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Author Topic: Sundry observations and questions  (Read 515 times)

BobDavid

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Sundry observations and questions
« on: May 12, 2018, 02:32:13 PM »

Thank you Doug Gray for explaining:

"...But to summarize why AbsCol compared to RelCol is rarely used in printing photos it's these two factors:

1. Clipping when L* exceeds the paper white.

2. Neutral colors are printed neutral and not shifted to the paper's actual white point. This creates pretty awful effects on prints with a white point that is more than 1 or 2 dE tint (a* and b* only). But it's only awful when the print has a white border. Borderless prints are printed more consistently with AbsCol as the printer takes out any tint the paper has. However, a significant tint reduces the printable gamut further beyond the effect in #1."


About six months ago, after purchasing an Epson SureColor P800 Inkjet Printer, I chose Epson Ultra Premium Photo Papers (Luster and glossy) as the go options for PK printing. I've always liked those papers except for the blueish tint from OBAs.

I observed that printing in AbsCol neutralizes the blue tint of the Epson media. Neutralizing the white point has improved the look of my nighttime scenes and other scenes where the edges of the picture are "dark." The phenomenon you pointed out about white borders appearing discolored relative to the picture is on the mark. Tangentially, if AbsCol neutralizes without clipping when L* exceeds the paper white, is the likelihood of clipping something that can be predetermine by referring to lab values displayed in the info window?

Another topic:

I sometimes convert an aRGB file to LAB. It's especially convenient for restoring faded/discolored/poorly exposed/dye-shifted color photographs from the 1950s up to the recent past (particularly pictures faded by the sun/UV). An adjustment or two in *a and *b often times works wonders. As an aside,  I occasionally apply sharpening to the L channel.

After making the corrections in LAB, I always convert back to aRGB, with the assumption it's okay to do so within reason.

I discovered this technique by reading Photoshop LAB Color by Dan Margulis. It helps with old photos and on rare occasion, pictures of landscapes overwhelmed by a dominant tint (e.g. a scene taken on a misty overcast day).

One of my pet peeves is the lack of precision in adjusting *a and *b along the curve as displayed in the graph. I attribute that to the X,Y graph being too small (low-res) to be able to precisely set mark points to define a spline curve. Am I missing something here?
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Mark D Segal

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Re: Sundry observations and questions
« Reply #1 on: May 12, 2018, 02:59:50 PM »

I don't know whether you've addressed this only to Doug or are opening it to general conversation, so assuming the latter, I'll jump in with a couple of points.

There is a 3rd factor differentiating AbsCol from RelCol with BPC: it applies most obviously when printing with matte papers for which Maximum Black is usually in the range of L*14 to L*18. If you use AbsCol all the Blacks below Maximum Black are squished to that level. If you use RelCol with BPC, there is a remapping of Black in the photo file to Black deliverable from the printer/paper combination and this tends to provide more differentiated Black shading appearance.

I'm assuming in your discussion of printing old photographs, you mean you are printing scans of the old photographs. If so, that would seem to suggest that however they are being scanned, they are not being colour corrected in the scanner software, but just digitized "as is". You can do it that way, but you'd make your imaging life easier by doing elementary restoration of faded photos and colour rebalancing in the scan software. SilverFast, for example, has user-friendly tools designed to do exactly this and they usually work well. Then you bring a more correct digital photo into your hard drive and you need not bother about Lab conversions for doing subsequent refinements in other image editing software. Nor do you need a Lab Luminance layer for satisfactory sharpening.
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Mark D Segal (formerly MarkDS)
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BobDavid

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Re: Sundry observations and questions
« Reply #2 on: May 12, 2018, 03:05:45 PM »

I don't know whether you've addressed this only to Doug or are opening it to general conversation, so assuming the latter, I'll jump in with a couple of points.

