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[[Special:mylanguage/Showfoto/Brightness|Photo KDE Tutorial 1-4: Brightness/Contrast/Gamma + Hue/Saturation/Lightness]]
==Photo KDE Tutorial 1-4: Brightness/Contrast/Gamma + Hue/Saturation/Lightness==
Unai Garro - Summer 2008
I began this series of tutorials some time ago already, and all of them covered light issues. We used tools like [[Special:myLanguage/Showfoto/Levels_Adjust|levels]], [[Special:myLanguage/Showfoto/Curves_Adjust|curves]], or [[Special:myLanguage/Showfoto/White_Balance|white balance adjustment]].
I wanted to approach other type of issues this time, but I think light issues would be rather incomplete if I didn't address ''contrast'', ''brightness'' and ''colors'' adjustments. Possibly you are somewhat familiar with these already, but I think they're worth covering.
More than just a few times, we take a photograph of a gorgeous landscape, and we dream about the cool result we will get once we are at home. Nowadays digital cameras help us previewing the result on the LCD, but usually they are not too trustworthy, so we end up seeing the real results only when we are home.
So we arrive home with our cool photograph, and we find, disgusted, that it doesn't have the colors that we expected from it. What to do? We use '''Showfoto''' or '''Krita''' again, of course!
When I took this photo, my eyes were seeing all sort of strong green colors, and reddish leaves in the ground. But somehow the camera didn't capture all that contrast for me. But what's contrast? It's just the color differences found inside an image, the difference between a pixel/region and the surrounding. The more contrasty the image, the clearer it is to the eye.
This image instead, is whiteish, it's flat, it lacks contrast. Why? because it doesn't cover the whole histogram.
"Ahhhhhh..." you'll say now.... "I know this! I can fix this using <menuchoice>Levels</menuchoice>! I learned it in the first tutorial!". Yes, and that's what we will try first. Open the image in '''Showfoto''', and adjust the levels:
Not bad, is it? But still, I had a different photo in my mind. Leaves were greener, there was more contrast (like darker shadows), and the leaves on the floor were more reddish. So can we fix this? Yes, we could use the <menuchoice>Curves</menuchoice> to improve shadows for example. But I will show you some new tools that can achieve similar results in this case:
In '''Showfoto''', go to the menu <menuchoice>Color -> Brightness/Contrast/Gamma...</menuchoice>:
The first <menuchoice>Brightness</menuchoice> slider controls the brightness/darkness of the image. The second slider increases or reduces <menuchoice>Contrast</menuchoice>, and uhm... what's <menuchoice>Gamma</menuchoice>? Look at the following image:
The photo and histogram on the left are those of the original image. In the right hand, the three photos show the result of increasing brightness, contrast, and gamma respectively.
As you can see, when using the brightness control, it moves the whole histogram to the right. Shadows will disappear and become light grays. The result isn't very pleasing, as it is less contrasty. This could be fixed by adjusting contrast.
In the <menuchoice>Contrast</menuchoice> output, you can see that the histogram has been expanded. This means that each color has been separated further from each other, and thus increase color difference (contrast). The output is much more pleasing than the original image in this case. The image is no more flat, it's much more contrasty, and shadows are clear dark contrasted.
At this point you should have noticed something important. ''Both contrast and brightness controls can clip the histogram and cause information loss!'' Now look at the gamma adjustment. I pushed <menuchoice>Brightness</menuchoice> even further than the first tool, and still, the image wasn't clipped. What did the gamma tool do?
The <menuchoice>Gamma</menuchoice> control is like adjusting the curves tool upwards in the middle (see the figure). It affects mostly to the middle gray levels. Blacks will remain black and whites will remain white. (unlike <menuchoice>Brightness</menuchoice> control where blacks become gray). It compresses the histogram in the right part by compressing highlights, but shadows are expanded and thus causes to extend contrast there.
Given that this tool can clip the histogram, to avoid it as much as I can, I will change the order. Instead of doing <menuchoice>Levels</menuchoice> then <menuchoice>Brightness/Contrast/Gamma</menuchoice>, I will do <menuchoice>Brightness/Contrast/Gamma</menuchoice> then <menuchoice>Levels</menuchoice>. It's usually best adjusting levels after all other light adjustments have been done. So I did the following adjustment to the image:
I could have pushed contrast even further, but I prefer natural looking photos. Then, afterwards, even if it wasn't much needed due to the clipping, I adjusted levels a bit. This is what I got:
The result is similar to the previous one, but a bit more contrasty. Still, I'm missing colors here, something is missing? Of course, lets open the <menuchoice>Color -> Hue/Saturation/Lightness...</menuchoice> option from the menu:
It will open a dialog where '''Showfoto''' permits adjusting the colors of the image. The <menuchoice>Saturation</menuchoice> control can make colors stronger or weaker. The <menuchoice>Hue</menuchoice> control permits altering colors towards another one (brighter colors to darker green, or even to yellow...), and finally, <menuchoice>Lightness</menuchoice> can make colors brighter or darker. When the image is lightened up, it causes moving the histogram's dark part upwards and compressing the whole of it on the right, thus blacks dissappear and contrast can be reduced easily thanks to the compression.
In my adjustment, I pushed saturation up to 34, reduced lightness a bit, and retouched the greens by altering the hue slightly. This is what I got finally:
Thanks for reading this tutorial and I hope you found it useful. Cya on the next tutorial!
