What's the case for gamma today?

[digitaldog]

<blockquote>

<p>If the tools designed for you to see this data don't let you manipulate it in such a graceful way then it doesn't matter what state of encoding the data is in. Linear data is a bitch to edit.</p>

</blockquote>

 

<blockquote>

<p>I noticed everyone skipped over my demonstration of that point.</p>

</blockquote>

 

<p>Both points well taken! </p>

[jack_hogan]

<blockquote>

<p><em>If the tools designed for you to see this data don't let you manipulate it in such a graceful way then it doesn't matter what state of encoding the data is in. </em></p>

</blockquote>

<p>Tim, I am afraid that, as far as my beloved Capture NX2 is concerned, I am coming to that sad conclusion. However, that does not mean that if the software were properly designed it wouldn’t be better for it - and linear data would be just as easy to edit as gamma-corrected data.</p>

<blockquote>

<p><em>I noticed everyone skipped over my demonstration of that point.</em></p>

</blockquote>

<p>Yeah, I think it went over most of our heads: encoded with gamma 2.2, applied (not converted to) gamma 1.0, and displayed by the color managed browser of your choice. I’ve been thinking about gamma for a couple of weeks and I think I understand it quite well, but I haven’t gotten my head quite wrapped around that case yet. I wasn’t trying to prove one was better than the other. In fact that image was just to prove what a non-color-managed application would show. However, to compare apples to apples you should apply your test to the picture showing Photoshop displaying both the Gamma 1.0 and Gamma 2.2 pictures. I would expect both to be more or less the same (the Gamma 2.2 perhaps slightly better because it is slightly brighter ta start with) –this is the breakeven scenario after all.</p>

[joe_c5]

<p>Most digital cameras capture fewer than 65,535 electrons per subpixel, making 16-bit linear a good format indeed for digital raw images, theoretically allowing for no quantization error to be added by the encoding beyond what was already present in the electrons. So far, the limited dynamic range of the read circuitry has made 14-bit linear adequate for most cameras, where the 15th and 16th bit would have been mostly noise.</p>

<p>Also XYZ space is not the same as LMS (Long Medium Short) space, which should be better for matching since it is based more directly on the human eye than XYZ is. I believe that the ICC is aware of the limitations of XYZ space and is discussing eventually moving to a better connection space.</p>

<p>Finally, editing linear data appears to be as straightforward as using 32 Bits/Channel in Photoshop. I admit that this change in workflow is not free, but it seems to be practical in many situations.</p>

[digitaldog]

<blockquote>

<p>However, that does not mean that if the software were properly designed it wouldn’t be better for it - and linear data would be just as easy to edit as gamma-corrected data.</p>

</blockquote>

<p>True. But someone has to prove to the engineers and bean counters that the effort is worthwhile. Code is expensive to write. Someone has to document the new functionality and tech support has to be able to answer new questions that could arise. Someone has to justify the expensive in lieu of another feature that may be far more useful to the user base. If a tiny group of end users “feel” a linear encoding workflow is better (and they have to demonstrate this), its still an uphill battle to convince a product manager its worth doing. I think I suggested this pages back, in terms of talking to the Adobe Photoshop team. But before that even happens, well spoken and respected users have to first prove there is even a need and they have to do this in a pretty specific way, at last that’s been my experience with Adobe and a few other companies. Grassy knoll theories and saying publicly that a product is “broken” isn’t the right approach. That doesn’t even get the team to consider looking at the considerations which take place long before anyone with the power to implement a feature and look at the cost vs. benefit comes into play. <br>

Solutions looking for problems don’t fly.</p>

[joe_c5]

<p>I have determined experimentally that attempting to rebut similar statements tends to be unproductive, so I will not do so.</p>

<p>I caution others that this point of view appears similar to the ones that caused the Dark Ages. Most software vendors are constantly striving to improve their products, and I suspect that includes Adobe.</p>

<p>Finally, since it appears nobody else on Photo.net can or will back me against such views, I am afraid I do not fit in here and intend to head elsewere.</p>

<p>Farewell to all.</p>

[digitaldog]

