Whether you are working with a colour or black-and-white image, you would be ill-advised not to spend some time checking your colour or tonal levels.
Every time I open a photograph within Adobe Photoshop, one of the first things I do is ensure that the image is not discoloured or impaired as far as colour and contrast are concerned. Invariably, images caught with either a digital camera or acquired using a flatbed scanner will lack the deep and rich range of tones that you’d expect to see in a high-quality photograph.
Within Adobe Photoshop are a several methods you can use to improve your image and push it toward a professional standard. The method covered up within this tutorial centres around the use of the function called levels.
Levels allow you to control the contrast, luminosity, hue and using an apparatus called a histogram.
let’s start by opening up an image. Firstly, to keep things simple, we going to experiment using a black-and-white photograph. Locate an image which has poor contrast, is faded or is too dark. Within this tutorial I will use this image.
Now that we have our photograph loaded into adobe Photoshop, we will now need to access the levels dialogue box. It can be loaded by visiting the image menu at the top of the screen, and then by clicking on adjustments – and choosing levels from the submenu. The quick key for this function is CTRL-L.
If you have never seen the levels dialogue box before, you may feel a little daunted. Although a histogram may look complex, the concept behind it is rather simple. A histogram can be described as a highly detailed bar chart displaying the frequency of distribution of information across a plain. In this particular case, the distribution of tonal information across the tonal range between black and white. This range is set from 0 which represents black, to 255 which represents white. All together including absolutely black, there are 256 individual shades.
By looking at a histogram, eventually you will be able to determine the condition of your image. Whether or not it is too dark or too light or lacks contrast or contrast levels are too great, all of these prognoses can be established from observing a histograms shape.
I can tell from looking at my histogram, that this image lacks heavily in contrast. I know this because most of the tones within my histogram are huddled up within the centre of the tonal range. There is no or very little information at either the darker and lighter ends. This effectively means that there is a definite lack of very dark and very pale detail within my image.
Now, let’s take a look at how to correctly optimise our image using levels so to improve the contrast. Effectively, all we need to do is stretch the tonal information from the black to the White end of the tonal range. We can do this by the re-establishing the black point and the white within our histogram. This can be done by clicking and dragging or sliding the small triangles, the black and white points either side of the tonal range, up to the points where the frequency of tonal information really starts to lift.
You can start from either end. I think in this case I will work from left to right. I simply need to bring the black point up to where the frequency of tones within the histogram begins or, at least, starts to take on a greater presence. And then I’ll turn my attention to the lighter end, again bringing in the white point in.
If you haven’t already noticed, the image behind the levels dialogue box has now significantly improved. These changes will not become permanent until I click on OK. All you are seeing at this stage is a very accurate preview.
While we are on the subject of accuracy, of course, it is important to ensure that we don’t end up inflicting more harm than good on our photograph by applying levels. If we were to drag our black and white points in too far, we run the risk of losing detail from our image. You are effectively cutting off information from the tonal range by doing so. If you want to be absolutely sure that you are manipulating your histogram correctly, hold down the alt key on your keyboard or options key if you are using a Mac whilst clicking and dragging the black and white points.
You can now see directly how the frequencies within the tonal range relates to your image behind the levels dialogue box. For accurate positioning, whilst holding down the alt or options key, drag the black and white points in in turn until you start to see small pixels of information appear. The aim is to tolerate these pixels up until the point that they start to form clumps. If you can see clumps of pixels forming, then you are going too far over. Back off a little. There.
Once you have correctly re-established the black and white points, you can then turn your attention to tweaking your image so that it now appears as you want it too. Although the contrast looks great, your image may still be a little lighter or darker than you’d prefer. In this case, all you need to do is change the mid point. The mid-point in the central slider in-between your black and white points. This point control, the weighting of tonal information toward either the black or white ends of the tonal range. Experiment with sliding the mid-point to the left to lighten and the right to darken.
Once you have done this, you are now ready to commit to these changes by clicking on OK.
This method works well for the vast majority of images but not in all cases. Some photographs still require tweaking by eye. In those cases I’d suggest you firstly follow the methods outlined within this tutorial and then play around with the settings, pushing out the black and white points and/or changing the position of the mid-point.
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