------
Notes:
{{Note|1=1. Please note that it's very easy to get addicted to tools like saturation control and go too far adjusting them (we call it overdoing /overprocessing). We want more colors, more saturated colors... but we end up with a picture that looks very unnatural and clearly shows processing was done. My suggestion is you limit yourself to showing what your eyes or your mind saw in the scene without overdoing the photo.}}
{{Note|1=2. The final image was also sharpened a bit for presenting. We will cover sharpening in the following tutorials.}}
{{Note|The original image used in this tutorial [http://userbase.kde.org/File:Curves_adjust.jpg can be found here]. }}
This is the second part of tutorials aimed at showing how to use KDE's photography tools (namely '''ShowFoto''' and/or '''Krita'''), to process, edit and fix your photographs. The [[Special:myLanguage/Showfoto/Levels Adjust|first part of the tutorials]] showed how to interpret a ''histogram'', and how to use the ''levels'' tool. This tutorial will show you how to use a more advanced tool, called the ''Curves Adjust'' tool. It's much more powerful than the levels tool but requires more patience and practise to get good results.
So lets begin. This time we have this photo, kindly donated for the tutorial by Jos van den Oever, from his akademy 2008 photos.
The problem in this photo again, is that there are parts of the image that are very dark. The two people are clear in the photo, but the background is so dark that we cannot actually see the pub's details. Let's see what happens if we try using the ''levels'' tool, as we learnt in the first tutorial:
As you can see, some parts of the image get blown if we try using the levels tool. What does that mean? It means that we have parts of the image in the right hand of the histogram that have been all converted to white. That's because, unlike the previous tutorial, this image is not concentrated on the left part of the histogram. It covers the whole of it. And when clipping the histogram with the input sliders, we are "eating" part of the information.
Why does this happen? Because the photo scenario had a very ''High Dynamic Range''. i.e. it had objects from very dark (background) to very bright (illuminated by flash).
In this sort of images, if we try moving the input sliders of the levels tool, we will delete part of the photo's gray level information, losing details, and the result isn't nice.
So what to do now? We can use the <menuchoice>Curves Tool</menuchoice> from the menu <menuchoice>Colors -> Curves Adjust...</menuchoice>: [[Image:Adjustcurves.png|20px]]
Selecting this option will show a new popup with a dialog that may look similar to the levels tool. You can see the resulting histogram on top, and the input histogram on the bottom, just like in the levels tool:
The difference is in the way the control works. In this tool, the input histogram has a diagonal line in it. Clicking on it with the left button of the mouse, adds control points. You can move those control points up or down. The result, as shown in the picture above, is that the gray levels from the horizontal axis are converted into the gray levels in the vertical axis.
Moving the control points up, makes that part of the image brighter. Moving them down, makes that part of the image darker.
In this case, I wanted to make the darkest parts of the image brighter, so I added a control point on the left part of the histogram, and moved the point upwards. As the rest of the image was also getting a bit too bright, I added a second control point to avoid it.
We have managed to make the shadows brighter, and now the pub is more visible, but the image is now a bit washed out. As if it were too bright all over the place. Can we do something? Sure, lets try the levels adjustment again:
Now that the shadows were adjusted using the curves, and the colors are more uniform, we can follow the method shown in the first tutorial and adjust the levels of the photo, as shown above. The histogram's main data was a bit displaced to the left, and adjusting levels, I made it cover the whole range again.
Lets see the result - Ah, now this is much better. The pub background is much more visible and the two persons are not blown:
I think that's already acceptable, but if we are picky, the two people are a bit washed out due to the flash light. So, even if that goes out of the scope of this tutorial (it'll be covered in the following tutorials), lets adjust a bit the ''saturation'' and ''contrast'' in the image for a better result:
Now this image looks much nicer than the original, yes. I hope you liked this tutorial and will see you in the next one!
{{Note|The original image used in this tutorial [http://userbase.kde.org/File:Levels_adjust.JPG can be found here].}}
This is possibly one of the most widely used and most simple method to adjust an image. It's so simple and effective that you will want to use it on all your pictures from now on, so keep an eye on this, and have fun.
You'll clearly see, the photo is darkish. After all, it was taken during a presentation and possibly the room was pretty dark. But that's no excuse for a bad photo [[Image:Face-smile.png|12px]]
Why is it dark? Lets open the photo in '''Showfoto''' ('''Digikam''''s editor) and see what's going on:
On the top right, you can see the image's ''histogram''. (I have pushed the <menuchoice>Linear</menuchoice> histogram button to see it more clearly).
So "What's the histogram?", you'll, ask. The histogram is just a pixel count. It counts how many pixels there are for each gray level, and shows them in a graph. The left part of the histogram are dark/black colors, and the right part of the histogram are brightest colors.
You can see that our image has the histogram concentrated on the left part. Thus, it's mostly black. The right part of the histogram isn't used at all, as shown in the figure. Why did this happen? Just because the camera failed exposing the image properly, or was inappropriately configured.
If a photo is visually pleasing, usually (not always), it covers most of the histogram, from black, to white.
So, is there a way to fix this, then? Of course there is, and it's a very easy one. Select the menu <menuchoice>Color -> Levels Adjust</menuchoice>:
You will see a new popup showing a tool to adjust the histogram output. There are several parts in it. On the top right, there are two histograms. The first one is the ''output/new'' histogram, and the second (bottom) one is the ''input/original'' histogram.
As you can see, I have adjusted the output histogram to cover it all, see? So how have I done this? Very simple:
There are 4 sliders in this tool. The first two sliders (top bar, "Input Levels") mark the upper and lower values of the histogram that I am interested in. I have moved them to match the full histogram of our original image.
The other two sliders (bottom bar, "Output") mark the range of the histogram we want as output. We want the histogram to cover from black to white, so just move the sliders to the left corner and to the right corner.
Beneath each bar are controls that can be used to manually enter values for the upper and lower values. The keyboard or up and down arrows can be used. This allows for finer-grained control over using the sliders.
Press <menuchoice>OK</menuchoice>, et voilà, your nice photo is fixed. Congrats [[Image:Face-smile.png|12px]]
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