<blockquote>

<p>Most software vendors are constantly striving to improve their products, and I suspect that includes Adobe.</p>

</blockquote>

<p>As an Alpha and Beta tester I can say with most certainty that Adobe <strong>strives to improve their products!</strong> Some think that they don’t go far enough because their pet project feature isn’t implemented but they haven’t thought very far as to why. Or they simply do a very poor job of communicating to the company not only their needs but think their needs have a higher value than other users needs. Or they think their needs are based on a real need! </p>

<p>Over on Luminous Landscape is an interesting discussion about soft proofing and the role of the Gamut Warning. One user suggested that it would be useful if the Info palette, that today includes a feature that provides the RGB or CMYK values of the conversion to the color space from the customize proof setup were to optionally allow him to see this in Lab. His reasons for doing so seem quite sound, the implementation is hardly big engineering. Its an interesting idea and he’s done a good job expressing why such functionality would be useful (and more useful than a legacy feature, gamut warning, that’s really just around because there’s more work in removing it). Anyway, its a good conversation and one that might actually have some possibility of getting the ear of Adobe engineers! </p>

<blockquote>

<p>Finally, since it appears nobody else on Photo.net can or will back me against such views, I am afraid I do not fit in here and intend to head <em>elsewere</em>.</p>

</blockquote>

<p>Ah, so its about getting backing otherwise you’ll leave the sandbox? Well OK then. </p>

[cliff_rames]

<blockquote>

<p>Cliff, can you prove this with a screenshot.<br>

Make sure you assign your custom display profile to the screenshot and convert to sRGB for us to see what you see on your hardware calibrated display.</p>

</blockquote>

<p>I don't see the point of a screen shot.</p>

<p>Here is a simple image that demonstrates the concept - you can easily duplicate for yourself.</p>

<p>The top third is the original ramp<br>

The second third has the black point lowered in sRGB<br>

The third third has the black point lowered in sRGB with a linear gamma.</p>

<p>Clearly, lowering the black point in gamma has an effect that extends far up along the tonal range.</p>

<p>I find that setting the black point in linear looks better on real images and contributes to a 3D look.</p><div></div>

[jack_hogan]

<p>Joe C, I for one would like you to stay. I find your contributions interesting and as competent and well informed as any poster who is not a color scientist or does not do this as part of their full time job can be. I do agree that Photo.net can come across as holier than thou and pompous at times, but in the end they are good folks.</p>

<blockquote>

<p>Finally, editing linear data appears to be as straightforward as using 32 Bits/Channel in Photoshop.</p>

</blockquote>

<p>I am not sure I understand. If you mean that with the increased resolution of 32 bits it doesn't really matter whether the underlying data is linear or gamma corrected, I agree entirely.</p>

[cliff_rames]

<p>Joe C wrote:</p>

<blockquote>Also XYZ space is not the same as LMS (Long Medium Short) space, which should be better for matching since it is based more directly on the human eye than XYZ is. I believe that the ICC is aware of the limitations of XYZ space and is discussing eventually moving to a better connection space.</blockquote>

<p>LMS is just another linear transformation of XYZ (http://en.wikipedia.org/wiki/LMS_color_space) and will behave the same as linear ICC working spaces with regard to color mixing. Yes, LMS or "cone space" is important for chromatic adaptation or white balancing, but that's not what being discussed in this thread.</p>

[hangthemoon]

<p>I like to take photographs. I am pleased with the incredible technology we have today. I shoot with a canon 5d mark 2 and print on an Epson 7900. The prints rival darkroom prints from 4x5 negatives (we have done tons of testing).<br>

This is interesting reading and valid points are being made.<br>

I am blessed to sell my prints regularly even in this economy. Rarely do I sell prints to other photographers. Most of my clients are educated enough about photography to know a good print from a bad print even if they do not technically know why.<br>

I believe that the advances in digital photography have progressed to the point where I can just take pictures and have fun.<br>

My advise is just take photographs, print, and enjoy.<br>

I have never lost a sale on a print due to any of the technical stuff you guys are discussing. It does sound like, however, that you know a lot about it.</p>

 

