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Author Topic: lightening image in Photoshop  (Read 7823 times)
gkroeger
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« on: January 03, 2008, 05:27:25 PM »
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I have some images that have ideal color and good black and white points, but need some overall lightening for printing on the new Epson Exhibition Fiber paper.

The two ways I know of to do this are to use either a curves adjustment layer, and bow the curve upward slightly leaving the endpoints fixed... or, use a levels adjustment layer and shift the midpoint slightly.  I am trying to understand the difference between these two approaches.  Is the levels approach like using a linear distribution on either side of the midpoint?

Any better approach that won't mess with color or saturation?  I am assuming the brightness/contrast control moves endpoints?

Glenn
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Nat Coalson
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« Reply #1 on: January 03, 2008, 05:38:11 PM »
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You've got the right idea. If you just do a slight midpoint (gamma) move in Levels, it will look very much like a slight Curve adjustment. But the data is being manipulated differently.

Curves gives much more control than Levels. With curves, you can"pin" parts of the tone range that you don't want affected, and add more or less adjustment to different parts of the tone curve.

With either type of adjustment layer you can set the blending mode to Luminosity. This will only affect the overall "brightness" of the image and not affect color.

I'd suggest trying several methods to see what gives you the best results, then look at what's happening with the settings to better understand how each method affects the image.

And whenever possible make sure you're doing your editing in 16-bit.
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gkroeger
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« Reply #2 on: January 03, 2008, 06:04:56 PM »
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You've got the right idea. If you just do a slight midpoint (gamma) move in Levels, it will look very much like a slight Curve adjustment. But the data is being manipulated differently.

Curves gives much more control than Levels. With curves, you can"pin" parts of the tone range that you don't want affected, and add more or less adjustment to different parts of the tone curve.

With either type of adjustment layer you can set the blending mode to Luminosity. This will only affect the overall "brightness" of the image and not affect color.

I'd suggest trying several methods to see what gives you the best results, then look at what's happening with the settings to better understand how each method affects the image.

And whenever possible make sure you're doing your editing in 16-bit.
[a href=\"index.php?act=findpost&pid=164883\"][{POST_SNAPBACK}][/a]

Thanks Nat... by the way, it there a quick way to find the brightest and darkest pixels in an image and their RGB values?  I am used to having this feature in remote sensing software, but I don't see it in any of the histogram displays in PS.

Glenn
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rdonson
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« Reply #3 on: January 03, 2008, 06:41:06 PM »
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Thanks Nat... by the way, it there a quick way to find the brightest and darkest pixels in an image and their RGB values?  I am used to having this feature in remote sensing software, but I don't see it in any of the histogram displays in PS.

Glenn
[a href=\"index.php?act=findpost&pid=164890\"][{POST_SNAPBACK}][/a]

The simplest way may be to use the "Threshold" from the layers palette.  Move the slider all the way to the left until everything is white, then start moving to the right until black starts to appear.  Mouse over with the eyedropper and you should be able to read the RBG values in the "Info" window.  Repeat only from the right side to identify the brightest pixels.  

You can also use Command/Control - spacebar to temporarily activate the Zoom tool then click and drag to zoom in.

HTH
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[span style='font-size:14pt;line-height:100%'][span style='font-family:Arial'][span style='font-family:Geneva'][span style='font-size:8pt;line-height:100%']Regards,
Ron[/span][/span][/span][/span]
Jon Meddings
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« Reply #4 on: January 04, 2008, 09:29:13 AM »
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I have some images that have ideal color and good black and white points, but need some overall lightening for printing on the new Epson Exhibition Fiber paper.

The two ways I know of to do this are to use either a curves adjustment layer, and bow the curve upward slightly leaving the endpoints fixed... or, use a levels adjustment layer and shift the midpoint slightly.  I am trying to understand the difference between these two approaches.  Is the levels approach like using a linear distribution on either side of the midpoint?

