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04-22-2014, 07:22 PM   #1
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First attempts at high-key and low-key: question about histograms

Hi,

Yesterday I tried my hand at two quite extreme high-key and low-key images: a marble sculpture shot against a white background and a black clay mask shot against a black background. This was my first attempt, so excuse my lack of expertise; I am posting the images to illustrate my question. I will formulate it as a high-key question, but I had the same problem with the low-key attempt (only backwards, of course).

The problem amounts to this: my white looks less white than I would like it to, and if I try to make it whiter, the histogram is clipped. Now, everything I read about high-key told me the steep spike to the right of the histogram would end quite abruptly, almost exactly in the lower right, as steeply as possible, as long as it was not clipped; however, if I post-produce the image to have a histogram that looks somewhat like this, I get highlight warnings, blown highlights and a clipped histogram. The only way I could get rid of all this was to use curves to bring all my whites to under 250 or thereabouts, but in this case my histogram will not fully reach to the right -- the spike will come down abruptly at the right, but there is still going to be a narrow, fully unused histogram space to the extreme right, since no pixel in the image goes above 250 (or thereabouts).

Same thing happened with low-key attempt: I had to bring all my blacks to above 5 (or thereabouts) so I wouldn't get shadow warnings, all-black shadows and a clipped histogram. To avoid this, my spike wouldn't start to the very left, but only after an empty unused space.

I have also seen video tutorials in which high-key portraits may be worked so as to have a fully blown-out, plain white background while retaining all details in the subject. This is not what happens in my high-key attempt: the first thing to blow out are the reflexes in the sculpture itself, and only then the background. All-black shadows in the low-key attempt also start in the chin of the mask and go up the middle line before any background shadows are clipped.

What am I doing wrong? Should I have illuminated the backgrounds differently? Maybe used a different post-production approach? Any help will be much appreciated.

Thanks and best regards,
Guilherme.

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04-22-2014, 07:34 PM   #2
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QuoteOriginally posted by Guizo Quote
Hi,

Yesterday I tried my hand at two quite extreme high-key and low-key images: a marble sculpture shot against a white background and a black clay mask shot against a black background. This was my first attempt, so excuse my lack of expertise; I am posting the images to illustrate my question. I will formulate it as a high-key question, but I had the same problem with the low-key attempt (only backwards, of course).

The problem amounts to this: my white looks less white than I would like it to, and if I try to make it whiter, the histogram is clipped. Now, everything I read about high-key told me the steep spike to the right of the histogram would end quite abruptly, almost exactly in the lower right, as steeply as possible, as long as it was not clipped; however, if I post-produce the image to have a histogram that looks somewhat like this, I get highlight warnings, blown highlights and a clipped histogram. The only way I could get rid of all this was to use curves to bring all my whites to under 250 or thereabouts, but in this case my histogram will not fully reach to the right -- the spike will come down abruptly at the right, but there is still going to be a narrow, fully unused histogram space to the extreme right, since no pixel in the image goes above 250 (or thereabouts).

Same thing happened with low-key attempt: I had to bring all my blacks to above 5 (or thereabouts) so I wouldn't get shadow warnings, all-black shadows and a clipped histogram. To avoid this, my spike wouldn't start to the very left, but only after an empty unused space.

I have also seen video tutorials in which high-key portraits may be worked so as to have a fully blown-out, plain white background while retaining all details in the subject. This is not what happens in my high-key attempt: the first thing to blow out are the reflexes in the sculpture itself, and only then the background. All-black shadows in the low-key attempt also start in the chin of the mask and go up the middle line before any background shadows are clipped.

What am I doing wrong? Should I have illuminated the backgrounds differently? Maybe used a different post-production approach? Any help will be much appreciated.

Thanks and best regards,
Guilherme.
Based on the photos you posted, it looks like there's plenty of detail to work with. Try pushing the sliders a bit further, as even if you get an exposure warning in RAW oftentimes the final image will be fine.

I would also recommend increasing the contrast/clarity. You may have to do it selectively in the first shot because there's a lot more detail in the center of the sculpture than other parts.

I played with these pics in photoshop and I think I was able to make some nice changes, so if you're OK with my posting the edits, I'd be happy to upload them.

Adam
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04-22-2014, 08:10 PM   #3
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Really the true definition of high key and low key involves data loss in the respective areas. Doesn't have to be total data loss (i.e. completely blown or blocked up), but you should reach the point of diminishing returns. That is to say significant areas of the photo should be in the toe or the shoulder of the tone curve. To put it another way, if you're not clipping, you're being too conservative. Ignore what the internet tells you about what your histogram should look like and push it until you think you've got it. Then print it and assess, if it's too much, then back off a bit.

One other observation on your low key shot, I think it would be more effective if you kept the same exposure, but moved the light closer. This will do two things, it will give you brighter highlights, and deeper shadows due to the inverse square law. If you can get the light close enough, you might even increase the shutter speed to 1 sec or less to make your background even darker.
04-23-2014, 08:49 AM   #4
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Adam: Thanks a lot for your input. Please feel free to upload your edits -- I would like to see how these could be improved! Please comment a little bit on what you did when you post these as well.

