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Lighten to specific K value?


tmg

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Hi All,
I have a b&w image that I need to lighten uniformly so that the darkest parts of the images are 65%K. Is there a precise way of doing this instead of using brightness sliders or curves?

Apologies if this should be in the newbies forum -- wasn't sure where to put it, so opted for general :)
Thanks! T
 

Tom Mann

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I am a bit confused by the terminology in your question.

When one mentions the "k" value of an image, one is almost always talking about a CMYK image, not a grayscale image (in which the brightness is reported in Photoshop as if it was an RGB value with all three values equal), and certainly not a 1 bit "b&w" image (which has no gray tones).

To make matters more confusing, different CMYK profiles obtain a specified gray color by different combinations of the color inks and the black ink, eg, a maximum black production scenario (ie, maximum k) will have a very different combination of inks than a standard SWOP profile.

So, can you please elaborate on the context for your question and your workflow.

Thanks,

Tom M
 

Tom Mann

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PS - In addition to general information on the workflow for this project, I specifically want to know how it will be printed, eg, with an inkjet or on an offset press.
 
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Open your Greyscale image.
Open the curves tool.

Bildschirmfoto 2016-03-24 um 20.31.46.png
1. Push the curve to 65%.
2. Click this icon. Choose SAVE. Give a name (Black and White 65%).
3.This saves your curve to the desktop. (You can choose any other place).

Open your next image.
Open the curves tool.
Click the icon 2. Choose LOAD.
This opens a submenu. Double-click on the name of your the saved curve. (Black and White 65% acv.).
The values change to 65%. Save your image.

This is a fast way if you have to adjust 20 or more images to the same values.
 

tmg

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Thanks for your reply Tom, and apologies for the messy terminology.

The image is in "Greyscale" mode. When I say K I mean black. I am using "K" because when I check the different black values in the image by running the Eyedropper tool over it, the number values in the info window are offered in percentage of K (there are no CMY values offered, not even 0%, just K).

Essentially I would like to lighten the entire image uniformly so that what are now K = 100% areas of the image, become K=65%.

Its essentially just lightening the whole image and I can do this crudely with the curve mask, but I was wondering if there is a way of doing it more precisely.

Thanks so much!
Tanja




I am a bit confused by the terminology in your question.

When one mentions the "k" value of an image, one is almost always talking about a CMYK image, not a grayscale image (in which the brightness is reported in Photoshop as if it was an RGB value with all three values equal), and certainly not a 1 bit "b&w" image (which has no gray tones).

To make matters more confusing, different CMYK profiles obtain a specified gray color by different combinations of the color inks and the black ink, eg, a maximum black production scenario (ie, maximum k) will have a very different combination of inks than a standard SWOP profile.

So, can you please elaborate on the context for your question and your workflow.

Thanks,

Tom M
 

Tom Mann

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That's fine, Chris, but if he is going to print his grayscale image on an ordinary, multicolor inkjet or 4 color offset press, the k-value seen in the curves dialog box won't even be close to the actual k value sent to the printer. That's why I was asking all the questions.

Tom M
 
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Tom Mann

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In addition, simply lifting the blacks isn't likely to produce the most visually pleasing result on any given printer. IMHO, to get the best look, he will likely have to modify the curve, as well.

I also wonder why his printer doesn't supply him with a profile for that particular machine which would avoid excess ink AND give the best output it is capable of on an image that looks perfect in the OP's monitor. This is the whole point of a fully color managed workflow, icc profiles, etc.
 

tmg

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Ah, yes -- well thats kind of the problem I am having. Its a little complicated -- apologies in advance...

I am getting the image printed on an inkjet printer on a transparency, for use as a sun print/cyanotype negative. It is being printed by a screenprinter which has a printer that has all 4 CMYK cartridges filled with black to get a more solid color. This means the prints are WAY darker printed than one would expect based on the original digital file. After getting a test strip printed with them, I have determined that 65% K, or black (as defined by photoshop in my Greyscale image) is the equivalent of pitch black in the print out I am getting from them. Unless I correct for this in the file I lose all detail between 65-100% K.

Does that make sense?
 

tmg

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Thanks -- I guess what I was looking for is the ausgabe/output value on the curve mask which I didn't actually notice was there! Thanks!
 

tmg

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Hi Tom, I guess my larger scale problem is that I haven't been able to get the printer to give me their printer info/settings, so I have to adjust my file based on the test print they gave me and hope their settings don't change. Its not ideal, but its what I'm working with. I have found very few people/printers that can print the kind of black density I need to fully block out the light when I am making the cyanotype prints. Thanks, T
 

MrToM

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I would also use a 'Curves' adjustment but instead of using the 0-255 scale, I'd use the Pigment / % scale.....its 0-100%.

You'll have to keep the slope at the same gradient for a uniform adjustment so change both points...

First black to 65%...

black_to_65_MT_01.png



...then to keep it uniform...

black_uniform_MT_01.png


Regards.
MrToM.
 

Tom Mann

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Ahh ... I was sure there was more to the story, LOL. You explained it perfectly! Thanks!

One thought: Just in case you weren't aware of this, there are commercial services that will profile any printer for you fairly inexpensively. They have u print out their test chart, they measure it on their spectrophotometer, and send you back an icc profile for that printer. Presumably they can do this even if all the inks have been switched to black (.. but check). This may help you in future projects.

The best of luck.

Tom M
 

Tom Mann

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...You'll have to keep the slope at the same gradient for a uniform adjustment so change both points...
I doubt that maintaining the same slope would produce a visually good image. For example, in addition to the requested change in the black point, maintaining the slope would also change the white point to a dull gray, and it's doubtful that the OP would want this given what he said.

Tom M
 

MrToM

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...I doubt that maintaining the same slope would produce a visually good image...
Possibly not.


...maintaining the slope would also change the white point to a dull gray...
Well my curves adjustment must be broken then because you can clearly see from my screenshots that all the input values have been lowered, and by the same amount...which is, as I understood it, what the OP requested...

...I need to lighten uniformly so that the darkest parts of the images are 65%K...

Regards.
MrToM.
 

Tom Mann

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Unfortunately, the OP (by his own admission) was not being precise in his terminology in that first post on which you based your method.

From what he said in subsequent posts, I firmly believe that he only wants a work-around for the "premature" onset of solid black, with a smooth transition to pure white in his unusual method of printing in which his printer uses 4 black ink cartridges instead of only one. His subsequent comments indicate that he is doing everything in his power to achieve maximum dynamic range, and greying the whites would do exactly the opposite: wildly reduce the dynamic range of his prints.

Perhaps the OP, tmg, will rejoin the discussion and let us know for sure which he prefers.

Cheers,

Tom M
 
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These are the results using two different methods.
Let the OP decide if this will help.

RobunnyB+W.jpg
Original

RobunnyB+W Chrisdesign.jpg
chrisdesign

RobunnyB+W MrTom.jpg
MrTom
 
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