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Author Topic: b&w print color cast  (Read 7273 times)
meakai
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« on: December 31, 2006, 11:19:56 PM »
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I sometimes get a sepia or magenta cast in my b&w prints.

I use a hp 8750 printer and hahnemuhle rag paper and a custom icc. I adjusted my temperature in Bridge on one of the photos and it got rid of the cast, but it was all a guess and it didn't work on subsequent photos.

Is this a white balance problem before conversion? What can I do to get consistent neutural tones?
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Brian Gilkes
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« Reply #1 on: January 01, 2007, 04:16:35 AM »
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I'm not familiar with that printer, but you should not be getting a cast. Using current inksets and profiles your prints on HPR should be absolutely neutral, with all tones seperating, when printing with all colours. This is my current experience. Perhaps you should post your workflow. You may have slipped up somewhere. We hava all done that.
Main points to check:
File should be in a colour space. For B&W a small space like sRGB is fine.
Ensure source space is as above, and destination is the profile
Ensure driver is the one for which the profile was made
There should be no colour adjustment in the printer driver.
HTH
Brian
www.pharoseditions.com.au
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meakai
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« Reply #2 on: January 01, 2007, 12:30:57 PM »
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Thanks Brian. I have since read an article in Luminous Landscape on RIP that helps to clarify where some of the problem may stems from. Again, your comments were very much appreciated.
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colourperfect
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« Reply #3 on: January 01, 2007, 12:58:33 PM »
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Do a desaturate on an image to ensure you have got true B+W.
Make sure you are back in RGB, go for sRGB or AdobeRGB
Then regardless of the WB settings you will have just B+W and grey's in between.

Ian

http://profiles.colourperfect.co.uk


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I sometimes get a sepia or magenta cast in my b&w prints.

I use a hp 8750 printer and hahnemuhle rag paper and a custom icc. I adjusted my temperature in Bridge on one of the photos and it got rid of the cast, but it was all a guess and it didn't work on subsequent photos.

Is this a white balance problem before conversion? What can I do to get consistent neutural tones?
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meakai
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« Reply #4 on: January 01, 2007, 09:03:19 PM »
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Thanks Ian. I've been reading up more on the subject and now believe it has to do with how much cyan and magenta is in the image. RIPs like Image Print avoid using those two colors when printing b&w to avoid the cast it may cause. That sort of makes sense to me because some of my photos are totally neutural while others have a cast. Even though it may show up as totally neutural on the screen, the printer is unable to print a pure neutural print because of the amount of cyan and magenta in the photo. So, no matter what steps you take to convert to b&w, you're still printing in RGB to make your grey and black tones.

Thank you very much for your help on this matter.

Bill
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Jonathan Wienke
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« Reply #5 on: January 02, 2007, 02:54:34 AM »
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I sometimes get a sepia or magenta cast in my b&w prints.

I use a hp 8750 printer and hahnemuhle rag paper and a custom icc. I adjusted my temperature in Bridge on one of the photos and it got rid of the cast, but it was all a guess and it didn't work on subsequent photos.

Is this a white balance problem before conversion? What can I do to get consistent neutural tones?

If you're printing B&W images, why are you still in RGB mode? You're unnecessarily tripling your file size, as well as setting yourself up for failure. If you want to print B&W, convert to B&W mode, working space of gray gamma 1.8 or gray gamma 2.2. After you've done that, if you're still having problems, you are using incorrect color management settings or else have a bad profile. Post your print dialog settings, as well as your photoshop color management settings.
« Last Edit: January 02, 2007, 02:54:58 AM by Jonathan Wienke » Logged

colourperfect
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« Reply #6 on: January 02, 2007, 10:33:01 AM »
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Johnathan,

Many images that people call B+W are actually monochrome with a slight warm or cool tint to them. I prefer a workflow that doesn't change the moment you go away from pure neutrality.

Incidently won't the printer and profiles most normal people work with assume you are sending an RGB file with RGB source space ?

Accepted some fire CMYK files at printers but this isnt recommended for most printers.

Ian

http://www.colourperfect.co.uk


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If you're printing B&W images, why are you still in RGB mode? You're unnecessarily tripling your file size, as well as setting yourself up for failure. If you want to print B&W, convert to B&W mode, working space of gray gamma 1.8 or gray gamma 2.2. After you've done that, if you're still having problems, you are using incorrect color management settings or else have a bad profile. Post your print dialog settings, as well as your photoshop color management settings.
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meakai
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« Reply #7 on: January 02, 2007, 01:52:14 PM »
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[/quote]

Jonathan,

Right or wrong, I follow the school of thought that you'll fet more shades of grey (gamet if you will) with RGB than with just the 256 shades by using just black ink. However, I appreciate your input and I will look into your suggestion none the less.

Thanks,

Bill
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Jonathan Wienke
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« Reply #8 on: January 04, 2007, 01:41:49 PM »
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Jonathan,

Right or wrong, I follow the school of thought that you'll fet more shades of grey (gamet if you will) with RGB than with just the 256 shades by using just black ink. However, I appreciate your input and I will look into your suggestion none the less.

