You may have heard that Krita has something called color-management. Or maybe you just wondered what all these 'color model' and 'color profile' things you can find in the menus mean. Color management is pretty useful for people who work in digital imaging professionally, and hopefully this page will explain why.
If you've never worked with color management before, and have no clue what it is, then know that you've probably been working in the 8bit RGB color space with the sRGB profile. This means you can choose for sRGB built-in or sRGB-elle-v2-srgbtrc.icc. With the new color space browser this profile is marked with (default) when using 8bit.
We'll go into what these terms mean in the theory, but if you're here only for trying to figure out which is the default, you now know it. Maybe, after reading this, you may feel like changing the default, to get new and interesting results from filters, blending modes, or just the color smudge brush.
To explain the point of color management, you'd first need to learn which problem color management tries to solve.
Let us imagine a kindergarten:
The class of 28 children is subdivided in groups of 7. Each group has their own table.
The teacher gives them a painting assignment: They need to paint a red triangle, a blue square, a green circle and put a yellow border around the three. The kids are very experienced with painting already, so the teacher can confidently leave the smarter ones to their own devices, and spent more time on those who need help.
The following results come from painting:
Even though all groups had the same assignment, each group's result looks different.
Group 1 had vermillion red, citron yellow and ultramarine blue to their disposal. This means their triangle looks nice and red, but their circle's green is muddy. This is because ultramarine is too dark of a blue to create nice greens with.
Group 2 had magenta red, citron yellow and cerulean blue. Magenta is a type of red that is closer to pink, opossed to vermillion, which is closer to orange. However, their green looks nice because cerulean is a much lighter blue.
Group 3 had vermillion red, citron yellow, edmerald green and cerulean blue. They didn't mix their green, and thus ended up with a purer color.
Finally, group 4 has Vermillion red, citron yellow and cerulean blue. Their colors probably look like what you imagined.
Now, these are kindergarteners, so this isn't the largest problem in the world. However, imagine that something like this happened at a printing company? Imagine four printers printing the same magazine with wildly different results? That would be disastrous!
For this purpose, we invented color management.
Color management is, dryly put, a set of systems that tries to have the same color translate properly between color devices.
It usually works by attempting to covert a color to the reference color space XYZ. XYZ is a coordinate system that has a spot for all colors that the average human eye can see.
From XYZ it can then be translated back into another device space, such as RGB(for screens), or CMYK(for printers).
Krita has two systems dedicated to color management. On one hand we have lcms2, which deal with Icc-profiles, and on the other we have OCIO, which deal with LUT color management.
To give a crude estimate, ICC profiles deal with keeping colors consistent over many interpretations of devices(screens, printers) by using a reference space, and OCIO deals with manipulating the interpretation of said colors.
Within both we can identify the following color spaces:
Knowing this about these spaces of course doesn't give you an idea how to use them, but it does make it easier to explain how to use them. So let us look at a typical color management workflow:
In a traditional color managed workflow, we usually think in terms of real world colors being converted to computer colors and the other way around. So, for example photos from a camera or scanned in images. If you have a device space of such a device, we first assign said device space to the image, and then convert it to a working space.
We then do all our editing in the working space, and use the working space to communicate between editing programs. In Krita's case, due to it having two color management systems, we use ICC profiles between programs like Gimp 2.9+, Inkscape, Digikam and Scribus, and OCIO configuration between Blender and Natron.
You also store your working files in the working space, just like how you have the layers unmerged in the working file, or have it at a very high resolution.
Sometimes, we apply aesthetic or 'look' spaces to an image as part of the editing process. This is rather advanced, and probably not something to worry about in Krita's case.
Then, when we're done editing, we try to convert to an output space, which is another device space. This can be CMYK for printers or a special screen RGB profile. When you are dealing with professional printing houses, it is best to ask them about this step. They have a lot of experience with doing the best conversion, and may prefer to do the conversion from your working space to the device space of their printers.
Another form of output is the way your screen displays the color. Unlike regular output, this one is done all the time during editing: After all, you need to be able to see what you are doing, but your screen is still a device with a device space, so it does distort how the image looks. In this manner, you can see your screen as a set of binoculars you have to look through to see your image at all.
Therefore, without a profiled monitor, you actually don't know what the actual colors you are working with are like, because the computer doesn't know the relevant properties of your screen. So if you profiled your monitor, give Krita the profile in the settings, and select the sRGB space to draw in, you are for the first time seeing the actual colors of the sRGB space.
