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Author Topic: Your Curves  (Read 146858 times)
Guillermo Luijk
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« Reply #140 on: August 01, 2007, 06:09:45 PM »
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Oops! I made a mistake, this is why not all space rockets reach the Moon. The formula to implement the curve in test 3 is not completely right, so bright didn't reach the maximum. This is the right expression:

HSVtoRGB H, S, IIf(V <= 0.5, 2 * V * V, 0.5 + ((2 * (IIf(V < 0.5, 0.5, V) - 0.5)) ^ 0.5) / 2), R, G, B

And the result (this was B constrast preserving H and S):


Same curve in PS Luminance mode (yes, saturation changes as Gloria says Mark, it's Hue here that doesn't change):


Same curve in PS Normal mode:


_________________

The look improves noticeably with the correction (I am talking about the first picture now), but it's still far from the result achieved with PS Luminance blending mode. Just need to look at the sky, far crops or flower textures (BTW they are not tulips, they are amapolas. Don't know the name in English).
« Last Edit: August 01, 2007, 06:15:17 PM by GLuijk » Logged

Mark D Segal
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« Reply #141 on: August 01, 2007, 06:52:40 PM »
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PS Luminance mode[/b] (yes, saturation changes as Gloria says Mark, it's Hue here that doesn't change):

[a href=\"index.php?act=findpost&pid=131091\"][{POST_SNAPBACK}][/a]

Well, maybe it does in the images you have displayed, but IN PRINCIPLE it is not meant to change. You may verify this at any number of the more serious photography websites which provide tutorial information, or from standard reference books, such as:

Real World Photoshop CS2 (Fraser & Blatner) page 357: "... Luminosity is the inverse of Color. It creates a result color with the hue and saturation of the underlying layer and the luminosity of the overlying layer."

Photoshop Masking and Compositing (Eismann), page 199: " In this example the Curves adjustment improved the image contrast, but it also over-saturated the little girl's sweater.....By changing the Curves layer blending mode to Luminosity, the contrast correction is maintained while the false saturation problem is negated..."
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Mark D Segal (formerly MarkDS)
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laughfta
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« Reply #142 on: August 01, 2007, 11:15:10 PM »
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Well, maybe it does in the images you have displayed, but IN PRINCIPLE it is not meant to change. You may verify this at any number of the more serious photography websites


I don't quite know what to think

Back in the day, (Post #75) Guillermo in his tests came to this conclusion about PS Luminosity:

"What really happens (I have tested some pixels with your loved probes Mark lol):
- Hue is preserved in all pixels
- Saturation is reduced in those pixels where Bright is increased
- Saturation is increased in those pixels where Bright is reduced"

When I look at an image in PS, with a curve contrast layer in luminosity mode, a color sampler point set using 'point sample' so that one can make an accurate sample, and turning the layer on and off I measure this: In the lighter areas, the saturation is reduced, in the darker areas the saturation is increased, and in the middtones, it stays exactly the same.  Theoretically, everyone can be right.  

Does anyone else measure something different?
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Mark D Segal
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« Reply #143 on: August 02, 2007, 06:59:31 AM »
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Not everyone can be right - would be nice, but not to be. If you drew the "S" around the mid-tone you tested (such that the mid-tone were positioned roughly in the middle of the "S"), then of course that value would have experienced very little movement so you wouldn't get much of a change of anything. Your findings for the brights and the darks, however, do not cohere with the principle. Using a 3*3 or 5*5 sample grid would be preferable to rule out anomolies but somehow I doubt that is really the issue here. I have just completed another set of exercises to test a hypothesis related to how CR handles areas of bright pre-dominant colour, where I did a considerable set of measurements, and I too am getting variability between brightness and saturation changes. I think while the principle of saturation neutraility is supposed to be preserved by the manner in which Photoshop is programmed, from what I have been informed, the problem is more likely to be imperfections in the HSB calculations themselves. In the final analysis, as photographers, our objective is the appearance of the photographs - hence I've come to the conclusion that the pixel-value accounting, while academically interesting, is less important than whether the photograph does what we want it to do.
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Mark D Segal (formerly MarkDS)
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Guillermo Luijk
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« Reply #144 on: August 02, 2007, 07:33:40 AM »
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I would like to point that the behaviour of the Saturation in PS Luminance curves (and with Saturation I mean the mathematical definition defined in the HSB colour model; the degree of agreement between this model and human eye perception is another analysis to do), is not exactly S increase in dark areas, and S reduction in light areas. It's S increase in areas that get darker, and S reduction in areas that get lighter, when applying the particular curve.