Any better approach that won't mess with color or saturation?  I am assuming the brightness/contrast control moves endpoints?

Glenn
[a href=\"index.php?act=findpost&pid=164880\"][{POST_SNAPBACK}][/a]

Some great suggestions here already so I'll just throw out another technique I'll occassionly use to increase brightness/exposure.

- duplicate layer and then set blend mode to screen.

- using the opacity slider you can vary the overall effect and by using a mask on the layer you can limit the effect to specific regions/tones etc.
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Hunter
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« Reply #5 on: January 04, 2008, 12:15:07 PM »
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Thanks Nat... by the way, it there a quick way to find the brightest and darkest pixels in an image and their RGB values?  I am used to having this feature in remote sensing software, but I don't see it in any of the histogram displays in PS.

Glenn
[a href=\"index.php?act=findpost&pid=164890\"][{POST_SNAPBACK}][/a]

Glenn- just use the "Navigator" panel with the eye dropper tool or color sampler tool.
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Chris_T
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« Reply #6 on: January 05, 2008, 07:59:21 AM »
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As noted by others, there are many tools/methods for tonal corrections in PS. However, the simpler ways (i.e. without masking, blending multiple layers, etc.) may result in undesireable consequences. For example, using curves can easily lighten/darken an image. But this is achieved at the expense of altering the image's contrast. At the steepened part of the curve contrast is increased, while at the flattened part the contrast is reduced. Color and saturation can also be affected.

These side effects are seldom addressed in most books and tutorials. Here's an exception that goes to some length for each tool/method (starting in part II):

http://ronbigelow.com/articles/shadow/shad...-highlight1.htm
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01af
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« Reply #7 on: January 07, 2008, 07:04:01 AM »
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I have some images that have ideal color and good black and white points, but need some overall lightening for printing on the new Epson Exhibition Fiber paper.[a href=\"index.php?act=findpost&pid=164880\"][{POST_SNAPBACK}][/a]
Same problem here. With my Epson 3800 printer, most prints come out too dark (on any paper). The tones are all here, no murky shadows ... but still the overall impression is too dark.


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The two ways I know of to do this are to use either a curves adjustment layer, and bow the curve upward slightly leaving the endpoints fixed ... or, use a levels adjustment layer and shift the midpoint slightly.  I am trying to understand the difference between these two approaches.[a href=\"index.php?act=findpost&pid=164880\"][{POST_SNAPBACK}][/a]
There is none.


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If you just do a slight midpoint (gamma) move in Levels, it will look very much like a slight Curve adjustment. But the data is being manipulated differently.[a href=\"index.php?act=findpost&pid=164883\"][{POST_SNAPBACK}][/a]
No, it's not. As long as you're using just one additional point to manipulate the curve (and leave the endpoints alone), the effect will be exactly the same as moving the middle (gray) slider in Levels. The whole Levels dialog is just a different (simpler) user interface to the Curves functionality.


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Curves gives much more control than Levels.[a href=\"index.php?act=findpost&pid=164883\"][{POST_SNAPBACK}][/a]
More control, yes. Still there is nothing in Levels that you can't do in Curves also. In Curves, you can do anything that you can do in Levels, and then some.

Does this mean the Levels dialog is obsolete? No, it doesn't, because some kinds of manipulation are easier and/or quicker to do via Levels than through the more complex---and thus, more powerful---Curves interface.


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And whenever possible make sure you're doing your editing in 16-bit.[a href=\"index.php?act=findpost&pid=164883\"][{POST_SNAPBACK}][/a]
That's good advice---but it does not mean you're supposed to switch to 16-bit mode before editing 8-bit data. If the image already is in 8-bit format then you can leave it there; going into 16-bit mode from 8-bit is pointless. [EDIT: This is not generally correct---please read the following posts.]

But if it is in 16-bit mode, then by all means do your editing of tones, colours, and contrast first (profile conversions, too) and switch down to 8-bit mode later.


