Contents. Colorimetry concepts This document aims at several objectives about colorimetry: 1.
![Rgb Rgb](http://i96.photobucket.com/albums/l190/wbassett/Munsell/Munsell_N7.jpg)
To summarize the raw file processing pipeline from a colorimetry point of view and to highlight key points and gaps 2. To explain the main steps principles in order to allow the user to be able to weight what is at stake.
To explain the use of some functions that may look obscure to newcomers. Note: This document only deals with RawTherapee 4 and computing with real numbers, and not RawTherapee 3. More over it does not take into account possible malfunctioning (bugs) still unsolved! Warning. This document doesn't aim to deal with the whole colorimetry aspects that aren't specific to RawTherapee, like for instance:.
the printing,. screens calibration. However, it is recommended to calibrate the screens with one of the many products in the market: colorimetric probe plud software. The created profile is for the monitor only and must never, in any case, be used either as input profile or output profile. Under Windows, MacOS or Linux, a software like DispalGUI from Argyll, combined with a probe of quality, even old (e.g. The DTP94 probe I own, and for which it doesn't exist any more ?? drivers for Windows) give very good results; the processing time is quite long (about an hour).
RawTherapee automatically detects the system profile, however you can enter the screen icc filename in « Preference/ Color Management / Monitor Profile ». The reader shall preferably have minimal knowledges about color management: matrix triplet, RGB, XYZ, Lab, color space, primaries and colorimetric profile. Wise readers can read the B. Lindbloom's website. The histogram display as well as the browser can be configured: by default, the displayed values take into account the 'Output profile'.
You can change this behaviour going into 'Preferences' and checking 'Use working profile for main histogram and navigator'. Of course, this document is far to be exhaustive, the subject is complex. Initial raw processing before RGB conversion Read the raw file and use its data.
Le first step that is essentially carried out on a Dcraw basis (thanks to D.Coffin) consists in reading all types of raw files, with their proprietary coding: data depth, 12 or 14 bits, sensor saturation, white balance. And of course rggb or rgbg data;. the default white balance is the one chosen by the user on his/her camera for the shooting!. the interpolation (AMaZE, AHD, DCB.) takes place after by rgb data modifying (the image can be visually evaluated on a screen): the interpolation shouldn't modify the colorimetry (or a very few) and that is the case for all the existing interpolations in RawTherapee (deltaE94 due to interpolation is approximatively 1, so negligible), in the other hand, at the limits (upper highlights.) artefacts may appear for some of them. Test pattern 468 colors, for calibration. shoot a test pattern in ideal conditions matching the planned use (outside, studio.);.
Jan 30, 2012 - Currently listed Munsell colors: 10YR, 7.5YR and plenty more to come! Your conversion chart is not quite identical to what I've found.
the wider the test pattern gamut is, the better the result is, e.g. The ColorChecker24 is close to sRGB, even if it gives good results in usual cases, how could it efficiently evaluate real colors that are out sRGB range (flowers, artificial colors.)?. the higher is the test pattern cells number, better the result is (better profile guiding). The 468 colors test pattern, designed with a colleague 'Rouli', is over WideGamut for some colors, and owns low luminance values. On this graphic, we can see that for a same temperature, the Daylight 4000 illuminant (continuous spectre) is very different from Fluorescent F11 (4000K)., so, it will give a different colors rendering. Actually, the white balance calculates on the spectral data basis, two coefficients xD, yD that modify the channels multipliers: this calculation acts as an averaged integral calculus.
Indeed, the 'average' white balance will be exact, but the spectral data peaks or gaps, compared with a theoretical ideal (blackbody or daylight) will locally bring, for some colors, hue gaps more or less important. It exists a concept called 'CRI = Color Rendering Index' that translates the lighting source quality. This 'CRI' is a number equal to 100 for a perfect source. We consider that values over 90 give good results. E.g.:. Fluo F4 'warm white': CRI=51. Clear Mercury Vapor: CRI=17.
several LED with 'CRI' between 50 and 96. Solux 4700: CRI=92. etc.
This concept is embedded (not used yet) in RawTherapee with the following choices:. 20 reference colors of which, 8 'standard' from the Colorchecker24, 4 skin hues, 4 greys (white-black), 3 blues. use of CIECAM02 for the chromatic adaptation. use of CIE Lab for deltaE calculation To remedy it (partially) it is enough to create an with the desired lighting source and the matching spectral data. Other illuminants Other illuminants exist, stemmed from the A illuminant and close to 'Daylight'. B and C that I did not embedded in RawTherapee, but it is possible to do it. an illuminant with equal energy: 'E'.
The studio bulbs illuminants (movies, stage lighting, museums, photo studio, etc.) that are named HMI, GTI, Solux 4700K, JudgeIII, Solix4100K, Solux3500K, etc., they are embedded in RawTherapee. The LED illuminant, these lamps often have large gaps in the blues. Some of them own very satisfactory features.
'Proprietary' flashes illuminants (Canon, Nikon, Pentax.) and studio flashes illuminants, they are generally very close to daylight, but each one at different temperatures. I did several grouping at 5500K, 6000K et 6500K, about studio flashes, it should be useful to have their features: a) theoretically it should be useful to have the spectral data for each flash (I don't have them), moreover, these data vary depending on the flash power.; b) so, I preferred to use the equivalent 'daylight'. As we can see, the situation is not simple and pose many problems to the raw processing software, of which RawTherapee. Illuminants Diagrams and Color Rendering Index (CRI). Colors drifts representation for L=70 Output space 'Output Profile' Space choice The first thing to examine is: what are the output profiles that are installed on your computer?