- In the most common s-shaped contrast curve, where dark areas are made darker, and light areas are made brighter, this behaviour translates as: more saturation in dark areas, less saturation in bright areas.
- But if we took an inverted s-shaped curve (contrast reduction), the behaviour would be dark areas would get less saturated, and light areas would get more saturated.
« Last Edit: August 02, 2007, 07:37:32 AM by GLuijk » Logged

Kenneth Sky
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« Reply #145 on: August 02, 2007, 07:47:42 AM »
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I fear to tread where angels walk. I have followed this thread as I suspect most of us with bewilderment. All of these mathematical models don't take in the perception of a photograph by the eye and its interpretation by the cortex. If we could create a standardized ambience for viewing prints and then get a statistically signifigant number of viewers to report the just noticeable differences that all of these mathematical models make, it would make a lot more sense to a lot of us. I am not belittleing this discussion, but I am saying that with my post-doctoral education I am still getting confused as to how this helps me make a better print.
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laughfta
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« Reply #146 on: August 02, 2007, 07:50:13 AM »
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I think while the principle of saturation neutraility is supposed to be preserved by the manner in which Photoshop is programmed, from what I have been informed, the problem is more likely to be imperfections in the HSB calculations themselves. In the final analysis, as photographers, our objective is the appearance of the photographs - hence I've come to the conclusion that the pixel-value accounting, while academically interesting, is less important than whether the photograph does what we want it to do.

I agree. My goal is to make an excellent final print of the image. If anything, this exercise just showed that whatever Adobe did with the luminosity mode, it is an improvement to making a contrast curve with only brightness. (At least in this case, at least to me)

The one area that I noticed as being possibly problematic to a final print, is the highlights in the sky, some seem to be either blown or approaching blown in the PS Lum and normal version. They look fine in the original, and in the B version with the same contrast curve. But it may be hard to discuss this if it isn't happening.  I guess if I was developing a raw image in ACR, I would take care to correct this with one of the many ways available (if it were, indeed, happening). I would dearly love an info palette in ACR.
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Mark D Segal
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« Reply #147 on: August 02, 2007, 08:29:17 AM »
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I fear to tread where angels walk. I have followed this thread as I suspect most of us with bewilderment. All of these mathematical models don't take in the perception of a photograph by the eye and its interpretation by the cortex. If we could create a standardized ambience for viewing prints and then get a statistically signifigant number of viewers to report the just noticeable differences that all of these mathematical models make, it would make a lot more sense to a lot of us. I am not belittleing this discussion, but I am saying that with my post-doctoral education I am still getting confused as to how this helps me make a better print.
[a href=\"index.php?act=findpost&pid=131164\"][{POST_SNAPBACK}][/a]

Kenneth - of course underlying everything we do in these programs is a lot of math. Do users need to understand the math to use the programs? No. Is it good for users to gain a more precise appreciation of the behaviour of the programs' tools - Yes. Again, one doesn't need to know the math to do this, but some insight into how the numbers describing the results come out is a useful complement to the essential thing - as you say - the perceptual quality of the photographs; hence my comment in my previous post.  I think it helps you make a better print to know roughly how saturation will behave as you adjust a curve - of course you can see it when it happens -and all the more so if you are aware of the effect in the first place.
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Mark D Segal (formerly MarkDS)
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laughfta
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« Reply #148 on: August 02, 2007, 08:34:56 AM »
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... I am still getting confused as to how this helps me make a better print.

There is something about PS that kind of sucks you in, I think:) You start out trying to clone out some imperfection, someone shows you how to  use various blurs, layers and  modes and it looks clearly better, then  you try converting it to Black and White, and the techniques pile up...

