Pages: [1]   Go Down

Author Topic: ColorMunki Profile refinement  (Read 3487 times)

keith_cooper

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 473
    • Northlight Images
ColorMunki Profile refinement
« on: April 28, 2008, 07:37:37 am »

While I'm still waiting to be able to test this functionality in more detail, I've been checking up on the profile refinement option in the ColorMunki software.

Since several people have asked me about it I thought I'd post what I'd found out from some limited personal testing and talking with people at X-Rite (thanks).

How it works... ;-)

The first 50 patches are always the same set of device recipes (RGB or CMYK values).

With measurements from the first 50 patches, ColorMunki builds a profile and then runs a known set of Lab values (containing neutrals, skin tones, etc.) through the profile to determine roughly the device values of those desired colours.

This data is used to build the second target (which explains why the 2nd targets look quite similar)

Next, print and measure the newly created second target and then build the final profile using both sets of device recipe and measurement data.

This refinement process helps identify exactly where these key colour areas reside in the printer gamut.

In previous methods, it wasn't known which combination of device recipes actually printed neutral tones so more combinations of colours were printed/measured to find out.

The new iterative discovery process helps find these neutrals much more easily with fewer colour patches.

This is the key to the low patch count profiles but does depend on predictable behaviour of the printer in regions not sampled in the first set of patches.  This predictability is both a strength and potential weakness in the ColorMunki technique - I guess we'll have to wait for more people to do detailed testing, however you can bet that the algorithms have been tested on a lot of real world printers.

The image based optimisation works the same way as the second set of 50 patches.

The CM software automatically extract colours from the image, converts them to Lab (using the source / image profile)

The new target is then printed and measured. This information is then added to the previous measurement data set, and used to build a new profile.

Using this method, more information is gained about the printer's behaviour in the colour regions that were extracted from the refinement image.

The idea is that, next time you print an image using the new profile, the results will be even more colour accurate.

Because the process uses colours extracted from the image in this process, you can improve any colour region you want by using an image that contains those colours.

Since the process just adds additional pairs of device recipes and corresponding measured Lab values into the profile data set, it is a non-destructive process and can be repeated as many times as needed without damaging the profile.

Note that like with any profile building, this is subject to accurate measurements.
Remember as with many things 'Garbage in - garbage out'. This is one reason I'd want to give refined profiles a new name, since a duff set of measurements (one blocked nozzle for example) will mess up your profile and there is no easy way to undo things.

One area I'm curious to look at, is to see how well the CM profiles handle greyscale images, although it should be noted that there are no profile refinement options (such as true greys or paper relative greys) so it is a case of you get what you get. As ever, take this in context of the target market of the device - if you know of the difference about the greys, then you are in the ColorMunki 'Super Expert' category ;-)
Logged
bye for now -- Keith
[url=http://www.nor

Scho

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 95
    • http://photos.schophoto.com/
ColorMunki Profile refinement
« Reply #1 on: April 28, 2008, 10:23:11 am »

I was told that new software might be available this week, but that line has been used before.  

I tried optimizing a profile by feeding the current software (1.0) a 100 step grayscale target image.  Unfortunately, I couldn't see any difference in prints made with the original and optimized profiles.  Both exhibited magenta/green color crossovers and banding in smooth grayscale gradients and both exhibited strong metamerism.  Typical Epson driver performance with RGB profiles using MIS K4 inks in an Epson 4000.  The ColorMunki makes very nice profiles for color printing, but don't get your hopes up that this optimization routine will do much to improve grayscale printing using the Epson driver with RGB profiles.  Epson ABW, QTR, ColorBurst RIP, etc. are really better options for serious grayscale printing.

Quote
While I'm still waiting to be able to test this functionality in more detail, I've been checking up on the profile refinement option in the ColorMunki software.

Since several people have asked me about it I thought I'd post what I'd found out from some limited personal testing and talking with people at X-Rite (thanks).

How it works... ;-)

The first 50 patches are always the same set of device recipes (RGB or CMYK values).

With measurements from the first 50 patches, ColorMunki builds a profile and then runs a known set of Lab values (containing neutrals, skin tones, etc.) through the profile to determine roughly the device values of those desired colours.

This data is used to build the second target (which explains why the 2nd targets look quite similar)

Next, print and measure the newly created second target and then build the final profile using both sets of device recipe and measurement data.

This refinement process helps identify exactly where these key colour areas reside in the printer gamut.

In previous methods, it wasn't known which combination of device recipes actually printed neutral tones so more combinations of colours were printed/measured to find out.

The new iterative discovery process helps find these neutrals much more easily with fewer colour patches.

This is the key to the low patch count profiles but does depend on predictable behaviour of the printer in regions not sampled in the first set of patches.  This predictability is both a strength and potential weakness in the ColorMunki technique - I guess we'll have to wait for more people to do detailed testing, however you can bet that the algorithms have been tested on a lot of real world printers.

The image based optimisation works the same way as the second set of 50 patches.

The CM software automatically extract colours from the image, converts them to Lab (using the source / image profile)

The new target is then printed and measured. This information is then added to the previous measurement data set, and used to build a new profile.