[Tim_Lookingbill]

<p>Cliff, thanks for making the effort to post those gradients.</p>

<p>I tried out your suggestion of setting black point in linear space using Photoshop's Exposure tool on my test image I posted earlier in this thread. It does gracefully and gradually open up shadows without inducing abrupt and grainy transitions to black as it does in a gamma encoded space. But as I noticed in your gradients using this method, it has the opposite effect on highlight tones transitioning to absolute white.</p>

<p>The X-rite CC chart white patch kept clipping adjusting the Exposure and Gamma slider after first setting Offset for black point just to get a correct to scene look I could get working in ACR. The image did have a 3D feel to it but the grass in that test shot ended up being too dark for a scene that was lit by 10 AM direct sunlight.</p>

<p>However, I was amazed to find the gray patches and color Lab readings were close to dead on using this method which I couldn't get in ACR without making the entire image look slightly dark and dim. </p>

[jack_hogan]

<p>Cliff, I assume you are talking about setting the black point in Photoshop, not in a raw converter, correct? Assuming so, after you have set your black point in Gamma=1, do you switch back to a gamma encoded space for further processing?</p>

<p>@Scott: I like your eye, man. As for myself, I am afraid that the old saying applies:'Those who can, do. Those who can't' ... talk about it.</p>

[cliff_rames]

<p>Tim, I'm glad that you're able to see the effect! I'm not sure what you mean about the highlights, and I only see a small, manipulated Macbeth shot of yours on page 10 of this thread, so I can't try to duplicate what you're seeing with the grass.</p>

<p>Jack, I'm talking about Photoshop, but (without knowing what the raw converter Black controls really do under the hood) assume it also applies to raw converters that work on the camera data linearly.</p>

<p>If I'm starting with a linear file, I usually just keep it in linear until there is a reason to convert to gamma. I use a default working space with ProphotoRGB primaries and gamma 1. Once you make yourself such a working space profile, working in linear is easy. If I have some random 8bit sRGB file, I switch it to 16bit mode and convert to the linear working space. But as mentioned before, some things actually work better in gamma space, such as Curves - also some noise-reduction and sharpening methods. It all depends. If you work in 16 bits I don't think it really hurts even to switch back and forth.</p>

[Tim_Lookingbill]

<blockquote>

<p>Tim, I'm glad that you're able to see the effect! I'm not sure what you mean about the highlights, and I only see a small, manipulated Macbeth shot of yours on page 10 of this thread, so I can't try to duplicate what you're seeing with the grass.</p>

 

</blockquote>

<p>See the screenshots below. I'll follow with a 100% crop of shadow detail made by the two edit methods.</p>

<p>I think the cause for the abrupt clipping of the CC chart white patch using the Exposure slider in linear space is probably due in part in that I had to assign a 1.0 gamma profile to a 1.8 gamma encoded image out of ACR. I adjusted the Exposure tool so that the white patch only maxed out at 250 RGB when converting to sRGB for the web. In linear space it read 241 ProPhoto 1.0 gamma RGB or 98 L in Lab space read from Photoshop's info palette.</p><div></div>

[Tim_Lookingbill]

<p>Here's the shadow detail crop for the two different processes.</p><div></div>

[cliff_rames]

<p>Tim, I'm confused by your process. I'm not convinced you are working with a linear file. You describe <em>applying</em> rather than <em>converting</em> to the linear profile, then applying additional gamma in the Exposure tool.</p>

<p>You should just <em>convert</em> the output from ACR to the ProphotoRGB Linear profile - that's all you need to do to have a linear file. Then you can adjust the black point with exposure, levels, curves, whatever you want - all tools will be working in linear.</p>

<p>Or am I missing something due to turkey-induced grogginess...</p>

[Tim_Lookingbill]

<blockquote>

<p>You should just <em >convert</em> the output from ACR to the ProphotoRGB Linear profile - that's all you need to do to have a linear file.</p>

 

</blockquote>

<p>Even if the data coming out of ACR has been encoded into 1.8 gamma ProPhotoRGB color space? </p>