I have reached critical mass with techniques, and feel the need to understand the principals behind them that make them work. One reason is that I would remember them better, another is that I would be able to evaluate them to some extent without trying each and every one on every problem image. Most importantly I would be better able to modify and create my own workflow, which has to start in ACR.

But I do get carried away, though unlike Guillermo and Mark and many others, I am hanging on by the skin of my teeth in this discussion.

So, Mark, how do you like that target tool in CR for modifying the curve?  
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Mark D Segal
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« Reply #149 on: August 02, 2007, 08:35:08 AM »
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I would dearly love an info palette in ACR.
[a href=\"index.php?act=findpost&pid=131165\"][{POST_SNAPBACK}][/a]

I would like this too. To get it, one would need to make a feature request to Adobe along with an argument for why it would advance the usefulness of the program.
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Mark D Segal (formerly MarkDS)
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Kenneth Sky
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« Reply #150 on: August 02, 2007, 08:47:49 AM »
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Mark
I agree. Just bring the discussion down to the level us "plebes" can understand and use, i.e. in a practical sense. The science is wonderful but I would like to know how each model advances the art. For a lot of us, digital post processing has just recently come out of the "black box" with recent iterations of Photoshop and the introduction of Lightroom. I guess I'm pleading for the KISS principle.
Ken
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Guillermo Luijk
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« Reply #151 on: August 02, 2007, 08:52:10 AM »
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Vey often I hear "I like to do in ACR all possible adjustments so that I save time in PS". Maybe I am wrong, but this aseveration doesn't seem brilliant to me; I could tell this person "I like to do in PS all possible adjustments so that I save time in my RAW developer":

I know this will not suffice (almost) anyone, but as I was commenting in other thread in this sub-forum I use DCRAW as a RAW developer, and do all adjustments once in PS:
- Exposure correction
- Camera profile
- Colour profile conversion and gamma
- Constrast and saturation
- Noise reduction
- Sharpening
...
I only miss from ACR the good noise reduction ability, which really works well.

I think having more and more features in the RAW developer only makes sense if you really wanto to get rid of PS, and end your processing in the RAW developer. But if the point is to go anyway to PS, I think this feature duplication is not useful to simplify and hence improve anyone's workflow.

I share the point of Angela that knowing how a particular of tool internally works can lead you to know if it is adequate for a certaing problem, saving testing times. A very typical case for this is the discusion: "sharp mask vs high pass filter". All sharpening techniques are based in high pass filtering which is the common tecnique to increase high spatial-frequency details; so they are basically the same. Use the one that makes you feel more confortable, but don't think one is better than the other.
« Last Edit: August 02, 2007, 08:55:50 AM by GLuijk » Logged

digitaldog
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« Reply #152 on: August 02, 2007, 09:04:32 AM »
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Vey often I hear "I like to do in ACR all possible adjustments so that I save time in PS". Maybe I am wrong, but this aseveration doesn't seem brilliant to me; I could tell this person "I like to do in PS all possible adjustments so that I save time in my RAW developer":

This gets back to the guru who only understands Photoshop and doesn't understand rendering.

A Raw processor is a rendering engine. Its not a correction tool so to speak as we have in Photoshop. With Photoshop, you've got rendered, baked pixels. You can fix them but you can't re-render them. A Raw processor isn't as much a 'correction' tool as a rendering tool. There's a difference! Raw has no color, you create the color and tone from essentially Grayscale data. You do this by building metadata instructions that will eventually be used to build colored pixels that you may further need to edit in a pixel editor (Photoshop).

The beauty of metadata rendering is you have all the original data to work with that the camera captured.

You can build as many sets of instructions to render as many pixel based documents you wish in a truly non destructive manner.

You have linear encoded, high bit, potentially very wide gamut data to render. After rendering, you get what you get, you can't really put all that toothpaste back into the tube.

