Translations by Aliyar Güneş

The human visual system is not a simple RGB sensor, but we can approximate how the eye responds with a CIE 1931 chromaticity diagram that shows the human visual response as a horse-shoe shape. You can see that in human vision there are many more shades of green detected than blue or red. With a trichromatic color space like RGB we represent the colors on the computer using three values, which restricts up to encoding a <em>triangle</em> of colors.

Using models such as a CIE 1931 chromaticity diagram is a huge simplification of the human visual system, and real gamuts are expressed as 3D hulls, rather than 2D projections. A 2D projection of a 3D shape can sometimes be misleading, so if you want to see the 3D hull, install <code>gnome-color-manager</code> and then run <code>gcm-viewer</code>.

sRGB, AdobeRGB and ProPhotoRGB represented by white triangles

First, looking at sRGB, which is the smallest space and can encode the least number of colors. It is an approximation of a 10 year old CRT display, and so most modern monitors can easily display more colors than this. sRGB is a <em>least-common-denominator</em> standard and is used in a large number of applications (including the Internet).

AdobeRGB is frequently used as an <em>editing space</em>. It can encode more colors than sRGB, which means you can change colors in a photograph without worrying too much that the most vivid colors are being clipped or the blacks crushed.

Bigger steps mean a larger error between the captured color and the stored color, and for some colors this is a big problem. It turns out that key colors, like skin colors are very important, and even small errors will make untrained viewers notice that something in a photograph looks wrong.

Color management is a process for converting from one color space to another, where a color space can be a well known defined space like sRGB, or a custom space such as your monitor or printer profile.

Calibrating is important if you care about the colors you display or print.

Why do I need to do calibration myself?

Generic profiles are usually bad. When a manufacturer creates a new model, they just take a few items from the production line and average them together:

Averaged profiles

Display panels differ quite a lot from unit to unit and change substantially as the display ages. It is also more difficult for printers, as just changing the type or weight of paper can invalidate the characterization state and make the profile inaccurate.

The best way of ensuring the profile you have is accurate is by doing the calibration yourself, or by letting an external company supply you with a profile based on your exact characterization state.

Color management is important for designers, photographers and artists.

Why is color management important?

Color management is the process of capturing a color using an input device, displaying it on a screen, and printing it all whilst managing the exact colors and the range of colors on each medium.

The need for color management is probably explained best with a photograph of a bird on a frosty day in winter.

A bird on a frosty wall as seen on the camera view-finder

Displays typically over-saturate the blue channel, making the images look cold.

This is what the user sees on a typical business laptop screen

Notice how the white is not 'paper white' and the black of the eye is now a muddy brown.

This is what the user sees when printing on a typical inkjet printer

The basic problem we have here is that each device is capable of handling a different range of colors. So while you might be able to take a photo of electric blue, most printers are not going to be able to reproduce it.

Most image devices capture in RGB (Red, Green, Blue) and have to convert to CMYK (Cyan, Magenta, Yellow, and Black) to print. Another problem is that you can't have <em>white</em> ink, and so the whiteness can only be as good as the paper color.

Another problem is units. Without specifying the scale on which a color is measured, we don't know if 100% red is near infrared or just the deepest red ink in the printer. What is 50% red on one display is probably something like 62% on another display. It's like telling a person that you've just driven 7 units of distance, without the unit you don't know if that's 7 kilometers or 7 meters.

In color, we refer to the units as gamut. Gamut is essentially the range of colors that can be reproduced. A device like a DSLR camera might have a very large gamut, being able to capture all the colors in a sunset, but a projector has a very small gamut and all the colors are going to look "washed out".

In some cases we can <em>correct</em> the device output by altering the data we send to it, but in other cases where that's not possible (you can't print electric blue) we need to show the user what the result is going to look like.

For photographs it makes sense to use the full tonal range of a color device, to be able to make smooth changes in color. For other graphics, you might want to match the color exactly, which is important if you're trying to print a custom mug with the Red Hat logo that <em>has</em> to be the exact Red Hat Red.