There is a 3rd factor differentiating AbsCol from RelCol with BPC: it applies most obviously when printing with matte papers for which Maximum Black is usually in the range of L*14 to L*18. If you use AbsCol all the Blacks below Maximum Black are squished to that level. If you use RelCol with BPC, there is a remapping of Black in the photo file to Black deliverable from the printer/paper combination and this tends to provide more differentiated Black shading appearance.

I'm assuming in your discussion of printing old photographs, you mean you are printing scans of the old photographs. If so, that would seem to suggest that however they are being scanned, they are not being colour corrected in the scanner software, but just digitized "as is". You can do it that way, but you'd make your imaging life easier by doing elementary restoration of faded photos and colour rebalancing in the scan software. SilverFast, for example, has user-friendly tools designed to do exactly this and they usually work well. Then you bring a more correct digital photo into your hard drive and you need not bother about Lab conversions for doing subsequent refinements in other image editing software. Nor do you need a Lab Luminance layer for satisfactory sharpening.

It's open to all. ... I especially wanted to thank Doug for explaining something that I didn't know I didn't know.
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BobDavid

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Re: Sundry observations and questions
« Reply #3 on: May 12, 2018, 03:17:14 PM »

Thanks Mark.

"There is a 3rd factor differentiating AbsCol from RelCol with BPC: it applies most obviously when printing with matte papers for which Maximum Black is usually in the range of L*14 to L*18. If you use AbsCol all the Blacks below Maximum Black are squished to that level. If you use RelCol with BPC, there is a remapping of Black in the photo file to Black deliverable from the printer/paper combination and this tends to provide more differentiated Black shading appearance."

Soft proofing proved early on to me that AbsCol is worthless for printing on matte paper. It's gratifying to learn a lesson quickly/easily/painlessly.

At the risk of opening up a can of worms, the way I've been able to get decent results on matte paper (assuming the file started out as aRGB) is to narrow the gamut by converting to sRGB. From there, convert the profile to CMYK, and then back again to sRGB.

This may sound wacky, but it's proven to work best for me, at least up to this point. I learned that trick from a commercial photographer who gets outstanding results that way. It's also helpful for him because he has to ensure a file will be compatible with SWOP.
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Mark D Segal

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Re: Sundry observations and questions
« Reply #4 on: May 12, 2018, 03:28:38 PM »

Thanks Mark.

.............

At the risk of opening up a can of worms, the way I've been able to get decent results on matte paper (assuming the file started out as aRGB) is to narrow the gamut by converting to sRGB. From there, convert the profile to CMYK, and then back again to sRGB.

This may sound wacky, but it's proven to work best for me, at least up to this point. I learned that trick from a commercial photographer who gets outstanding results that way. It's also helpful for him because he has to ensure a file will be compatible with SWOP.

Bob - if it works for you and you are happy with it it's not *necessarily* wacky. But what happens if you start with an image file that has wider gamut than sRGB? What you are doing with this process is using profile conversions to compress or change gamuts in a rather rote manner without you having any control over what's going on. The controlled way of compressing data from a wider space to a narrower space would be to keep the master photo in as wide a space as it originated, and use softproofing with the press or printer/paper profile to adjust the image so that it appears satisfactory to you under softproof in the printing conditions. This gives you free choice of all your editing tools and perhaps a more satisfying result.
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Mark D Segal (formerly MarkDS)
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Tim Lookingbill

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Re: Sundry observations and questions
« Reply #5 on: May 12, 2018, 03:33:06 PM »

Soft proofing proved early on to me that AbsCol is worthless for printing on matte paper. It's gratifying to learn a lesson quickly/easily/painlessly.

At the risk of opening up a can of worms, the way I've been able to get decent results on matte paper (assuming the file started out as aRGB) is to narrow the gamut by converting to sRGB. From there, convert the profile to CMYK, and then back again to sRGB.

This may sound wacky, but it's proven to work best for me, at least up to this point. I learned that trick from a commercial photographer who gets outstanding results that way. It's also helpful for him because he has to ensure a file will be compatible with SWOP.