That's definitely wrong, because to get neutral colors in RGB mode, you must lock the RGB channel values together so that red=green=blue, which means that you still have only 256 tonal gradations even when in RGB mode. If you deviate from red=green=blue, then you are by definition introducing a color cast, which is the problem you are trying to avoid. If you need finer tonal gradations, edit in 16-bit mode, which gives you over 32,000 tonal steps between black and white; more than any display and most printers are capable of reproducing, and definitely finer steps than the eye can distinguish.

If you're referring to using all the inks in the printer instead of only the black/grays, that has nothing to do with whether your image file is RGB or grayscale. Unless you force black/gray ink use only in the printer driver settings, small amounts of colored inks are used to cancel out color casts even when printing grayscale-only images. This is generally preferable, as printing with black/gray ink only will still result in a color cast due to the interaction of the ink with the paper and other factors. The printer profile is what determines how much of the colored inks are used to achieve true neutrality. If you are printing a grayscale-only image and are not getting neutral tones from black to white, then you have a bad profile or some of your printer driver settings are incorrect.
« Last Edit: January 04, 2007, 01:53:38 PM by Jonathan Wienke » Logged

Gary Brook
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« Reply #9 on: January 04, 2007, 02:48:27 PM »
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The 8750 gives you the option of printing with black and gray inks only by selecting, I think, 'grayscale' in the printer driver.  So, unless you want a deliberate tint, or a coloured feature in an otherwise b&w image, selecting this will dispense with any colour casts you might be experiencing.  That said, my experience with a custom rgb profile on a similar model, the HP 7960, was that the driver and profile were substantially linear/neutral and gave lovely b&w prints.  One last suggestion, starting with an image in aRGB colour space makes the profile work harder and can introduce larger conversion errors that show up as small colour casts.  I have found that you can get a more neutral b&w by first converting a copy of your image to a smaller RGB space, such as sRGB, before printing.  Regards,

Gary.
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meakai
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« Reply #10 on: January 04, 2007, 10:33:01 PM »
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Quote from: Jonathan Wienke,Jan 4 2007, 12:41 PM

Jonathan,

Thanks again for your input, but I believe I threw everyone off track a little by the way I stated things.

I do get very neutural prints most of the time, but was puzzled as to why i would get a cast with certain images every once in a while. It appears to be image related since I can print a different image repeatedly without any problem. I was actually able to improve one image by adjusting the color temperature while in RAW, although I was not successful with another image. Thus, I started this thread to see if I was on the right track even if not completely successful yet.

Bill
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meakai
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« Reply #11 on: January 04, 2007, 10:39:07 PM »
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Gary,

Interesting. I've never heard of the sRGB thing before. I'll try it out of curiosity, if nothing else. Thanks!

Bill
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Jonathan Wienke
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« Reply #12 on: January 05, 2007, 01:50:53 AM »
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I do get very neutural prints most of the time, but was puzzled as to why i would get a cast with certain images every once in a while. It appears to be image related since I can print a different image repeatedly without any problem. I was actually able to improve one image by adjusting the color temperature while in RAW, although I was not successful with another image. Thus, I started this thread to see if I was on the right track even if not completely successful yet.

If you can alter the color cast of a print by changing the WB setting during RAW conversion, your B&W workflow is deeply flawed. If you're actually converting to B&W, the WB setting during RAW conversion will have no effect on color cast under any circumstances; the only thing it can affect is tonality. You are doing something dramatically wrong somewhere.

Gary, your suggestion is not very useful. If you are working with actual B&W images in any RGB editing space, the values of the red, green, and blue channels are always going to be equal, regardless whether your editing space is sRGB, AdobeRGB, or ProPhoto. Because of that, the choice of editing space is moot. If you are working with toned images, sRGB is the best choice for 8-bit images, but when in 16-bit mode, the level of color precision in larger-gamut spaces like ProPhoto is still greater than the precision of the printer.
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colourperfect
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« Reply #13 on: January 05, 2007, 03:27:54 AM »
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Gary may have a point if perceptual rendering was used. Then the rendering engine will shift all colours according to the ratio of the editing space to the output space. AdobeRGB being a larger space could introduce larger errors.

Incidently this is a theoretical possibility not one which I have tested to death.

For this reason I would recommend using rel col rendering if you think this is a problem. Rel Col clips any out of gamut colours (none in the case of B+W) and leaves all other colours alone.

We all need to also consider the effect of paper colour on B+W tones and whether the profile, if used, tries to compensate. Another source of errors is the profile not exactly compensating for OB's. I appreciate that the profiling s/w claims to compensate but I have seen some examples when it can't do this completely.

