3. Adjusting color and brightness
The picture looks better now, but it's still too dark. We can do brightness and color adjustments with the various tools hidden under the Tools->Color Tools menu:
There's a simple brightness/contrast control in there that is pretty self-explanatory, and also tools for adjusting the color balance in various ways. But my preferred ways of making these adjustments are with the Levels and Curves tools, which give you more control. Here's Levels:
This is the most complicated tool I'll be covering here, and it has a lot of controls. Several of them are actually pretty handy, so I'll mention most of them. They affect the color and brightness of the image in various ways.
If the box marked Preview is checked, then while you work in the dialog, the appearance of the view window changes to preview what the tool is going to do. (If nothing seems to be happening to the picture when you make adjustments, make sure the Preview box is checked.) The changes aren't permanent until you click on the OK button, though, and you can reset them to where you began by clicking on the Reset button at the bottom.
The button marked Auto will attempt to automatically adjust the image. Sometimes, that's all you need to make the picture look good. Sometimes it's not. It's usually worth a shot. If you don't like what Auto did, you can always Reset it away.
The three eyedroppers next to the Auto button can be extremely useful, especially if you are trying to fix a picture that has a weird-looking color cast to it (because, say, you had the white balance on your camera set wrong, or the light was funny). They pick the black point, gray point, and white point respectively. If you click Pick Black Point and then click somewhere in the picture that you think is supposed to be absolutely black, the tool will adjust the whole image's brightness so that it becomes black. Pick White Point does the same thing with white: it adjusts the brightness and color so that the selected point is a pure, maximum-brightness white.
Pick Gray Point is a little different: it only adjusts the color (that is, hue and saturation), not the brightness. If you click somewhere that you think is supposed to be a neutral gray (such as a white wall), the tool will adjust the colors of the whole picture so that any color cast is removed and that part of the picture looks gray. Of course, if you didn't happen to photograph any gray or white objects, this is not so useful. Clicking on something that is not supposed to be gray can produce strange and freaky effects that you might find amusing.
Right now, though, I'll just play with the controls near the top of the dialog. The black and white graph is called the histogram; it shows the distribution of pixels of different brightnesses within the image. Black is at the left end, and white is at the right end. Right now the histogram is showing overall brightness (also known as "value"). As you can see, the pixels in the original image don't go all the way up to maximum brightness. There are three peaks in the distribution. The lump nearest the dark end is probably the range of brightnesses of Niobe herself (and the bookshelf); there's a narrow spike corresponding to the shade of gray in the back wall, and the other lump is the brightness of the bright bedspread.
You can click and drag the three little triangles just below the histogram to adjust the brightness levels in the image. The tool will adjust the colors so that the positions of the black, gray, and white triangles will map to the minimum, middle, and maximum brightness values respectively.
If you move the black and white triangles so that they are at the very edges of the black curve in the histogram, the image will be adjusted such that the very darkest pixels in it become black and the very brightest pixels become white. This will usually give you the best-looking constrast (but there are always exceptions; don't be afraid to experiment). Then you can move the gray triangle around to further correct the brightnesses in between.
(The above description may have been opaque. I recommend using the tool on an image and moving these three triangles around for a while to see what they do. Remember, nothing you do in this tool is official until you click OK, and even then you can always use Control-Z to undo.)
With the menu above the histogram, you can make it so that it just shows (and controls) brightness in the red, green or blue color channel. This can be useful for color adjustments, but I think the color of this picture is already all right.
In many cases, the Levels control is enough to give your image the brightness and color that you want. If you need finer control, you can use the Curves tool. I am picky and I end up using this most of the time.
This tool has a histogram in it that looks much like the one in the Levels tool. Superimposed on it is a curve, which starts out as a straight line. The curve represents the before-to-after mapping of initial brightness to the final brightness that the tool will produce. Initial brightness is on the horizontal axis, and final brightness is on the vertical axis. You can adjust this curve by clicking and dragging. Clicking will make a new control point that you can then drag around to move the curve. (If you need to get rid of a control point, drag it off the left or right edge of the dialog.) Again, if the Preview box is checked, the image will change to preview what you're doing, but it's not permanent until you click OK.
In the figure, I've made a curve that maps the brightest pixels in the image to white, the darkest ones to black, and bows up a little in between to brighten things up generally. You can exert subtle control over the image by changing the shape of the curve. Usually two or three control points will suffice, but you can use more for purposes of extreme image repair. In general, wherever the curve has a steep slope, the parts of the picture with that range of brightnesses will have a lot of contrast. Wherever it is shallow, the picture will tend to look flat and washed-out. By adjusting the shape of the curve, you can give the most contrast to the things that you think need it.
As with Levels, you can use the pop-up at the top to control the red, blue and green levels of a color picture separately. This is useful for adjusting the color balance when the eyedroppers in the Levels dialog aren't enough. Here, I'm satisfied with the color so I'm just working on value.
I like the results here better than what I did with the Levels tool, so I'm keeping them in what follows.
In the option pane for the Levels and Curves tools, there's a "Histogram Scale" option with "Linear" and "Logarithmic" settings. The little icons in the upper right of the Levels and Curves dialogs represent the same thing.
These just have to do with the display of histograms in the dialogs. In "Linear" mode, the histogram height maps directly to the number of pixels of a given brightness in the image. In some cases, though, you might have an image where most of the pixels are the same color, and that makes a peak in the histogram that is so tall that the other values all get crunched down to nothing just to fit the tall peak into the graph. The histogram can become almost useless because you can't see anything in it. In order to see the rest of the histogram better, you can pick "Logarithmic", which exaggerates the little values relative to the big ones.
Next: Sharpening