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Any better approach that won't mess with color or saturation?[a href=\"index.php?act=findpost&pid=164880\"][{POST_SNAPBACK}][/a]
I prefer to lighten up my images for print through the Screen blending mode. Either flatten your image or create a new top-most layer and merge all visible layers into it.  Then duplicate the top-most layer and set the blending mode to Screen. Reduce the opacity to somewhere between 5 % and 25 %; 15 % seems to be a good starting point for most cases. The Screen blending mode will lighten up the image in a very natural-looking way, and will affect shadows more than highlights.

You can achieve exactly the same result (including the opacity reduction) purely via Curves if you know how---but via the Screen blending mode it's far easier IMHO.

-- Olaf
« Last Edit: January 07, 2008, 08:43:20 AM by 01af » Logged
Jonathan Wienke
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« Reply #8 on: January 07, 2008, 07:51:56 AM »
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That's good advice---but it does not mean you're supposed to switch to 16-bit mode before editing 8-bit data. If the image already is in 8-bit format then you can leave it there; going into 16-bit mode from 8-bit is pointless.

You are incorrect. Even if the source image is only 8-bit, you're still better off stitching to 16-bit mode immediately. If you start out with 256 levels and edit in 8-bit, after only a few edits (curves, levels, etc) you'll have significantly fewer than 256 levels left due to quantization and rounding errors. But if you switch to 16-bit mode immediately, you'll still have 256 levels left even after extensive editing and adjustments. Switching to 16-bit mode won't give you more than 256 levels, but it will let you keep all of the ones you already have.
« Last Edit: January 07, 2008, 07:53:10 AM by Jonathan Wienke » Logged

01af
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« Reply #9 on: January 07, 2008, 08:36:37 AM »
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[...] it does not mean you're supposed to switch to 16-bit mode before editing 8-bit data. If the image already is in 8-bit format then you can leave it there; going into 16-bit mode from 8-bit is pointless.[a href=\"index.php?act=findpost&pid=165598\"][{POST_SNAPBACK}][/a]
You are incorrect. Even if the source image is only 8-bit, you're still better off switching to 16-bit mode immediately. If you start out with 256 levels and edit in 8-bit, after only a few edits (curves, levels, etc) you'll have significantly fewer than 256 levels left due to quantization and rounding errors. But if you switch to 16-bit mode immediately, you'll still have 256 levels left even after extensive editing and adjustments. Switching to 16-bit mode won't give you more than 256 levels, but it will let you keep all of the ones you already have.[a href=\"index.php?act=findpost&pid=165603\"][{POST_SNAPBACK}][/a]
Jonathan, you made me think about it ... and yes, I was incorrect. But so are you.

When applying only one step of adjustment then switching to 16-bit from 8-bit mode is pointless. Switching to 16-bit mode, applying the adjustment, and then switching back to 8-bit mode will yield exactly the same result as applying the same adjustment directly to the 8-bit data.

However when planning several steps of adjustments (i. e. more than one) then switching to 16-bit mode prior to the editing and then back to 8-bit after having done all steps will be beneficial. Doing several steps in 8-bit mode will accumulate the rounding errors of each step quickly; doing them in 16-bit mode will yield only the same loss as one step would in 8-bit mode.

But there will be a loss in any case that would not be there if the data was 16-bit from the beginning. Not all 256 levels will necessarily be preserved. Anyway, I stand corrected: Do switch to 16-bit mode before applying any major tone or colour shifts---because most likely, you will apply more than one editing steps. However, do not switch back to 8-bit mode between steps, or the whole benefit of switching will get lost.

So the ranking of methods is this:

Best: Acquire the image data as 16-bit and never switch to 8-bit mode until you're done with all your tone, colour, and contrast adjustments.

Not so good but better than nothing: Before applying any tone, colour, or contrast adjustments to 8-bit data, switch to 16-bit mode and don't return until you're done.