I'm sure I'm missing other useful features of instruction based rendering from Raw, but the big point is, its not pixel editing in Photoshop by a long shot. For this reason, the idea of doing as much work in CR than Photoshop makes a heck of a lot more sense in terms of quality, toolset and speed. Naturally there are all kinds of operations that can't happen until one has a pixel based document. Then Photoshop is king. Different tools for different tasks. Not the same as looking at these processes as a hammer in search of a nail.

It is here the guru doesn't get it. Worse, he says the toolset is unfit for professional use due to sloppy math despite Mark's continuing efforts to show that isn't at all the case. Meanwhile, getting Raws from the guru to illustrate his point have gone nowhere. Could be due not to sloppy math but sloppy rendering techiques? Where's the spreadsheet proving the faulty math?
« Last Edit: August 02, 2007, 09:13:45 AM by digitaldog » Logged

Andrew Rodney
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« Reply #153 on: August 02, 2007, 09:12:30 AM »
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I guess I'm pleading for the KISS principle.

For me, its about making the image look the way I want it to. The math isn't important after awhile.

For CR and LR, working top down, left to right is the KISS approach and design.
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Mark D Segal
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« Reply #154 on: August 02, 2007, 09:41:01 AM »
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Mark
I agree. Just bring the discussion down to the level us "plebes" can understand and use, i.e. in a practical sense. The science is wonderful but I would like to know how each model advances the art. For a lot of us, digital post processing has just recently come out of the "black box" with recent iterations of Photoshop and the introduction of Lightroom. I guess I'm pleading for the KISS principle.
Ken
[a href=\"index.php?act=findpost&pid=131175\"][{POST_SNAPBACK}][/a]

Ken, Just for the record, I am not a programmer and not a digital imaging mathematician - by a long shot. The way I approach this is to do carefully controlled experiments that allow me to evaluate outcomes as a result of adjustments using one tool at a time (or more depending on the objective) in a manner that I can associate the character of the outcome with the nature of the adjustment. For me, the final arbiter is what it is for you - how does the image look? I use the numbers to corroborate or amplify. I also find the numbers in the info palette very handy for making the adjustments. They do help keep our eyes "honest". I do hope you found the discussion in my paper "down to earth" enough to be useful.
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Mark D Segal (formerly MarkDS)
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« Reply #155 on: August 02, 2007, 09:54:36 AM »
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For this reason, the idea of doing as much work in CR than Photoshop makes a heck of a lot more sense in terms of quality, toolset and speed. Naturally there are all kinds of operations that can't happen until one has a pixel based document. Then Photoshop is king. Different tools for different tasks. [a href=\"index.php?act=findpost&pid=131180\"][{POST_SNAPBACK}][/a]

Andrew,
I think we are all in favour of as much non-destructive editing as possible. I notice that CS3 allows for more editing options in 32 bit than CS2. Levels have now been included on the sparse list, but not curves yet.

Just how significant is this non-destructive aspect of editing in ACR? Are we talking about a degree of difference equivalent to Photoshop editing in 16 bit as opposed to 8 bit? Or perhaps converting an image that's originally in 8 bit to 16 bit for editing purposes?

There appears to be a progression towards more editing of pixel based documents in 32 bit mode. How would doing all editing in 32 bit mode, in Photoshop, compare with the so-called non-destructive editing with ACR curves?
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Mark D Segal
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« Reply #156 on: August 02, 2007, 09:58:40 AM »
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This gets back to the guru who only understands Photoshop and doesn't understand rendering.

A Raw processor is a rendering engine. Its not a correction tool so to speak as we have in Photoshop. With Photoshop, you've got rendered, baked pixels. You can fix them but you can't re-render them. A Raw processor isn't as much a 'correction' tool as a rendering tool. ........

The beauty of metadata rendering is you have all the original data to work with that the camera captured.

You can build as many sets of instructions to render as many pixel based documents you wish in a truly non destructive manner.