Now, photographers and people who do a tricky discipline of VFX called 'color grading' will go completely mad over trying to get the colors they put in to come out 100% correctly, and will even count in factors like the time of day and the color they painted their walls. For example, if the wall behind your computer is pure red, your eyes will adjust to be less sensitive to red, which means that the colors they pick in the program could come out redder. We call these the viewing conditions.
Thankfully, artists have to worry a slight bit less about this. As illustrations are fully handmade, we are able to identify the important bits and make appropriate contrasts between colors. This means that even if our images turn out to be slightly redder than intended, it is less likely the whole image is ruined. If we look back at the kindergarten example above, we still understand what the image was supposed to look like, despite there being different colors on each image. Furthermore, because the colors in illustrations are deliberately picked, we can correct them more easily on a later date. Yet, at the same time, it is of course a big drag to do this, and we might have had much more flexibility had we taken viewing conditions under consideration.
That said, for artists it is also very useful to understand the working spaces. Different working spaces give different results with filters and mixing, and only some working spaces can be used for advanced technology like HDR.
Similarly, Krita, as a program intended to make images from scratch, doesn't really worry about assigning workspaces after having made the image. But because you are using the screen as a binocular to look at your image, and to pick colors, you can see your screen's device space as an input space to the image. Hence why profiling your monitor and giving the profile to Krita in the settings can help with preparing your work for print and future ventures in the long run.
Overall, it is kinda useful to keep things like viewing conditions in the back of your mind. Many professional artists use a mid-grey color as their default canvas background because they find they create much more dynamic images due to having improved their viewing conditions. It is also why a lot of graphics programs, including Krita, come with a dark theme nowadays. (Though, of course this might also be because dark themes can be considered cool, who knows.)
We go over the type of pitfalls that are specific to artists painting from scratch in the viewing conditions section, but let's first take a look at our color management systems.
An Icc profile is a set of coordinates describing the extremities of the device space within XYZ, and it is the color management data you use to communicate your working space to printers and applications that are designed for the print industry, such as GIMP, Scribus, Photoshop, Illustrator, Inkscape, Digikam, RawTheraphee, etc. You have two types of icc profiles:
The interesting thing about icc profiles is that your working space can be larger than your device space. This is generally not bad. However, when converting, you do end up with the question of how to translate the working space values.
ICC profile version is the last thing to keep in mind when dealing with ICC profiles. Krita delivers both Version 2 and Version 4 profiles, with the later giving better results in doing color maths, but the former being more widely supported (as seen below in 'interoperability with other programs'). This is also why Krita defaults to V2, and we recommend using V2 when you aren't certain if the other programs you are using support V4.
The LUT Docker is the second important bit of color management in Krita that is shared between Krita and programs like Blender, Natron and Nuke, and only uses Look Up Tables that are configured via a config file.
You can set the workingspace of the image under input color space, and the display to sRGB or your own LUT if you have added it to the config. View in this case is for proofing transforms to a certain display device.
Component, exposure, gamma, whitepoint and blackpoint are knobs which allows you to modify the display filter.
As explained before, we can see our monitor as a telescope or binocular into the world of our picture. Which means it distorts our view of the image a little. But we can modify this binocular, or display filter to see our image in a different way. For example, to allow us to see the white in an image that are whiter than the white of our screen. To explain what that means, we need to think about what white is.
For example, white, on our monitor is full red, full green and full blue. But it's certainly different from white on our paper, or the color of milk, white from the sun, or even the white of our cell-phone displays.
Black similarly, is brighter on a LCD display than a LED one, and incomparable with the black of a carefully sealed room.
This means that there's potentially blacker blacks than screen black, and white whites than screen white. However, for simplicity's sake we still assign the black-point and the white-point to certain values. From there, we can determine whether a white is whiter than the white point, or a black black than the black-point.
The LUT docker allows us to control this display-filter and modify the distortion. This is useful when we start modifying images that are made with scene referred values, such as HDR photos, or images coming out of a render engine.
So, for example, we can chose to scale whiter-than-screen-white to our screen-white so we can see the contrasts there.
The point of this is that you can take advantage of more lightness detail in an image. While you can't see the difference between screen white and whiter-than-screen-white(because you screen can't show the difference), graphics programs can certainly use it.
A common example is matching the lighting between a 3d model and a real world scene. Others are advanced photo retouching, with much more contrast information available to the user. In painting itself, this allows you to create an image where you can be flippant with the contrast, and allow yourself to go as bright as you'd like.
LUT docker manipulations are per view, so you can create a new view and set it to luminosity. This way you can see the image in both color as well as grayscale and keep a good eye on your values.