Disks &amp; storage

When the test is finished, the results will appear on the graph. The green points and connecting lines indicate the samples taken; these correspond to the right axis, showing access time, plotted against the bottom axis, representing percentage time elapsed during the benchmark. The blue line represents read rates, while the red line represents write rates; these are shown as access data rates on the left axis, plotted against percentage of the disk traveled, from the outside to the spindle, along the bottom axis.

If the status says "Pre-fail", the disk is still reasonably healthy but signs of wear have been detected which mean it might fail in the near future. If your hard disk (or computer) is a few years old, you are likely to see this message on at least some of the health checks. You should <link xref="backup-how">backup your important files regularly</link> and check the disk status periodically to see if it gets worse.

Sticky Edges

Under <gui>Select a disc to write to</gui>, choose the blank disc.

(You could choose <gui>Image file</gui> instead. This will put the files in a <em>disc image</em>, which will be saved on your computer. You can then burn that disc image onto a blank disc at a later date.)

You can select files in a folder using a pattern on the file name. Press <keyseq><key>Ctrl</key><key>S</key></keyseq> to bring up the <gui>Select Items Matching</gui> window. Type in a pattern using common parts of the file names plus wild card characters. There are two wild card characters available:

<file>*</file> matches any number of any characters, even no characters at all.

To transfer the file to a Bluetooth device, select <gui>Bluetooth (OBEX Push)</gui> and select the device to send the file to. You will only see devices you have already paired with. See <link xref="bluetooth"/> for more information.

You can sort files in different ways in a folder, for example by sorting them in order of date or file size. See <link xref="#ways"/> below for a list of common ways to sort files.

The <gui>Compact Layout</gui> option in the <gui>Arrange Items</gui> menu arranges the files so they take up as little space as possible. This is useful if you want to have lots of files visible at once in a folder.

Quickly create new documents from custom file templates.

Many computers contain readers for SD (Secure Digital), MMC (MultiMediaCard), SmartMedia, Memory Stick, CompactFlash, and other storage media cards. These should be automatically detected and <link xref="disk-partitions">mounted</link>. Here are some troubleshooting steps if they are not:

Move keyboard focus between different controls. <keyseq><key>Ctrl</key> <key>Tab</key></keyseq> moves between groups of controls, such as from a sidebar to the main content. <keyseq><key>Ctrl</key><key>Tab</key></keyseq> can also break out of a control that uses <key>Tab</key> itself, such as a text area.

Move selection between items in a single control, or among a set of related controls. Use the arrow keys to focus buttons in a toolbar, select items in a list or icon view, or select a radio button from a group.

You can set it so that the two displays have different resolutions, but you won't be able to display the same thing on both screens simultaneously. In effect, you will have two independent screens connected at the same time. You can move windows from one screen to another, but you can't show the same window on both screens at once.

Double-clicking only happens when you press the mouse button twice quickly enough. If the second press is too long after the first, you'll just get two separate clicks, not a double click. If you have difficulty pressing the mouse button quickly, you should increase the timeout.

Under <gui>Double-Click Timeout</gui>, adjust the <gui>Timeout</gui> slider to a value you find comfortable. Use the smiley face under the slider to test your settings. A single click will make it smile. A double-click will give it an ear-to-ear grin.

If your mouse double-clicks when you want it to single-click even though you have increased the double-click timeout, your mouse may be faulty. Try plugging a different mouse into your computer and see if that works properly. Alternatively, plug your mouse into a different computer and see if it still has the same problem.

Change how far you have to move your mouse pointer to start dragging.

Adjust the mouse drag threshold

When you click something, it's not uncommon for your hand to move a little between the time you press the mouse button and the time you release it. For this reason, dragging only starts if you move the pointer past a certain threshold, so that you don't accidentally start dragging every time you click. You can control the minimum distance required to start dragging.