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

It is here the guru doesn't get it. Worse, he says the toolset is unfit for professional use due to sloppy math despite Mark's continuing efforts to show that isn't at all the case. Meanwhile, getting Raws from the guru to illustrate his point have gone nowhere. Could be due not to sloppy math but sloppy rendering techiques? Where's the spreadsheet proving the faulty math?
[a href=\"index.php?act=findpost&pid=131180\"][{POST_SNAPBACK}][/a]

Andrew, OK - technically all correct - as usual - but to add a bit of semantics, I would suggest that the rendering instructions we build into the file are also "corrections" or "adjustments" - except they aren't correcting or adjusting pixels, and the beauty of the new tools is that we can now do so much more image editing in a non-destructive manner, why we recommend doing as much as feasible in CR before rendering into Photoshop, where as you say, it is king for doing things CR or Lightroom cannot do.

As for getting images from the Guru, I believe the images he refers to are the ones on the CD-ROM which comes with the Guru's book and there are Terms of Use. So you need to buy the book in order to have the images. Needless to say, I own a copy of the Guru's book, because eventhough I may disagree with a lot of what he says about raw rendering, there's much other useful stuff in the book.

So being entitled to download and play with the images in Chapter 16 related to raw conversion, I have run these images through CR 4.0 on my computer,  and I believe that I get great results (and in two cases I believe arguably better than his) with a minimal amount of work in CR4.0 alone. Before I share any of this stuff beyond my computer I need to verify the legal rights involved. Meanwhile, I'm using my own images where there are no legal problems. There may be more to say about this anon.  But I agree with you - it would be great if he were to share openly the raw images he believes CR either can't correct properly or CR "damages" and then we can have a more specific dialogue on an open forum with him about those very images.
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Mark D Segal (formerly MarkDS)
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Mark D Segal
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« Reply #157 on: August 02, 2007, 10:16:19 AM »
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So, Mark, how do you like that target tool in CR for modifying the curve? 
[a href=\"index.php?act=findpost&pid=131172\"][{POST_SNAPBACK}][/a]

I'm using CR 4.0 in Windows and there is no targeted adjustment tool there. It is in Lightroom and I think it is very intuitive and helpful.
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Mark D Segal (formerly MarkDS)
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Guillermo Luijk
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« Reply #158 on: August 02, 2007, 10:24:05 AM »
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I am sorry to get back to a bit technical terminology, but I don't understand very well what is understood by "non-destructive edition". It means you can undo? It mens you even don't need to undo an action to make a new adjustmente without any quality loss? what is it?

Performing operations such as curves in PS with mask layers provides this kind of control. If you load a plain developed RAW (for instance developed using DCRAW), the only parameter applied in a "destructive" manner (and now I mean you cannot change it without going back to the original file) is white balance. And even in that case you can save all your set of Curves, Levels, or wathever mask layers in use over the present image.

So I don't see a clear advantage in the theoretically "non-destructive" processing found on most RAW developers (or renderers or whatever they are called).
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« Reply #159 on: August 02, 2007, 10:59:13 AM »
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I am sorry to get back to a bit technical terminology, but I don't understand very well what is understood by "non-destructive edition". It means you can undo? It mens you even don't need to undo an action to make a new adjustmente without any quality loss? what is it?

Depends on who you ask. Marketing folks use the term incorrectly IMHO. No, undo isn't non destructive nor is saving out a copy. We've had this since day one on computers, nothing new or special.

IF you edit an existing pixel value, there's some 'damage' due to rounding errors, greatly reduced using high bit data. If you don't alter the values, there's no edit (so its not non destructive editing). Saving a copy, having adjustment layers which postpone the pixels undergoing a numeric change are NOT non destructive. Raw rendering truly is. The Raw data is never touched or altered. The result is a new, pixel based image that has yet undergone no number changing pixel edits.

The idea of an Adjustment layer being non destructive isn't correct. IF you flatten the image or print the document, the edit is stamped somewhere (even if the term stamped applies to data being sent to a printer). So I don't consider this non destructive. Nor do I find using metadata edits on existing rendered images in CR or LR non destructive. If anything, it might be more destructive (or less) depending on the edits. An existing rendered image in CR and LR still need to be converted to high bit, linear encoded ProPhoto RGB just to apply any tweak from the metadata instructions.
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Andrew Rodney
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