Another example is to carefully watch the gradients in a certain section.
Like Icc, the LUT Docker allows you to create a profile of sorts for your device. In this case it's the 'lut', which stands for 'Look Up Table', and which can be added to OCIO by modifying the config file.
Now, the situation we talked about above is what we would call 'linear'. Each step of brightness is the same value. Our eyes do not perceive linearly. Rather, we find it more easy to distinguish between darker greys than we do between lighter greys.
As humans are the ones using computers, we have made it so that computers will give more room to darker values in the coordinate system of the image. We call this 'gamma-encoding', because it is applying a gamma function to the TRC or transfer function of an image. The TRC in this case being the Tone Response Curve or Tone Reproduction Curve or Transfer function (because color management specialists hate themselves), which tells your computer or printer how much color corresponds to a certain value.
The following table shows how there's a lot of space being used by lighter values in a linear space compared to the default sRGB trc of our modern computers and other TRCs available in our delivered profiles:
|Lab L* TRC|
|Rec 709 TRC|
|Gamma 1.8 TRC|
|Gamma 2.2 TRC|
If you look at linear of rec 709 TRCs, you can see there's quite a jump between the darker shades and the lighter shades, while if we look at the Lab L* TRC or the sRGB TRC, which seem more evenly spaced. This is due to our eyes' sensitivity to darker values. This also means that if you do not have enough bit depth, an image in a linear space will look as if it has ugly banding. Hence why, when we make images for viewing on a screen, we always use something like the LAB L*, sRGB or Gamma 2.2 TRCs to encode the image with.
However, this modification to give more space to darker values does lead to wonky color maths when mixing the colors.
We can see this with the following experiment:
Red circle and blue circle over grey, half blurred. In a gamma-corrected environment, this gives an odd black border. In a linear environment, this gives us a nice gradation.
This also counts for Krita's color smudge brush:
Imagine we want to mix red and green.
First, we would need the color coordinates of red and green inside our color space's color model. So, that'd be...
We then average these coordinates over three mixes:
But to figure out how these colors look on screen, we first put the individual values through the TRC of the color-space we're working with:
Then we fill in the values into the correct spot. Compare these to the values of the mixture table above!
|Linear TRC||sRGB TRC||Lab L* TRC||Rec 709 TRC||Gamma = 1.8 TRC||Gamma = 2.2 TRC|
And this is why color mixtures are lighter and softer in linear space. Linear space is more physically correct, but sRGB is more efficient in terms of space, so hence why many images have an sRGB TRC encoded into them. In case this still doesn't make sense: sRGB gives largely darker values than linear space for the same coordinates.
So different TRCs give different mixes between colors, in the following example, every set of gradients is in order a mix using linear trc, a mix using srgb trc and a mix using lab L* trc.
So, you might be asking, how do I tick this option? Is it in the settings somewhere? The answer is that we have several icc profiles that can be used for this kind of work:
In fact, in all the 'elle'-profiles, the last number indicates the gamma. 1.0 is linear, higher is gamma-corrected and 'srgbtrc' is a special gamma correction for the original sRGB profile.
If you use the color space browser, you can tell the TRC from the 'estimated gamma' (if it's 1.0, it's linear), or from the TRC widget in Krita 3.0, which looks exactly like the curve graphs above.
Even if you do not paint much but, for example, you are making textures for a video game or rendering, using a linear space is very beneficial and will speed up the renderer a little, since it won't have to convert images on its own.
The downside of linear space is of course that white seems very overpowered when mixing with black, because in a linear space, light grays get more room. In the end, while linear space is physically correct, and a boon to work in when you are dealing with physically correct renderers for videogames and raytracing, Krita is a tool and no-one will hunt you down for preferring the dark mixing of the sRGB trc.
Using Krita's color space browser, you can see that there's many different space sizes.
How do these affect you image, and why would you use them?
The three primary reasons to use a large space:
Let's compare the following gradients in different spaces:
On the left we have an artifact-ridden color managed jpeg file with an ACES sRGBtrc v2 profile attached (or not, depending on mediawiki's mood, if not then you can see the exact different between the colors more clearly). This should give an approximation of the actual colors. On the right, we have a sRGB png that was converted in Krita from the base file.
Each of the gradients are gradients from the max of a given channel. As you can see, the mid-tone of the ACES color space is much brighter than the mid-tone of the RGB colorspace, and this is because the primaries are further apart.