Worst: Do all your tone, colour, and contrast adjustments in 8-bit mode.

-- Olaf
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Jonathan Wienke
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« Reply #10 on: January 07, 2008, 09:57:00 AM »
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Jonathan, you made me think about it ... and yes, I was incorrect. But so are you.

When applying only one step of adjustment then switching to 16-bit from 8-bit mode is pointless. Switching to 16-bit mode, applying the adjustment, and then switching back to 8-bit mode will yield exactly the same result as applying the same adjustment directly to the 8-bit data.

True, but in practial terms, how many times would you do only one adjustment on an image? Typically you'll do noise reduction, a curve or level tweak or two, maybe some hue or saturation tweaks, and some sharpening, often more than one round at various radius and strength settings.
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Hank
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« Reply #11 on: January 07, 2008, 09:59:33 AM »
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On empirical side, I find it a lot easier to control color changes when using Selective Color rather than Curves.  Using the Black slider on each of the colors lets you adjust colors individually without affecting the others ala Curves.  It's especially useful for skies, but can be used effectively on the full spectrum.
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standard_observer
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« Reply #12 on: January 07, 2008, 04:20:37 PM »
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... using curves can easily lighten/darken an image. But this is achieved at the expense of altering the image's contrast. At the steepened part of the curve contrast is increased, while at the flattened part the contrast is reduced. Color and saturation can also be affected.
[{POST_SNAPBACK}][/a]
Yep – no free lunch...

Here’s another approach and definition for 'brightness' the threadopener might wish to try (can be also combined with a luminosity mask):
[a href=\"http://www.prophotohome.com/forum/colour-management/63048-just-tone-curve.html]http://www.prophotohome.com/forum/colour-m...tone-curve.html[/url]

DPL

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« Last Edit: January 07, 2008, 04:22:07 PM by standard_observer » Logged
John Sheehy
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« Reply #13 on: January 07, 2008, 04:30:52 PM »
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You are incorrect. Even if the source image is only 8-bit, you're still better off stitching to 16-bit mode immediately. If you start out with 256 levels and edit in 8-bit, after only a few edits (curves, levels, etc) you'll have significantly fewer than 256 levels left due to quantization and rounding errors. But if you switch to 16-bit mode immediately, you'll still have 256 levels left even after extensive editing and adjustments. Switching to 16-bit mode won't give you more than 256 levels, but it will let you keep all of the ones you already have.
[a href=\"index.php?act=findpost&pid=165603\"][{POST_SNAPBACK}][/a]

Well, to some extent, you can create more levels through editing.  Any sharpening, blurring, resampling, rotating, etc, will create more levels when an 8-bit image is edited in 16-bit mode.
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John Sheehy
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« Reply #14 on: January 07, 2008, 04:45:06 PM »
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I have some images that have ideal color and good black and white points, but need some overall lightening for printing on the new Epson Exhibition Fiber paper.

The two ways I know of to do this are to use either a curves adjustment layer, and bow the curve upward slightly leaving the endpoints fixed... or, use a levels adjustment layer and shift the midpoint slightly.  I am trying to understand the difference between these two approaches.  Is the levels approach like using a linear distribution on either side of the midpoint?

Curves can do anything Levels can do, but Curves allows more freedom (but requires more work to simulate a simple Levels gamma adjustment".

Quote
Any better approach that won't mess with color or saturation?  I am assuming the brightness/contrast control moves endpoints?
[a href=\"index.php?act=findpost&pid=164880\"][{POST_SNAPBACK}][/a]

Do the gamma adjustment in Levels, or more complicated adjustments in curves, but convert the image to Lab mode, and select only the lightness channel for editing.  You will change saturation and color far less than in RGB mode.
« Last Edit: January 07, 2008, 04:45:25 PM by John Sheehy » Logged
jule
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« Reply #15 on: January 07, 2008, 05:38:33 PM »
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I have some images that have ideal color and good black and white points, but need some overall lightening for printing on the new Epson Exhibition Fiber paper.