I've used similar conversion hacks to change the gradation scaling to black point on some images giving me trouble in this area but never considered doing it for printing. Makes sense to me.

One question, are you using AbsCol during the conversion to CMYK and back to sRGB? Or is it all straight RelCol?

And a suggestion, ICC website came up with special sRGB variant that does something similar to shadow gradients so you might experiment with that approach.

No can of worms for me. If it works, use it.
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BobDavid

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Re: Sundry observations and questions
« Reply #6 on: May 12, 2018, 03:37:48 PM »

Bob - if it works for you and you are happy with it it's not *necessarily* wacky. But what happens if you start with an image file that has wider gamut than sRGB? What you are doing with this process is using profile conversions to compress or change gamuts in a rather rote manner without you having any control over what's going on. The controlled way of compressing data from a wider space to a narrower space would be to keep the master photo in as wide a space as it originated, and use softproofing with the press or printer/paper profile to adjust the image so that it appears satisfactory to you under softproof in the printing conditions. This gives you free choice of all your editing tools and perhaps a more satisfying result.

I cannot dispute that. But the gamut of a hot press paper without OBAs has a narrow gamut to begin with. Is that sound logic?
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Mark D Segal

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Re: Sundry observations and questions
« Reply #7 on: May 12, 2018, 03:41:34 PM »

Yes, it's true that the gamut of hot press matte paper is much less than that of quality luster/gloss paper and also probably much less than that of many image files. This is all the more reason to use soft-proofing with the full range of editing tools at your disposition rather than relying on a robotic process. No doubt the latter is much faster, relatively painless, but is it optimal? I would think only by happenstance. Much depends on whether you are aiming for speed or optimization.
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Mark D Segal (formerly MarkDS)
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BobDavid

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Re: Sundry observations and questions
« Reply #8 on: May 12, 2018, 04:01:45 PM »

"...nor do you need a Lab Luminance layer for satisfactory sharpening.

I agree it’s not necessary to sharpen in L. It’s helpful for checking micro contrast, especially with scenes where a subject has muted color and the sky is hazy/misty/overcast. It’s just a trick up the sleeve that comes in handy. Generally, I stay away from sharpening altogether except for increasing micro contrast or for enhancing a particular area of an image. Careful camera technique combined with  good lenses is the best way to achieve a crisp image.
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Doug Gray

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Re: Sundry observations and questions
« Reply #9 on: May 12, 2018, 04:06:56 PM »

There is a 3rd factor differentiating AbsCol from RelCol with BPC: it applies most obviously when printing with matte papers for which Maximum Black is usually in the range of L*14 to L*18. If you use AbsCol all the Blacks below Maximum Black are squished to that level. If you use RelCol with BPC, there is a remapping of Black in the photo file to Black deliverable from the printer/paper combination and this tends to provide more differentiated Black shading appearance.
Yep. You will note that when I refer to RelCol it is w/o BPC unless otherwise stated. AbsCol and RelCol suffer the same problems at the black point and it is much worse with matte prints. There is an additional problem that often shows up, abrupt changes in hue. As one goes out of gamut on the dark side :) profiles map to the closest part of the printable gamut and that is usually the darkest black but one with a different hue than the printable, in gamut black which tracks the chromaticity of the paper's white for RelCol, or neutrals for AbsCol.

That said, I find making replicas of things like old newspaper clippings is quite effective with matte papers and AbsCol. Newsprint almost never has blacks below matte blacks so these problems don't appear. Using BPC in these instances will materially lighten the printed blacks by raising the L* unnecessarily. On occasion, where the blacks in an image I'm trying to replicate using matte are not too far below the printable gamut, I'll make an ad hoc "BPC" by a curves layer. Dragging the black point in curves up just enough to get the image inside the printable gamut eliminates the hue shift and blocking that would otherwise occur without the larger luminance increase just using RelCol with BPC introduces. And, of course, BPC isn't available in AbsCol.