Maxfield: Your comment makes things a bit more clear, so thanks for that. I just don't understand why, as Adam pointed out above, sometimes the PP software will show a highlight/shadow warning when actually there is no loss of detail. I am using SilkyPix before I learn how to use RAW Therapee, and I see at least for highlights there seems to be a gradation -- first a yellow tone starts blinking, and then a red tone, which I believe means complete detail loss. For the shadows, however, there doesn't seem to be any gradation -- either you do or you don't get a warning. But they start before the histogram hits the left, which is baffling to me.

Best regards,
Guilherme.

04-23-2014, 07:30 PM   #5
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Here are my edits:

New:
Name:  v2.jpg
Views: 437
Size:  89.0 KB
Original:


New:
Name:  v3.jpg
Views: 427
Size:  100.7 KB

Original:


Mainly I just boosted the contrast and made the first shot a bit brighter. Better results could surely be obtained through raw, i.e. a completely dark background in the second shot.

Adam
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04-24-2014, 02:49 AM   #6
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I believe your attacking high key and low key entirely from the wrong direction.


Traditionally with film both approaches are achievable in camera and this is what you have been trying to do in digital. I don't believe this is correct, it wont work well due to the restricted dynamic range of a digital sensor.


Its not the dynamic range itself that's the issue as much as how the sensor deals with extreme loss of detail, film falls away smoothly whereas sensors clip savagely. Also low key shadow areas generate excessive noise when underexposed in a digital camera.


This is my recommendation.


1 Expose as a normal image retaining details in all areas.


2 Use Post processing alone to entirely create high key or low key. All details will be preserved and you have maximum control over the look.


Adams work on your images is a clear example of how to post process, you avoided clipping that was absolutely the right thing to do and your images have contained the details to allow good post processing, I would simply expose more to the middle in both cases.


Start with the best well exposed detailed and noise free image you can, then work the magic in post
04-27-2014, 06:33 PM   #7
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Adam: Thanks a lot for taking the time to work on those. I particularly liked your approach to the low-key image -- it made it really stand out. As for the high-key picture, I had actually done something pretty similar to what you presented, but for some reason (probably the deeper shade) I thought that was too low-key for a high-key image. I see I was mistaken.

Imageman: I am not sure I have understood your comment. When you suggest that I "Expose as a normal image retaining detail in all areas", do you mean that I should expose it as a "normal high-key" image, tending heavily towards white while retaining detail in all areas, or are you suggesting I expose for a zero reading in my light meter and make it simply a correctly exposed image, leaving 100% of the high-key work to be done in PP? I would be very interested in knowing why you would suggest th latter approach for an intended high-key image, since everything I have been learning about photography points to a "get it as close as possible to what you want in-camera" approach. This is not to say I am disagreeing with your suggestion -- I am just a just novice who is genuinely interested in learning more about the whys and hows.

Best regards,
Guilherme.
04-28-2014, 08:00 PM   #8
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What I mean is expose normally in centre like any other image, then create high or low key entirely in post processing. Although if you prefer creating the look partially in camera there aren't really any major issues there, as long as you don't hit the dynamic range limit of the sensor.


Either approach is ok.


Its easy to slavishly follow rules such as "create the image in camera" and for composition and general lighting that's fine, but it is neither necessary or desirable in some cases. High and Low key images are such cases.


Film allows High and Low key to be created in camera, the latitude of the film stock creates subtle hues at extremes of exposure, with smooth graduated tonal fall-off as light levels reach extremes. The resulting images are a pleasure to view.


Not so with digital images. The sensor simply clips savagely when the image reaches extremes of the dynamic range of the sensor. The result is a an ugly posterisation effect with no subtle shading.


Deeply underexposed images suffer additionally from significant noise issues which film does not suffer from when exposing Low Key, Film generates deep dark shadows which are very pleasing, but sensors generate noisy shadow areas that are grotesque to my eyes.


The answer is to expose normally, making a well exposed image and then adjust in post processing.


Im not trying to convince you with argument here. Every sensor is different and you know what is acceptable to you in an image. What im suggesting is you take your equipment and try it, take 2 shots, the first a low key and make final adjustments in post, the second a normal exposure with all the adjustments to produce a Low Key image done in post. Then compare the two. Examine for noise in shadow areas. Use whichever method works best.


I expect with the in-camera Low Key, there will be significant noise issues. In the normal and entirely adjusted in post shot, there will be deep dark shadow areas similar to film.


Do the same with High Key.


Just because sensors should be able to render images well at extremes of exposure doesn't mean they will. sensors are poor at rendering in these difficult areas. Exploit the capabilities of your equipment and learn its shortcomings. And above all test different approaches on your equipment before deciding which to use.


Don't fall into the trap of simply using a method that should work best, find by experimentation the method that does work best.

---------- Post added 04-29-14 at 04:21 AM ----------

I should add two final comments.


In your original images:-


In the High key image I believe im seeing an area of clipped and blown out highlight, an ugly spot of overexposure on the sculpture. this appears to be the very clipping effect that sensors are prone to in High Key.


In the Low key shot I believe im seeing several areas of chroma noise, patches of magenta false colour typical of noise issues at deep underexposure that im highlighting as typical on sensors in Low Key.


Examine the original images and see if they are present there.


If they are I believe they would have been avoided entirely by following my approach to correct normal exposure and then post processing for High and Low key image making.

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