Which workflow?


(Paul Deverson) #1

Hi,

I am new to open source software and wish to get my colour management as accurate as possible. I have settled on darktable and Gimp and have read up as much as I can on how to set them up. I’d be really interested to get the opinions on my workflow setup from those of you who have a lot more experience with these programs.

I use a MacBook running OS X 10.11.6 and have darktable 2.2.5 and Gimp 2.8.22. My main interest is putting images on the web.

I profiled my monitor using the Apple Display Calibrator Assistant and while I appreciate that it isn’t terribly sophisticated, it’s not an adjustable standalone monitor and actually, if I open a test image in Preview or in Gimp, it looks pretty good.

I profiled my camera, a Nikon D90, using the procedure outlined in Elle Stone’s excellent article on Profiling Your Digital Camera on her Nine Degrees Below website.

My settings are:

Darktable:
Input Color Profile: My Nikon D90 profile
Output Color Profile: sRGB-elle-V4-srgbtrc.icc (equivalent to the Gimp 2.8 working space)

Gimp:
RGB Profile: None
Monitor profile: sRGB IEC61966-2.1*

  • I’m using this because if I use my monitor profile, when I open a file in Gimp it looks the same as it did in darktable but when I export it to a jpeg and view it in Preview or on a website via a browser, it looks desaturated. If I use this profile, when I open the file in Gimp, it appears desaturated right away, then if I process it to look right, then it exports OK.

Is this what you would expect to happen? Am I using the settings to best advantage? Any ideas for improvement?


(Mica) #2

Hello and welcome!

Color management is quite difficult. If you’re primarily seeing the internet as your viewing platform, then sRBG is your best bet.

Your setting seem sound, however:

“Looking good” is not a proper test, calibration needs to be accurate, not look good.

The Apple calibration thing isn’t great, as it relies on your eyes. If you’re serious, buy or rent a hardware calibration unit. Split the cost with a friend in town or see if your local photo club has one.


(Morgan Hardwood) #3

By not using your monitor profile in GIMP, you’re not seeing correct colors and tones in GIMP. If you then tweak the image in GIMP to look better (curves, color changes, etc), you’re adjusting it to look better only on your not-color-managed monitor, but incorrect on every color-managed monitor and incorrect on every monitor which does show sRGB correctly.

You don’t need to use color management in GIMP if you, like me, only use GIMP to remove dust, fix stitching errors and do anything that doesn’t change the color or tones. But if you do touch any of the color and tone tools then you should use color management which requires a monitor profile.

This is all assuming that your monitor and camera profiles are correct and accurate.


(Paul Deverson) #4

Thanks for your reply, Morgan. If I were to select No Color Management in Gimp preferences, how would I set the other parameters on that page?


(Paul Deverson) #5

Thanks for your response. I do need to find a way to create a monitor profile.


(John) #6

I use raw therapee not dark table and also run Linux. Behaviour should be very similar. When I open an ex RT image in the GIMP it detects the profile RT uses in images and asks if keep or change to standard sRGB. I’d expect GIMP to behave the same way on all platforms if the image profile is not a standard sRGB. Essentially it is an sRGB package. RT happens to use an equivalent. Not sure why as the sRGB profile is not copyright protected and is free to use. So behaviour there should depend on what DT uses.

On Linux the GIMP will pick up and use a monitor profile automatically. It can also be selected via edit-preferences-colour management. Rendering intent can also be set their. You may find it defaults to absolute for display as there are no changes in output media and perceptual for softproofing. That can also be changed to the usual variations if needed.

There is an opensource display calibration utility called DisplayCal. It’s compatible with the majority of colorimeters and spectrometers. I’m not keen on display a series of images and adjust etc but a better set than most is on this site. One in particular should help you set brightness correctly or at least balance that up as well as it can be. That’s the one with all of the split squares maybe along with the first black point test.

https://www.drycreekphoto.com/Learn/Calibration/monitor_black.htm

The spiit square test is pretty extreme. What I have found is that monitors often don’t show a number of the splits at the dark end or the bright end. The black test is likely to show faintly at 5 or so but you may have to accept a number higher than that.

Some find DisplayCal difficult to use. It’s best to stick with it’s default settings initially. The important stage is the first one where on a normal monitor the brightness and colour channels are adjusted to get as close to 120 cd/m^2 and a colour temperature of 6500K. The important aspect is the error it shows = de. It needs to be as low as possible and that may mean departures from the ideal numbers. Give or take 100k isn’t going to make any significant difference really. Any contrast setting needs to be set to factory default. Personally I favour ColorMonki colorimeters. Some use Spiders. Even a used on is probably a better bet than not having one at all. Mac and Windows users can just stick with the software that comes with colorimeters

Not sure about laptops etc but all monitors are supplied way too bright these days as it makes the dynamic range numbers better. Most have adjustments going 0-100 as well rather than the old 0-255 which means they wont set so precisely.

One more thing. It’s not that unusual for Nikon users to stick with their raw development package initially and then export to another editor. The reason for this is down to how Nikon generate camera profiles so profiling the camera makes sense. :wink: Maybe I should put maybe after that.

