperature, all colors may have a tint that is too blue or too orange.

    In addition to this warm or cold dominance, there is also a green or magenta tint that is complicated to correct with the naked eye. This tint, which can quickly make a photo look ugly, is often due to artificial lighting. Because if the Sun projects a light composed of a continuous spectrum, it is not the case neon lights and compact fluorescent bulbs for which the space of a microsecond, part of the spectrum is missing, and therefore a color that composes it, which can thus give a green or magenta hue depending on the moment.

    Example of composition of a light spectrum according to the source and its color temperature.

    Fortunately, all these constraints can be easily lifted, provided you know how to adjust the white balance, whether during shooting or in post-production.

    Adjusting the white balance from the camera

    From your camera, whatever it is – even smartphones – you can directly choose your white balance according to three measurement modes…

    → La balance auto or AWB.
    → Predefined modes.
    → The personalized scale.

    Auto or AWB mode

    In the Settings menu or via the WB button on your camera, you just have to choose the Automatic or AWB (Automatic White Balance) mode. Your camera will then automatically measure the amount of each color to make the white in your photo as white as the scene you are shooting, as much as possible. In most cases, the balance is correct and this metering mode is perfect if you shoot in RAW, because you can fine-tune it later in your development software. On the other hand, if you shoot in JPEG and the white balance is incorrect, it will be more difficult to catch up perfectly, the JPEG not leaving as much freedom as the RAW.

    If you know the primary light source in your scene and are shooting in JPEG, don't trust your camera's auto metering mode, or have the wrong balance, the preset mode can be a great help. Be careful all the same to anticipate that if the light source changes radically, the rendering of the photo may be surprising. Especially in JPEG where a large temperature difference will surely not be recoverable.

    Concretely, on the example below, by photographing this scene under a light bulb, the auto balance provides a correct balance, but not in all respects perfect: the Sun preset is totally wrong and gives a color that is much too orange whereas the preset Bulb is the one that comes closest to seeing the human eye with a truly white tint.

    Custom white balance

    This type of adjustment is mainly intended for those who photograph directly in JPEG since it is of almost no interest in RAW.

    In practice, you will manually set the exact temperature of the light source via predefined steps, you won't have to advance step by step. To do this, you will need a reference object, a white sheet for example, and if possible the liveview of your camera. While it's possible to do this by trial and error, it's much more convenient than going into your menu, selecting a value, taking a picture, viewing it, and repeating until you get a correct value.

    If a sheet of white paper does the job very well for a good rendering, it is still preferable to use a calibration chart for perfect rendering.

    Adjust white balance in post-production

    To adjust the white balance to perfection, the best way (at the risk of repeating ourselves) is still to shoot in RAW and in Auto or AWB balance mode. Then, using your development software (Lightroom, Camera RAW, Capture One, etc.), all you have to do is adjust the temperature and tint to achieve the perfect balance. However, there are at least two techniques to achieve this, either with the naked eye or via the photo witness technique.

    To the naked eye

    This is the most commonly used technique. In Lightroom or any other development software, compared to the lighting atmosphere that you photographed, the scene seems too orange to you, for example. You'll then change the color temperature until you get something that comes closest to the actual mood.

    To help you, and if you have a neutral zone in your photo (white wall, etc.), you will click on this zone using the pipette and the temperature will change automatically in order to make the white perfectly white.

    If the result is technically good since the white is perfectly white, it will not necessarily be perfect since your reference zone was not necessarily perfectly white when the shot was taken. Do not hesitate to warm up or cool down the temperature to obtain a satisfactory result.

    By wanting to improve the basic photo via a pipette on the white strip of the jogging of the man in the foreground, the balance is in the end more incorrect than at the start.

    Needless to say that to work with the naked eye on the white balance, it is preferable to work on a calibrated screen, because if the latter is not calibrated and displays a dominant hue, it will be complicated to work precisely.

    The photo witness technique

    You will have understood that if the pipette can be of great service with the previous technique, the latter is far from being infallible since we know almost nothing about the reference zone, which can sometimes give very far from the desired effect. For personal photography, perfection is not always necessary: ​​imagine having to shoot for a client whose color rendering must be faithful, because this same color is an important part of his visual identity, or simply to respect the different skin tones during a portrait session. It is therefore advisable to use the photo test technique using a calibrated test chart.

    Generally composed of a color chart as well as patches of white, gray – including an 18% gray – and black, we can be sure that the colors of the chart are perfectly neutral and that the surface reflects all the light rays in equal parts. of all the colors.

    In practice, once your scene and your lighting have been set up and before taking your first photo, you will place the target in the field or have it held by your subject. Take a first witness photo then, as long as you don't change your lighting or light source, you remove it from the field and work as you are used to.

    Once in your development software, import all your photos, including the witness photo. On the latter, using the white balance eyedropper, click on the white patch to obtain a true-to-life balance. You will only have to transfer the result to the rest of your shoot and work as you are used to while being certain that your scale is technically faithful to reality.

    Contrast adjustment

    In ordinary times, the sensor manages the contrast of the image quite well when shooting depending on the light conditions, but it is also possible to correct it by post-production.

    As a reminder, contrast is the difference in brightness between the light and dark parts of your image. Concretely, on your device or in your development software, it is represented by the spread of the data over the entire histogram. A high-contrast photo is often considered to have a filled histogram from left to right without touching the edges, that is, with unobstructed dark tones and unburnt light tones. If the histogram touches the edges too much, then the photo has too much contrast, causing loss of detail in those areas. Conversely, a photo whose histogram data is too centered will lack contrast and appear dull. That said, it's also a matter of taste or atmosphere...

    To correct the contrast, you can view the histogram on your screen when shooting and, if necessary, repeat it by modifying the contrast value directly in your camera's menu.

    But can also correct it in post-production. Again, if you shoot in RAW rather than JPEG, the correction will be easier, as it is non-destructive. To do this, there is no miracle solution, you will have to feel your way, keeping an eye on your histogram to check that you are not going too hard and on the rendering of your photo to check that you still keep the atmosphere you wanted to create. Again, what is technically perfect is not necessarily visually perfect.

    We clearly see here the impact of the contrast on the image and the histogram.

    However, at the risk of rambling, be aware that by using a target when shooting, you will be able to help your camera to better interpret the exposure necessary in order to obtain a sufficiently high-contrast rendering. Indeed, the contrast being the difference in luminosity between the darkest and lightest parts – therefore also of the exposure –, the light meter of the case will be able to rely so much on the light reflection made on the gray at 18%, as well as only white and black patches to offer you the best exposure possible, and therefore the contrast. However, you will certainly still need to edit it in post-production. When the sun is at its zenith or the landscape is completely foggy, it is difficult to have a technically perfect contrast.

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