Glenn
[a href=\"index.php?act=findpost&pid=164880\"][{POST_SNAPBACK}][/a]
Just something else to consider, which you may have already done, so apologies if you have - your paper profile and monitor calibration.

You will need to check your soft proof against your print before you spend ages trying to lighten the image.

If it is a paper you have not used before, I would get a custom profile made, and ensure your monitor is calibrated, then make adjustments from there.

Julie
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Chris_T
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« Reply #16 on: January 11, 2008, 09:47:48 AM »
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Yep – no free lunch...

Here’s another approach and definition for 'brightness' the threadopener might wish to try (can be also combined with a luminosity mask):
http://www.prophotohome.com/forum/colour-m...tone-curve.html

DPL

--
[{POST_SNAPBACK}][/a]

Thanks for the reference. This is something new to me, and definitely worth giving that tone curve a try.

The post mentioned using blend if to preserve the highlight/shadows details, i.e. contrast, that can result from a flattened curve move. That's exactly what I currently do.

The post also referenced these actions:

[a href=\"http://www.xs4all.nl/~tindeman/raw/curve_tools.html]http://www.xs4all.nl/~tindeman/raw/curve_tools.html[/url]

If you have tried these, would appreciate your comments.
« Last Edit: January 11, 2008, 09:52:54 AM by Chris_T » Logged
Jonathan Wienke
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« Reply #17 on: January 11, 2008, 06:48:31 PM »
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Well, to some extent, you can create more levels through editing.  Any sharpening, blurring, resampling, rotating, etc, will create more levels when an 8-bit image is edited in 16-bit mode.

But those operations do not increase image quality the way starting out with more levels would. You're increasing the number of discrete data values, but that is not a free lunch.
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Peter_DL
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« Reply #18 on: January 12, 2008, 03:40:13 PM »
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Thanks for the reference. This is something new to me, and definitely worth giving that tone curve a try.

The post mentioned using blend if to preserve the highlight/shadows details, i.e. contrast, that can result from a flattened curve move. That's exactly what I currently do.

The post also referenced these actions:

http://www.xs4all.nl/~tindeman/raw/curve_tools.html

If you have tried these, would appreciate your comments.
[a href=\"index.php?act=findpost&pid=166514\"][{POST_SNAPBACK}][/a]
It happened that I was involved in the development of Simon’s curve tools back in 2005. So I guess I’m a bit biased regarding the idea of using HS-L* or HS-Y curves. However, for some considerations – ranging from 'simplicity' to an improved separation of tonality vs perceived color – I’ve put this approach aside.

For my purposes, initially quoted all-brightening sigmoidal RGB curve, ruled via Opacity and combined with a Luminosity mask, typically yields an eligible definition for Brightness. Other parameter such as in particular Contrast, Saturation and single Hues might deserve separate attention.

DPL

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« Last Edit: January 12, 2008, 03:48:49 PM by DPL » Logged
Chris_T
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« Reply #19 on: January 16, 2008, 08:34:32 AM »
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It happened that I was involved in the development of Simon’s curve tools back in 2005. So I guess I’m a bit biased regarding the idea of using HS-L* or HS-Y curves. However, for some considerations – ranging from 'simplicity' to an improved separation of tonality vs perceived color – I’ve put this approach aside.

For my purposes, initially quoted all-brightening sigmoidal RGB curve, ruled via Opacity and combined with a Luminosity mask, typically yields an eligible definition for Brightness. Other parameter such as in particular Contrast, Saturation and single Hues might deserve separate attention.

DPL

--
[a href=\"index.php?act=findpost&pid=166792\"][{POST_SNAPBACK}][/a]

It's good to hear directly from a developer.

Can you elaborate on the meaning and method of "an improved separation of tonality vs perceived color"?

Thanks.
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