The Levels Tool in XPE (Xara Xtreme Pro only)

Owners of Xara Xtreme Pro have a Levels tool that is part of Xara Picture Editor. This tool allows more advanced control over brightness levels than the normal brightness / contrast. In fact the Levels tool is a very powerful feature that can adjust color casts, as well as providing a histogram of the overall brightness levels.

Here is an example photo that's rather too dark. Many digital cameras get the exposure of images like this wrong where there's a bright sky behind an object. Here it has set the exposure to get the sky detail rather than the foreground detail.



To open the Level tools, just double click on the photo in Xara Xtreme Pro (you can just drag the photo in from your file explorer to open it in Xtreme).



Along the bottom are the usual set of tools, but Xara Xtreme Pro also has the Levels tool, indicated. Click this and it displays a histogram of the brightness levels in this picture, like this:



This is a graph of the brightness levels, going from dark color on the left side to light color on the right. The more red area, the more of that range of shades in the picture. So in this case there are two peaks. You can tell from the photo that the dark peak is a result of all the dark buildings in the image. The other peak is a result of the sky (this photo contains little else which is why there are just two clear peaks like this).

Every photo is different and produces a different histogram. This is from a more typical, better exposed photo. A typical ideal is to have a range of all shades in a photo.



The Levels histogram is such a powerful tool because it enables you to tell at a glance the overall mix of brightness levels of any photo. You soon get to recognize over-exposed or under-exposed pictures. By using the controls it is quite easy to adjust the brightness levels and see the affect that this has on the histogram.

The Levels control has 5 separate values you can change, either by entering values in the fields or by dragging the appropriate slider control in the dialog. The three main slider controls are shown above, which control the adjustment of three parts of the histogram: the dark, mid and light shades. What the Levels control is doing is really mapping input shades to output shades. This sounds a bit complicated but really is not. So, for example, by adjusting the dark shades slider control to the right you are simply saying that you want the dark shades to become lighter. In other words, the input (before) darker shades become paler on the output (after). Dragging the white slider to the left you are making the paler shades become more dark. So again, the lighter shades of the input (the before case) are being mapped to darker shades on the output (the after case).

Overlaid the red histogram is another graph (the green line), which represents the actual mapping curve, going from dark in the bottom left corner to light in the top right. For the technically minded the vertical axis of the green levels curve is different to that of the histogram. The histogram vertical axis represents the amount of any given shades in the picture. The higher the red, the more of that shade there is. For the green curve, the vertical axis (like the horizontal axis) represents dark to light shades of the output levels. A straight green line (the start position) means there's no re-mapping or adjustment. Dark shades along the bottom are mapped to dark shades up the side. And at the other end, white shades at the right side are mapped to white output shades.

When you adjust the slider control both the green curve is altered, reflecting how the shades in the photo are remapped, and the histogram changes showing the actual new mix of brightness shades in your photo.

The gray slider

The middle slider adjusts the gamma - that is mid to dark shades are affected more than the light shades. This is a very useful control since one of the most common problems with photos is that they are under-exposed - with large dark areas. Below you can see I've dragged the gray slider to the right. This alters two parts of the histogram, as you can see below. The green mapping line is now a curve, and you can see that it bulges at the dark end. That is that darker input shades along the left bottom are now mapped to higher shades up the side. In other words, darker shades are made lighter.



And the red histogram has changed correspondingly. The left peak has now moved rightwards, in other words, to be lighter colors. Note also that the right peak has changed nowhere near as much. Finally, you can see from the picture that the detail of the foreground building is now completely visible and much brighter. The black histogram is the 'before' state so it's easy to compare the new red histogram with the before state.

It's worth noting that had you used a normal brightness control on this image all shades would have become equally brighter. This would have resulted in the sky burning out and probably becoming almost white. It's clear that this type of gamma brightness change is much better for this picture.

But there is one new problem. As I mentioned earlier, the ideal picture has a good spread of shades, but if you look closely at the above histogram the first red peak is now quite a way from the dark end.



This means that the picture no longer contains really dark shades, and indeed, the photo could be said to be slightly washed out. To fix this you can adjust the black slider to the right, just enough to bring the left side of the histogram to the left side of the graph to create a more even spread of darker shades, that goes all the way to black.



As you might see, the black slider has been dragged slightly rightwards. The fields at the top show the actual values used. You can see the black setting is 10, the gamma setting is 1.80, the white setting remains unchanged at 255. The resultant picture now has a better spread of dark shades. Compare it with the original to see how much better this is.



You can find out more about the Levels Tool in this month's second tutorial.