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darktable Chapter 6 part 2: 'color group' plugins
And speaking of color, lets pass to the next plugin,
which is one of the classics in programs like Photoshop or Gimp,
and its operation is the similar.
Image files have their information divided into channels (eg RGB),
and using this tool we can alter the details
of each of the channels.
We can choose, beside RGB,
gray channel and channels LSH (Luminance, Saturation, Hue).
Its handling is very simple.
For example, if we choose the red channel,
we see that the information is divided this way:
Red has 1 (100%), green and blue are 0.
This is the normal situation for this channel.
If we alter the red slider in the red channel,
the picture changes hue and the same happens
if we play with the rest of the sliders.
Always be careful with the changes made in RGB
because they alter the lightness of the picture,
unlike in other modes, such as LAB.
You see that the changes are enormous,
if we look at the before and after... it's not bad, right?
One of the interesting things that can be done
when we work the color of an image,
which can be unintuitive, is the Black and White.
'Channel Mixer' is one of the basic tools to work on developing this style.
For this we choose the gray channel in 'destination',
and nothing happens,
but it should automatically become black and white.
If this happens to you what you have to do is choose the preset "b/w"
and then we can work with the sliders to adjust the result.
Although the picture is a scale of grays,
color information is still there,
the colors are now represented as degrees of brightness,
and their values can be altered using the mixer.
Once you have passed it to black and white
you can continue working with the rest of the color group plugins.
In darktable website we can find a PDF manual,
in which we have a list of channel mixer settings
to mimic classic Black and White films.
To save this data you can change the values of the different sliders,
entering the data given in the manual
and save the settings as a preset.
This way we have a good collection of black and white film presets.
Output color profile':
this is a tool with a technical purpose.
Color management is a fundamental process for good results
in the development of RAW files.
To properly manage the color we need all elements
of software and hardware "understand" the image in the same way.
This plugin have 4 output purposes:
depending on what will be the destination of the image
we have to select a particular option.
This depends on the camera color profile,
the monitor profile and the printer you will print the photo.
Of these four, the perceptual method is the one that interests us:
the colors in the photo not available on the printer
will be changed to the more analogous available on the printer.
The options have other goals.
The colorimetric are typically used to print logos;
saturation is useful for graphics processing tables,
where it doesn't matter the hue but only the saturation of each color.
The following options are used to control the color space
containing the information of our photograph.
In Darktable, icc profiles are stored in a system folder.
sRGB is the safest for the web,
but has a limited color range compared to others
like AdobeRGB or Prophoto.
If our goal is to print, the lasts are more convenient,
and if the destination is to display on a monitor,
it is more convenient choose sRGB.
You can also control the display profiles.
Although it is a little strange that this plugin is in the color group,
being a technical tool,
it is essential to have this option to work accurately in our photos.
'Color contrast': this plugin works the color from another approach.
Unlike 'velvia' or 'channel mixer', working with RGB,
'color contrast' works in Lab.
Lab mode has a luminance channel (L) and two for colors,
dealing with green and magenta for channel 'a'
and blue and yellow for channel 'b'.
What is special working in Lab mode
is that we don't alter the brightness of the image.
On the other hand, what we get with the Lab can be so unexpected
and sometimes very aesthetic.
The change in the image is quite big,
but as you can see it fully respects the luminance information.
In photographs where it is not important to respect the color,
we can play with the color gamut by this plugin.
In this case, for example, I should keep the green color of the leaves,
but I can alter the color of the flower petals.
Overall this plugin works well decreasing the saturation,
rather than raising it.
Interesting effects can be achieved even in portraits.
By the way, I want to thank the request of one of the followers of this series
to make a video about blending modes.
I hope to have it finished soon and I invite everyone
to suggest other topics that I can share with you.
The following plugin is 'color correction'.
This plugin attempts to correct the color information
of the picture using a dye.
This is achieved in other programs by adding layers of color
and some particular blending modes.
In Dt is achieved by this curious interface,
it is a palette with a color gradient and a frame
that can be resized or moved over this color map.
The area inside the box
marks the range of colors that will be used for dyeing.
It doesn't have the accuracy
that could be achieved by introducing numerical data,
but it is a very simple way to quickly achieve this effect.
It has cooling and warming filters as presets.
We can also get other results by playing with blending modes.
Subtitles by Paulo C. Santos Garcia