Ian

http://www.colourperfect.co.uk



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Gary, your suggestion is not very useful. If you are working with actual B&W images in any RGB editing space, the values of the red, green, and blue channels are always going to be equal, regardless whether your editing space is sRGB, AdobeRGB, or ProPhoto. Because of that, the choice of editing space is moot. If you are working with toned images, sRGB is the best choice for 8-bit images, but when in 16-bit mode, the level of color precision in larger-gamut spaces like ProPhoto is still greater than the precision of the printer.
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« Last Edit: January 05, 2007, 03:29:28 AM by colourperfect » Logged
Stephen Best
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« Reply #14 on: January 05, 2007, 03:43:12 AM »
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Gary may have a point if perceptual rendering was used. Then the rendering engine will shift all colours according to the ratio of the editing space to the output space. AdobeRGB being a larger space could introduce larger errors.
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This isn't how perceptual rendering works. The only way there could be a difference is if there were colours that were clipped on the transition to the smaller space. The size of the working space itself makes no difference to the rendering (relative colorimetric or perceptual). The colours get mapped, not the space. This has been discussed here a number of times.
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Jack Flesher
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« Reply #15 on: January 05, 2007, 11:23:26 AM »
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FWIW, I leave all my B&W images in my normal RGB working space and have NO issues with color shifts.  In this fashion, the original color information is always available should I want to tweak the net gray tonal value rendered from the base image colors; filter after the fact if you prefer.  This option is zapped once you convert to grayscale.

ALL I need to print good B&W is a good COLOR profile for my Epson K3 printers and they'll render grays as gray.  (I do *not* use Epson's advanced B&W driver as it does not provide the amount of control that working with a good profile does.)  Alternatively, you can get there with other printers using a RIP or a dedicated mono ink-set, or possibly by just specifying the K inks in the print driver if it allows for that.  

Cheers,
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colourperfect
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« Reply #16 on: January 05, 2007, 05:04:39 PM »
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Stephen,

Have a look here

http://www.cambridgeincolour.com/tutorials...-conversion.htm

For perceptual rendering to fit in transformed colours that were out of gamut it needs to move or 'shuffle' in gamut colours such that colours towards the edge of the gamut  dont merge together giving posterisation. As such if you use percetual rendering the risk of colour shifts is there. The shuffling algorithm is the 'secret' bit. With a huge space such as ProPhoto then the shifts are likely to be bigger as the out of gamut editing space when referred to the print space is huge.

A theoretical look initially suggests that colour casts would be moved towards neutrality. This however assumes that the neutrality axis is the axis towards which all shifts occur. I dont however believe this is the case.

At the end of the day if you use Rel Col you only shift colours if they are out of gamut. To my knowledge no B+W 'colours' are out of gamut of sRGB.

Therefore stick with sRGB and Rel Col rendering for a lower risk approach to B+W printing on most inkjet printers.

Ian

http://www.colourperfect.co.uk





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This isn't how perceptual rendering works. The only way there could be a difference is if there were colours that were clipped on the transition to the smaller space. The size of the working space itself makes no difference to the rendering (relative colorimetric or perceptual). The colours get mapped, not the space. This has been discussed here a number of times.
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Stephen Best
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« Reply #17 on: January 05, 2007, 05:39:10 PM »
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With a huge space such as ProPhoto then the shifts are likely to be bigger as the out of gamut editing space when referred to the print space is huge.
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At the risk of boring everyone, let's go over what happens when you map from your working space to the printer space. Each pixel in your working space has RGB coordinates which are mapped to absolute coordinates in the PCS via the working space profile. From there, they're then mapped to device dependent printer values using the perceptual tables in the printer profile. These perceptual tables, generated by the profiling software, are fixed. They also have to be able to handle any coordinates in the PCS. The CMM may build on-the-fly tables to streamline the process, but it's still a two-step translation. The second stage has no knowledge of the size/shape of the input working space, though it may make some assumptions about it. When you change from one working space to another (with Convert Profile) the colours stay the same (they will still map to the same coordinates in the PCS) but their RGB values will change. So whether the space is small or large makes no difference. The working space is merely the container for the image colours. A larger working space will have a higher gamut (possible image colours) but if the actual colours are the same, they'll render the same.

The problem here is the simplistic diagrams that show one gamut being massaged to fit into the other. It doesn't quite work like this. Don't worry, yours is a common misunderstanding.
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Jonathan Wienke
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« Reply #18 on: January 07, 2007, 07:59:09 AM »
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All of this debate is irrelevant to the OP's question. The gamut of any RGB working space is adequate for R=G=B monochrome images, so when converting, regardless of the rendering intent, no gamut compression is necessary to fit the source into the destination.
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Jack Flesher
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« Reply #19 on: January 07, 2007, 10:43:54 AM »
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All of this debate is irrelevant to the OP's question. The gamut of any RGB working space is adequate for R=G=B monochrome images, so when converting, regardless of the rendering intent, no gamut compression is necessary to fit the source into the destination.
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Agreed, but the rendering intent chosen can affect the overall gamma of the B&W image.
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