These things are areas of advantage in Photoshop since Lightroom only offers RelCol and Perc. and always turns on BPC. OTOH, Lightroom doesn't expose users to these, often unanticipated and not understood, aspects of printing limitations.
« Last Edit: May 12, 2018, 04:15:42 PM by Doug Gray »
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BobDavid

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Re: Sundry observations and questions
« Reply #10 on: May 12, 2018, 04:10:04 PM »

"Yes, it's true that the gamut of hot press matte paper is much less than that of quality luster/gloss paper and also probably much less than that of many image files. This is all the more reason to use soft-proofing with the full range of editing tools at your disposition rather than relying on a robotic process. No doubt the latter is much faster, relatively painless, but is it optimal? I would think only by happenstance. Much depends on whether you are aiming for speed or optimization."

This is just a general rule that comes in handy. And it works especially well when shooting in the studio where it's possible to control color, contrast ratios, etc. True, the output has a narrower gamut. But it's easier to get an image to "pop." I hardly ever print on hot press or other matte papers unless the subject calls out for it. I like hot press for reproducing documents, etchings, and pastels. 
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Mark D Segal

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Re: Sundry observations and questions
« Reply #11 on: May 12, 2018, 04:16:48 PM »

.................

These things are areas of advantage in Photoshop since Lightroom only offers RelCol and Perc. and always turns on BPC. OTOH, Lightroom doesn't expose users to these, often unanticipated and not understood, aspects of printing limitations.

That's because the design philosophy underpinning this application from the get-go was to keep it easy and provide for the needs of most photographers most of the time, knowing that for more arcane stuff there is always the 800 Lb gorilla waiting in the wings with a simple "Edit In....." command.  :-)
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Mark D Segal (formerly MarkDS)
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BobDavid

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Re: Sundry observations and questions
« Reply #12 on: May 12, 2018, 05:03:19 PM »

"I'm assuming in your discussion of printing old photographs, you mean you are printing scans of the old photographs. If so, that would seem to suggest that however they are being scanned, they are not being colour corrected in the scanner software, but just digitized "as is". You can do it that way, but you'd make your imaging life easier by doing elementary restoration of faded photos and colour rebalancing in the scan software. SilverFast, for example, has user-friendly tools designed to do exactly this and they usually work well. Then you bring a more correct digital photo into your hard drive and you need not bother about Lab conversions for doing subsequent refinements in other image editing software. Nor do you need a Lab Luminance layer for satisfactory sharpening."

I rarely use a scanner, except for the sake of expediency or for noncritical work.

Years ago, I customized an industrial copy stand for reproducing art and resuscitating antique photographs and documents. I shot with a 39MP multi-shot Hasselblad back fitted onto a custom pancake camera that accepted Schneider Digitars with electronic shutters.

I got rid of the Hassey/Schneider stuff years before I closed my business. … Believe it or not my $999 Pen-F in 8-shot mode is almost as good and in some ways better than the Hasselblad. The inconvenience with multi-shot is it takes a minute to cycle through one capture, and I don’t like beating  up my Elinchrom strobes. So for lesser demanding work, the Sony A7r II is fine.

The stand is located in a neutral grey space, the ceiling is covered with black velvet. I generally use two Elinchrom monoblocks locked down on C-stands. 12” X 12” polarizing gels backed with heat absorption Rosco filters clamp onto “magic arms” and polarizer filters are at hand for inserting on the lens for cross polarization. Whether or not to cross polarize depends on the application. 
 
My backlight setup is pretty slick. I used to use an Elinchrom Quadra / diffusion box setup. I’ve replaced it with a continuous current LED circular light. Color temp and wattage are adjustable, the illumination is virtually even across a 7” X 7” field. The CRI is > 96, R8-9. I mostly use the Sony for backlit work.
« Last Edit: May 12, 2018, 05:37:33 PM by BobDavid »
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