This depends of: a) the operating system (on the face of it, Linux does not install any profile); b) the other graphical software that are installed (Capture NX2, PhotoShop CS, DxO, etc.), each one install proprietary profiles, for example NX2 installs some NKsRGB.icm NkAdobe.icm, etc. That are copyrighted.; c) profiles that you can have downloaded on the web, for example on the Adobe or B.Lindbloom websites. On principle I would recommend to check the installation or to install the output profiles matching the working profiles - that are.icm or.icc files physically present on your computer and that have nothing to do with the calculation matrix of 'iccmatrices.h'.
If these files are missing, TIFF or JPEG output cannot be done towards these profiles, but will be by default (if the RTsRGB.icm file is present) done towards the SRGB output space. These profiles have the following names (we can find others that have the same features or close features), they are generally copyrighted and consequently cannot be shipped with an Open Source software without authorization. They are available on the Web: ProPhoto.icm; SRB Color Space profile.icm; AdobeRGB1998.icc; BestRGB.icm; BetaRGB.icc; Bruce.icm; WideGamutRGB.icc. Of course you can install some others like CIE.icc; Colormatch.icc; etc. They must be installed in the RawTherapee 'Iccprofiles/output' folder or in windows system32 spool drivers color for Windows and /usr/share/color/icc for the other systems. When you choose an output profile, e.g. AdobeRGB1998 and the working profile Prophoto, LCMS2 will convert with a (chosen by default in the RawTherapee options: relative, perceptual.) the RGB data from the working space to the output space.
Gamut for a luminance L=95 Of courses, remarks about the choice of the output color space are similar to the ones about the working space (print, screen.). It you want to print with a high quality ink-jet printer (remind: RawTherapee has no print module so far), you have to use a third party software (Photoshop.), in this case I strongly recommend an output profile of Prophoto or WideGamut type. Take care however, JPG outputs, therefore 8 bits, are almost incompatible - important risk of posterization - with wide gamut spaces (Prophoto, WideGamut.). Shipped files Because of the copyrights, I shipped specific files with more detailed LUT that should bring less posterization in the shadows. Output sRGB gamma=2.3 slope=8 How to use it? To satisfy a desire for simplicity, the Output profile will be a derivative of the Working profile, the box Output profile appear in grey. That means Output profile = Working profile.
![Rgb To Munsell Converter Weight Rgb To Munsell Converter Weight](http://www.safetronics.sk/files/ral-pantonnem.jpg)
For instance, you select Working profile = Prophoto and Free gamma = 2.1 and slope =4.0. Then you validate a TIF output or towards the editor and you generate an output TIF file, with Prophoto profile and gamma 2.1 / 4.0. To open the file in an external editor (e.g.
Photoshop CS), it will appear 'Prefer the embedded profile: sRGB IEC61966-2.1 (RTH gamma BT709 similar to HP sRGB)' that match to the RTsRGBgBT709 profile but with a modification that we will examine further. Other example, you select Working profile = sRGB and Free gamma=2.3 and slope=10.0, you are going to generate a TIFF with sRGB and gamma 2.3 and slope=10 output. To open the file in an external editor (e.g. Photoshop CS), it will appear 'Prefer the embedded profile: sRGB IEC61966-2.1 (RTH gamma BT709 similar to HP sRGB)' that match to the RTsRGBgBT709 profile but with a modification that we will examine further. If you enable the option (Photoshop CS): 'Delete the embedded profile', the TIFF file will appear with the new RGB values due to the new gamma and slope values, but the image look will be different (file headers missing). The algorithm uses the LCMS function 'CMSToneCurve':.
the output spaces are computed from their primary (red, green, blue), e.g. For Prophoto: p1=0.7347; p2=0.2653; p3=0.1596; p4=0.8404; p5=0.0366; p6=0.0001;. the gamma parameters are computed with the 'calcgamma' function that will, accordingly with the gamma and the slope, determine 5 parameters to give to the LCMS2 right function.
So, we create a pseudo-profile, kind of RGB 'Prophoto' and with a gamma matching the selected one. But we find here, a LCMS2 gap, which creating this profile, does not write the matching profile in the file header, because it works with RGB values and not with LUT / Lab.
Theoretically, it should need as much profiles with an adapted gamma and not only one. In practice, I brought a large modification to Output Gamma and worked around the LCMS2 gap, by applying - after the RGB conversion, a profile.icc that has the same features that the.icc or.icm profiles used by Output Gamma but where the rTRC, gTRC, bTRC tags are computed with 'calcgamma'. To improve the understanding of the TIF processing in linear mode, you can read the Dcraw tutorial from Guillermo Luijk From which the necessity to have in the 'Iccdirectory' folder, the '.icc' and '.icm' files: BestRGB.icm; BetaRGB.icc; Bruce.icm; WideGamutRGB.icc, (and thus the icc/icm files added for the pseudo-Prophoto, Adobe, SRGB in 'Iccprofile/output'). RawTherapee profiles quality The user can ask himself with reason what is the RawTherapee profiles validity (RTsRGB, RTLarge.)?
These profiles have the same features that the 'original' ones (AdobeRGB1998, Prophoto, SrGB Color Space Profile), there is only small differences at the primaries and/or white point level. They do not have any incidence on output quality and level. In the other hand, TRC have more detailed LUT going from 1024 points to 4096 points. This has for consequence - in the sRGB case that is the more frequent output - a histogram with much less fish bones that may bring posterization in the shades. Here is for comparison with the same image, a 16 bits histogram enlargement in low lights, between sRGB Color Space profile and RTsRGB.