John


(Flössie) #7

Please see RawPedia:

RT_sRGB is a higher quality version of the standard sRGB profile, which surprisingly is inconsistent between implementations. RT_sRGB was custom-made for RawTherapee by Jacques Desmis and has 4096 LUT points, as opposed to the lower quality 1024 point sRGB profiles. Applications that aren’t color managed and won’t take advantage of RT_sRGB will fall back on sRGB.

Best,
Flössie


(John) #8

Interesting. In that case as the vast majority of views of images will be assuming sRGB so if no differences why not use sRGB in the first place.

Not sure i understand the comments about sRGB profile variations on the web pages mentioned by the OP. I would assume that the profiles are available somewhere somehow around here

http://www.color.org/srgbprofiles.xalter

V4 and opensource may not fit in though so may have to be V2.

Not an area I know much about though so will have to try and fix that. I want people to see what I see when I edit shots. In the past I have allowed the GIMP to change the profile but not carefully studied any differences.

John


(John) #9

:rofl:Out of curiosity I converted an RT image to sRGB via loading and saving from the GIMP and then used exiftool to check for a profile. GIMP changed it to unmanaged display after spending a few seconds converting it. I’m laughing because some years ago I posted an image some where and was told by some one that there was no profile in it. This was presumably due to telling GIMP to convert.

Going on from that I thought ok but check what should be there. This is ex photoshop and uses the default sRGB profile from some one else’s photo.

Profile Class : Display Device Profile
Color Space Data : RGB
Profile Connection Space : XYZ
Profile Date Time : 1998:02:09 06:49:00
Profile File Signature : acsp
Primary Platform : Microsoft Corporation
CMM Flags : Not Embedded, Independent
Device Manufacturer : IEC
Device Model : sRGB
Device Attributes : Reflective, Glossy, Positive, Color
Rendering Intent : Media-Relative Colorimetric
Connection Space Illuminant : 0.9642 1 0.82491
Profile Creator : HP
Profile ID : 0
Profile Copyright : Copyright © 1998 Hewlett-Packard Company
Profile Description : sRGB IEC61966-2.1
Media White Point : 0.95045 1 1.08905
Media Black Point : 0 0 0
Red Matrix Column : 0.43607 0.22249 0.01392
Green Matrix Column : 0.38515 0.71687 0.09708
Blue Matrix Column : 0.14307 0.06061 0.7141
Device Mfg Desc : IEC http://www.iec.ch
Device Model Desc : IEC 61966-2.1 Default RGB colour space - sRGB
Viewing Cond Desc : Reference Viewing Condition in IEC61966-2.1
Viewing Cond Illuminant : 19.6445 20.3718 16.8089
Viewing Cond Surround : 3.92889 4.07439 3.36179
Viewing Cond Illuminant Type : D50
Luminance : 76.03647 80 87.12462
Measurement Observer : CIE 1931
Measurement Backing : 0 0 0
Measurement Geometry : Unknown
Measurement Flare : 0.999%
Measurement Illuminant : D65
Technology : Cathode Ray Tube Display
Red Tone Reproduction Curve : (Binary data 2060 bytes, use -b option to extract)
Green Tone Reproduction Curve : (Binary data 2060 bytes, use -b option to extract)
Blue Tone Reproduction Curve : (Binary data 2060 bytes, use -b option to extract)

The original discussion between MS and HP used to be about on the web. HP as I understand it came up with gamma - needed for mid tone contrast due to the log type response of the human eye.

Also read some of the content of the site mentioned by the OP. It’s an area that has interested me for a long time. Human sight comes into it and for the first time I have found a site that gives a decent over view of the “problems”. It usually takes 2 as sensitivity isn’t usually included. If interested in the subject of gamuts it’s worth a look and some thought about the implications. Where should the 3 colour primaries be for instance. There is no simple answer.

https://www.quora.com/Why-are-only-seven-colors-visible-to-the-naked-human-eye

John


#10

It would be interesting what version of GIMP you used. I’d also like to see the image you exported to check for the profile, too. Maybe there is some hint inside that might tell us what went wrong. I think I saw something similar when using GIMP’s internal sRGB. Using some external sRGB ICC profile works for me though.


(John) #11

Version 2.8.22. Image picked at random and exiftool used to view the original to check that RT’s profile was in it then loaded into the gimp, said ok to the conversion pop up and then just exported jpg with a different name and then used exiftool again to see what was in that. My version of GIMP is set to ask what to do when an image is loaded that contains a profile. As this is as installed I’d guess it’s the default. It offers keep it or convert to RGB workspace as well as ask. An RGB profile can be selected in a separate section of colour management. It picked up my monitor profile all by itself.

Maybe if an RGB profile is set it will then add it to images when they are exported. I think KDE comes with a number of profiles but off hand can’t remember which ones.

As far as browsers are concerned - the usual method people often use to view other peoples image colour management is partial in some respects. Try them on this page

http://www.color.org/browsertest.xalter

The following page uses images instead and shows that within reason it works but also shows what happens with prophoto and why it’s best to save as sRGB instead. Some reckon that is always the safest option if they can work or even view in other colour spaces.

John