What this means for us is that when we start mixing or applying filters, Krita can output values higher than visible, but also generate more correct mixes and gradients. In particular, when color correcting, the bigger space can help with giving more precise information.
If you have a display profile that uses a LUT, then you can use perceptual to give an indication of how your image will look.
Bigger spaces do have the downside they require more precision if you do not want to see banding, so make sure to have at the least 16bit per channel when choosing a bigger space.
We mentioned viewing conditions before, but what does this have to do with 'white points'?
A lot actually, rather, white points describe a type of viewing condition.
So, usually what we mean by viewing conditions is the lighting and decoration of the room that you are viewing the image in. Our eyes try to make sense of both the colors that you are looking at actively (the colors of the image) and the colors you aren't looking at actively (the colors of the room), which means that both sets of colors affect how the image looks.
This is for example, the reason why museum exhibitors can get really angry at the interior decorators when the walls of the museum are painted bright red or blue, because this will drastically change the way how the painting's colors look. (Which, if we are talking about a painter known for their colors like Vermeer, could result in a really bad experience).
Lighting is the other component of the viewing condition which can have dramatic effects. Lighting in particular affects the way all colors look. For example, if you were to paint an image of sunflowers and poppies, print that out, and shine a bright yellow light on it, the sunflowers would become indistinguishable from the white background, and the poppies would look orange. This is called metamerism, and it's generally something you want to avoid in your color management pipeline.
Examples where metamerism could become a problem is when you start matching colors from different sources together.
For example, if you are designing a print for a red t-shirt that's not bright red, but not super grayish red either. And you want to make sure the colors of the print match the color of the t-shirt, so you make a dummy background layer that is approximately that red, as correctly as you can observe it, and paint on layers above that dummy layer. When you are done, you hide this dummy layer and sent the image with a transparent background to the press.
But when you get the t-shit from the printer, you notice that all your colors look off, mismatched, and maybe too yellowish (and when did that T-Shirt become purple?).
This is where white points come in.
You probably observed the t-shirt in a white room where there were incandescent lamps shining, because as a true artist, you started your work in the middle of the night, as that is when the best art is made. However, incandescent lamps have a black body temperature of roughly 2300-2800K, which makes them give a yellowish light, officially called White Point A.
Your computer screen on the other hand, has a black body temperature of 6500K, also known as D65. Which is a far more blueish color of light than the lamps you are hanging.
What's worse, Printers print on the basis of using a white point of D50, the color of white paper under direct sunlight.
So, by eye-balling your t-shirt's color during the evening, you took it's red color as transformed by the yellowish light. Had you made your observation in diffuse sunlight of an overcast (which is also roughly D65), or made it in direct sunlight light and painted your picture with a profile set to D50, the color would have been much closer, and thus your design would not be as yellowish.
Now, you could technically quickly fix this by using a white balancing filter, like the ones in G'MIC, but because this error is caught at the end of the production process, you basically limited your use of possible colors when you were designing, which is a pity.
Another example where metamerism messes things up is with screen projections.
We have a presentation where we mark one type of item with red, another with yellow and yet another with purple. On a computer the difference between the colors are very obvious.
However, when we start projecting, the lights of the room aren't dimmed, which means that the tone scale of the colors becomes crunched, and yellow becomes near indistinguishable from white. Furthermore, because the light in the room is slightly yellowish, the purple is transformed into red, making it indistinguishable from the red. Meaning that the graphic is difficult to read.
In both cases, you can use Krita's color management a little to help you, but mostly, you just need to be aware of it, as Krita can hardly fix that you are looking at colors at night, or the fact that the presentation hall owner refuses to turn off the lights.
That said, unless you have a display profile that uses LUTs, such as an OCIO lut or a cLUT icc profile, white point won't matter much when choosing a working space, due to weirdness in the icc v4 workflow which always converts matrix profiles with relative colorimetric, meaning the white points are matched up.
Bit depth basically refers to the amount of working memory per pixel you reserve for an image.
Like how having a A2 paper in real life can allow for much more detail in the end drawing, it does take up more of your desk than a simple A4 paper.
However, this does not just refer to the size of the image, but also how much precision you need per color.
To illustrate this, I'll briefly talk about something that is not even available in Krita:
However, this is not available in Krita. Krita instead works with channels, and counts how many colors per channel you need. This is called 'real color'.
This is important if you have a working color space that is larger than your device space: At the least, if you do not want color banding.
And while you can attempt to create all your images a 32 bit float, this will quickly take up your RAM. Therefore, it's important to consider which bit depth you will use for what kind of image.