Using this method, more information is gained about the printer's behaviour in the colour regions that were extracted from the refinement image.

The idea is that, next time you print an image using the new profile, the results will be even more colour accurate.

Because the process uses colours extracted from the image in this process, you can improve any colour region you want by using an image that contains those colours.

Since the process just adds additional pairs of device recipes and corresponding measured Lab values into the profile data set, it is a non-destructive process and can be repeated as many times as needed without damaging the profile.

Note that like with any profile building, this is subject to accurate measurements.
Remember as with many things 'Garbage in - garbage out'. This is one reason I'd want to give refined profiles a new name, since a duff set of measurements (one blocked nozzle for example) will mess up your profile and there is no easy way to undo things.

One area I'm curious to look at, is to see how well the CM profiles handle greyscale images, although it should be noted that there are no profile refinement options (such as true greys or paper relative greys) so it is a case of you get what you get. As ever, take this in context of the target market of the device - if you know of the difference about the greys, then you are in the ColorMunki 'Super Expert' category ;-)
[a href=\"index.php?act=findpost&pid=192269\"][{POST_SNAPBACK}][/a]
Logged

keith_cooper

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 473
    • Northlight Images
ColorMunki Profile refinement
« Reply #2 on: April 28, 2008, 10:35:18 am »

Hi

I'm hopeful that I'll be able to resume testing at the weekend ;-)

If you look at how the CM does its profiling then I'd suspect that if issues arise then they will be more likely with 3rd party inks.

The guestimates going into the low patch count targets are making some pretty broad assumptions about the results of the driver/ink/paper combination.

Whilst I was able to get a good profile using 3rd party inks on non OEM paper with an 1160, that was for colour.

Getting good greyscale with 3rd party inks is likely to need a more complex profiling solution than the ColorMunki. I tried the Printfix Pro (Spyder3print) on a 2400 with a CIS some time ago and got some really smooth greyscale images, but that was with the biggest set of patches and the greyscale ones too.

2400 article
Logged
bye for now -- Keith
[url=http://www.nor

Scho

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 95
    • http://photos.schophoto.com/
ColorMunki Profile refinement
« Reply #3 on: April 28, 2008, 05:54:26 pm »

I find it hard to believe that "3rd party inks" have anything to do with the grayscale profiling issue.  Do you really know that the software is using Lab LUTs for OEM inks?  Epson would love that I'm sure, but it doesn't seem a very realistic or appropriate way to build profiles.  Good grayscales are more a matter of how blacks are generated and which color inks are used for the composite grays, irrespective of the "brand" of ink.

I'm hopeful that I'll be able to resume testing at the weekend ;-)

If you look at how the CM does its profiling then I'd suspect that if issues arise then they will be more likely with 3rd party inks.

The guestimates going into the low patch count targets are making some pretty broad assumptions about the results of the driver/ink/paper combination.

Whilst I was able to get a good profile using 3rd party inks on non OEM paper with an 1160, that was for colour.

Getting good greyscale with 3rd party inks is likely to need a more complex profiling solution than the ColorMunki. I tried the Printfix Pro (Spyder3print) on a 2400 with a CIS some time ago and got some really smooth greyscale images, but that was with the biggest set of patches and the greyscale ones too.

2400 article
[a href=\"index.php?act=findpost&pid=192300\"][{POST_SNAPBACK}][/a]
[/quote]
Logged

keith_cooper

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 473
    • Northlight Images
ColorMunki Profile refinement
« Reply #4 on: April 28, 2008, 06:41:18 pm »

>I  find it hard to believe that "3rd party inks" have anything to do with the grayscale profiling

OEM Drivers are fine tuned for the particular characteristics of OEM  inks and their interaction with OEM papers.

Whilst 3rd party inks can be close and can give good results for colour prints, the slight differences sometimes show up more in neutrals. I've seen this when profiling printers using non OEM inks - not always, but it's a factor I'm wary of and might decide to use higher patch count targets because of it.

If you take an ink set that's far from the OEM then the low patch count approach is more likely to run into trouble, since it relies on some of the predictable behaviour that an OEM driver gives with OEM inks/paper

> Do you really know that the software is using Lab LUTs for OEM inks?

No, that's not it at all - there is no special treatment for OEM inks, it's just the OEM drivers are fine tuned for OEM inks/papers. The choice of patch colours assumes this 'tuning' to some extent. I'm not saying, by any means, that 3rd party inks won't work. I've tried them and got good results.

> Good grayscales are more a matter of how blacks are generated and which color inks are used for the composite grays, irrespective of the "brand" of ink.

Black generation and good neutrals depends on how inks and paper interact via what the driver does. Brand of ink most definitely does matter depending on just how close the characteristics of the ink match the OEM ink.  Results may be very close to what you're getting with OEM inks or they may be noticeably different.

I do agree that other solutions may lead to better B/W performance - that's why I tried using the ColorMunki to create ABW linearisation (QTR) icc profiles. The fact that you don't have any choice in grey generation in the ColorMunki might make B/W somewhat problematic with very warm or cool papers (I've no idea how the ColorMunki handles OBAs since it's a UV Cut spectro)
Logged
bye for now -- Keith
[url=http://www.nor
Pages: [1]   Go Up