<p>I tried what you suggested by converting directly from 1.8 gamma ProPhotoRGB to 1.0 gamma ProPhotoRGB and got pretty much the same dim low contrast rendering only this time I prevented the white from clipping by reversing the Exposure settings to...</p>

<p>Exposure=+1.0<br>

Offset=-.0012 (black point)<br>

Gamma=1.10</p>

<p>No other slider combinations would give me the contrast and vibrance I got in ACR. And I'll admit I'm not too clear on how to use the Exposure tool. I haven't read the instructions if there are any. I guess I should google it. Maybe someone came up with a sure fire method. Hope their definition of linear is the same as what I get out of ACR.</p>

<p>I really suspect imaging software's definition of linear as it relates to its editing tools are not all engineered the same or are guaranteed to work within different imaging software brands or even within their own brand.</p>

<p>I have no idea what defines linear data, what it's suppose to look like on a 2.2 gamma display or how to know if it actually is linear as defined by what came off the sensor.</p>

<p>I have a feeling those who write imaging software that claim linear output are reverse engineering their programming methods to match up to what ever their demosaicing software gives them. Whether that's in a linear space is anyone's guess.</p>

[cliff_rames]

<blockquote>

<p>Even if the data coming out of ACR has been encoded into 1.8 gamma ProPhotoRGB color space?</p>

</blockquote>

<p>Definitely.</p>

 

<blockquote>

<p>I tried what you suggested by converting directly from 1.8 gamma ProPhotoRGB to 1.0 gamma ProPhotoRGB and got pretty much the same dim low contrast rendering only this time I prevented the white from clipping by reversing the Exposure settings to...</p>

</blockquote>

<p>When you convert to the linear profile the screen appearance should not change at all. Photoshop will display it properly. Don't know why you have a "dim low contrast rendering."</p>

<blockquote>Exposure=+1.0<br /> Offset=-.0012 (black point)<br /> Gamma=1.10</blockquote>

<p>All three of those settings are affecting the black point. The Gamma setting is making it non-linear. Suggest you set exposure, then offset. Don't change gamma for now.</p>

<blockquote>No other slider combinations would give me the contrast and vibrance I got in ACR.</blockquote>

<p>You're asking too much from the Exposure tool - it doesn't replace all of the ACR tools. Concentrate on the shadows - try matching an ACR rendering that has only the exposure and black point adjusted.</p>

<p>The idea is simply that some flare light can be subtracted from images in a realistic way by setting black point in linear space. Setting black point in certain raw converters accomplishes this. It can also be done with the Exposure Tool which apparently operates internally in linear no matter what the gamma of the color profile. Or the image can be converted to a linear space to use Levels, Curves, etc., for setting the black point.</p>

 

[digitaldog]

<blockquote>

<p>I think the cause for the abrupt clipping of the CC chart white patch using the Exposure slider in linear space is probably due in part in that I had to assign a 1.0 gamma profile to a 1.8 gamma encoded image out of ACR. </p>

</blockquote>

<p>I’d think you’d want to encode out of the converter using a 1.0 TRC working space (modified in Photoshop), <em>not</em> assign this to a 1.8 TRC image. You can’t do that with ACR, its hardwired for four working spaces but could with Lightroom. </p>

<blockquote>

<p>You should just <em>convert</em> the output from ACR to the ProphotoRGB Linear profile.</p>

</blockquote>

<p>Right, except it will not allow this. Lightroom can. Just build the modified profile and select it in the Export dialog. Any RGB color spaces can be selected from the popup after selecting “Other” and placing a check box next to the profile you want to use.</p>

[Tim_Lookingbill]

<p>Cliff, the test image doesn't change when I convert to G1 ProPhotoRGB. Sorry for not being more clear. I shouldn't try to say everything in one sentence to avoid getting word reference mix ups.</p>

<p>It looks dim AFTER I tried to make the image look the best it can using the Exposure tool while keeping the white patch from clipping. See below the dim look I'm referring to from setting Exposure to 1.12 and Offset -.0014. Lab reading for CC chart white patch is maxed at 98L or<br /> 252RGB for sRGB space.</p>