Krita has two modes of color management:
Krita does a lot of color calculations, often concerning the blending of colors. These color calculations works best in linear color space, and linear color space requires a bit depth of at the least 16 bit to work correctly. The disadvantage is that linear space can be confusing to work in.
If you like painting, have a decent amount of RAM, and are looking to start your baby-steps in taking advantage of Krita's color management, try upgrading from having all your images in sRGB built-in to sRGB-v2-elle-g10.icc or rec2020-v2-elle-g10.icc at 16 bit float. This will give you better color blending while opening up the possibility for you to start working in hdr!
|Some graphics cards, such as those of the Nvidia-brand actually have the best performance under 16bit float, because Nvidia cards convert to floating point internally. When it does not need to do that, it speeds up!|
|No amount of color management in the world can make the image on your screen and the image out of the printer have 100% the same color.|
When you finished you image and are ready to export it, you can modify the color space to optimize it:
If you are preparing an image for the web:
|In some versions of Firefox, the colors actually look strange: This is a bug in Firefox, which is because it's color management system is incomplete, save your png, jpg or tiff without an embedded profile to work around this.|
If you are preparing for print:
If you wish to use Krita's OCIO functionality, and in particular in combination with Blender's color management, you can try to have it use Blender's OCIO config.
Blender's OCIO config is under <Blender-folder>/version number/datafiles/colormanagement. Set the LUT docker to use the OCIO engine, and select the config from the above path. This will give you Blender's input and screen spaces, but not the looks, as those aren't supported in Krita yet.
You might encounter some issues when using different applications together. One important thing to note is that the standard Windows Photo Viewer application does not handle modern ICC profiles. Krita uses version 4 profiles; Photo Viewer can only handle version 2 profiles. If you export to JPEG with an embedded profile, Photo Viewer will display your image much too dark.
Here are some example workflows to get a feeling your color management workflow.
As mentioned before, input for your screen is set via settings->configure Krita->color management, or via the LUT docker's 'screen space'. Working space is set via new file per document, or in the LUT docker via 'input space'.
Use the sRGB-elle-V2-srgbtrc.icc for going between inkscape, photoshop, painttool sai, illustrator, Gimp, mypaint, mangastudio, paintstorm studio, mypaint, artrage, scribus, etc. and Krita.
If you are using a larger space via ICC, you will only be able to interchange it between Krita, Photoshop, Illustrator, GIMP 2.9, Manga Studio and Scribus. All others assume sRGB for your space, no matter what, because they don't have color management.
If you are going between Krita and Blender, Nuke or Natron, use OCIO and set the input space to 'sRGB', but make sure to select the sRGB profile for icc when creating a new file.
For the final for the web, convert the image to sRGB 8 bit, srgbtrc, do not embed the icc profile. Then, if using png, put it through something like pngcrush or other png optimisers. sRGB in this case is chosen because you can assume the vast majority of your audience hasn't profiled their screen, nor do they have screens that are advanced enough for the wide gamut stuff. Hence we convert to the screen default for the internet, sRGB.
The CMYK profiles are different per printer, and even per paper or ink-type so don't be presumptuous and ask ahead for them, instead of doing something like trying to paint in any random CMYK profile. As mentioned in the viewing conditions section, you want to keep your options open.
You can set the advanced color selector to transform to a given profile via settings->configure Krita->advanced color selector settings. There, tick 'color selector uses a different color space than the image' and select the CMYK profile you are aiming for. This will limit your colors a little bit, but keep all the nice filter and blending options from RGB.
So this one is tricky. You can use OCIO and ICC between programs, but recommended is to have your images to the engine in sRGB or grayscale. Many physically based renderers these days allow you to set whether an image should be read as a linear or srgbtrc image, and this is even vital to have the images being considered properly in the physically based calculations of the game renderer.
While game engines need to have optimised content, and it's recommended to stay within 8 bit. Future screens may have higher bit-depths. When renderers start supporting higher bit-depths, it may be beneficial to develop a workflow where the working-space files are larger-than-currently-needed and you run some scripts to optimise them for your current render needs. The larger working-space files make updating the game in the future for fancier screens less of a drag.
Normal maps and heightmaps are officially supossed to be defined with a 'non-color data' working space, but you'll find that most engines will not care much for this.
Specular, glossiness, metalness and roughness maps are all based on linear calculations, and when you find that a certain material has a metalness of 0.3, this is 30% gray in a linear space. Therefore, make sure to select a linear space to work in, and to tell the renderer that this is a linear space image.