<p>It still looks dim and shadow definition (shadow "foggies"/flair elimination) isn't better than what I got in ACR. This seems to be way too much trouble than it's worth.</p>

<p>This experiment did get me to try out zero-ing out my ACR settings to get a non-gamma corrected (darkish) linear preview so I could come up with different curves without relying only on sliders and default contrast curve.</p>

<p>This method DOES open up a lot of shadow detail while keeping noise to a minimum just by grabbing a point on the curve at 5/5 and just pushing up creating a sort of gamma shaped curve. I can then apply further tweaks along this curve in shaping contrast and definition. Come back with slight tweaks to Recovery/Fill and Contrast and Clarity and I'm done. It seems to be a quicker more methodical way of working than my usual back and forth tinkering. I've been relying too much on Recovery/Fill to correct these types of high contrast shots and getting halo's along light/dark edges. This linear approach in ACR minimizes the use of these tools.</p>

<p>Unfortunately these settings only work on this test image and others I took at the same time of the same scene just at different angles. I was hoping to find a one size fits all setting with this linear approach so I don't have to edit every one of my landscape and other outdoor shots from scratch. Applying saved presets creates more work than just starting from scratch. Bummer!</p>

<p>Thanks for the patience and feedback on this subject.</p>

<p>Back to the digital PP grind stone. A cold front passed through making for one of those super crispy, clear, not a cloud in a gorgeous blue sky days and just shot 90 Raws today. All of them high contrast and the presets from this test image make them flat and washed out. But I did use a different lens, so I guess I need to create a DNG profile for that.</p><div></div>

[cliff_rames]

<blockquote>This seems to be way too much trouble than it's worth.</blockquote>

<p>Tim, I think you're misunderstanding me.</p>

<p>I am not suggesting that you use the exposure tool instead of the tools in ACR. When you are setting the blacks in ACR, you are already doing it linear! So for your particular workflow using ACR, you're not going to see any advantage. You can thank the wise Adobe engineers for that.</p>

<p>Once outside ACR, and you want to perform a linear operation, you can just use Exposure, without having to change to a linear color space! Once outside of ACR and you have to tweak the black point, you can get a result similar to what ACR gives by your choice of tool - how is that any "trouble?"</p>

<p>But the point again in the context of the thread is that the results of setting black point in linear is visibly different vs. setting it in gamma.</p>

<p> </p>

[Tim_Lookingbill]

<p>Cliff, I finally figured out what you were trying to communicate. The light bulb just went off for me and now I see exactly what you're talking about. Sorry for the misunderstanding.</p>

<p>Really! I truly am! I could kick myself. I've been going about this the wrong way all this time.</p>

<p>I couldn't believe the results I got using the Exposure slider to open up NORMALIZED (close to finished) previews out of ACR. </p>

<p>I just now remembered you mentioning this it seems years ago over at the Adobe forums discussing linear rendering out of ACR for DNG camera profile building. The meaning of linear data and its associated preview confused me from my scanner days and from other Raw converters that have this setting. You're saying CONVERT to a linear space. The preview doesn't have to reflect a linear rendering for setting black point.</p>

<p>I had always assumed you were talking about using the Exposure slider on "linearized"=(zero'ed out ACR settings) that give the familiar darkish previews in trying to open up the shadows. You're talking about using the Exposure slider to open up shadow clarity instead of relying heavily on ACR's Fill slider or pinch points in the Curve tool.</p>

<p>You're right! I just used the Exposure tool on a <em>finished</em> image (see crop sample below) that had given me trouble a while back where I just gave up and left some cluttered rock detail along a river bank cast in dark shadow remain dark and murky. Highlight/Shadow tool is too confusing and gives abrupt transitions if you go too far. The Exposure tool seems to have given me an extra 1/2 to a full stop of useable dynamic range that would posterize using curves in ACR.</p>

<p>ACR's Contrast and Fill sliders reach too far into the rest of the tonal scale of the image where they end up canceling each other out. The Exposure tool behaves much more differently. </p>

<p>Thanks for the tip and sorry for the misunderstanding. </p>

<p>Happy Holidays!</p><div></div>