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Novice Corner - Setting White & Black pt
Diff
Registered Users Posts: 107 Major grins
Question: How do you set the "white" and "black" point in a photo when there's not a white/black point?
Question: Is it necessary to do this with every image?
This is open to anyone. jjbong provided me some feedback on an image I posted in thePop Tutorial – New & Improved series. I was at a lost on how to set the white & black point when there’s no clear “white” (or black) pt in an image?
This a follow-up question to get some clarification regarding a new photo.
jjbong stated this…
[FONT="]>> Here's a way to do it with curves. The key is understanding what you want the "white point" to be in this picture. In David's tutorial, it's 247, 247, 247, or pretty much pure white. Here [Ref - My photo in Pop Tutorial] it obviously isn't. Using the Thresholds command described in the tutorial, the brightest point of interest is yellow in the flower. So you want the "white point" to be as bright a yellow as you can get. This means B=0 for sure. This particular yellow (Ref – My photo in Pop Tutorial] looks a little on the orange side, so we probably want R=247, and the only question is what G should be. I experimented until I liked what I saw (G=231). For the black point, it's easy, as the bee's body is the darkest spot and is indeed black. So we're aiming for R=G=B=5, or thereabouts…
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Question: Is it necessary to do this with every image?
This is open to anyone. jjbong provided me some feedback on an image I posted in thePop Tutorial – New & Improved series. I was at a lost on how to set the white & black point when there’s no clear “white” (or black) pt in an image?
This a follow-up question to get some clarification regarding a new photo.
jjbong stated this…
[FONT="]>> Here's a way to do it with curves. The key is understanding what you want the "white point" to be in this picture. In David's tutorial, it's 247, 247, 247, or pretty much pure white. Here [Ref - My photo in Pop Tutorial] it obviously isn't. Using the Thresholds command described in the tutorial, the brightest point of interest is yellow in the flower. So you want the "white point" to be as bright a yellow as you can get. This means B=0 for sure. This particular yellow (Ref – My photo in Pop Tutorial] looks a little on the orange side, so we probably want R=247, and the only question is what G should be. I experimented until I liked what I saw (G=231). For the black point, it's easy, as the bee's body is the darkest spot and is indeed black. So we're aiming for R=G=B=5, or thereabouts…
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~ Diff ~
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Next, you can view the clipping of each channel individually which indicates if there's saturation clipping by using the alt/option key in a few places. In Lightroom or ACR, that's done by alt/option clicking on the Exposure and Black sliders. There may not be a real white (there often is a real black) and the overlay you see indicates this. A color indicates one channel clipping, white indicates a white clip (all channels are 255/255/255 or 100% depending on the application), black would be 0/0/0. You can do this after the fact, with far less control and quality in Photoshop by using the same key command in both Curves and Levels (in levels its the keys held down while clicking on the white and black Input Sliders).
Author "Color Management for Photographers"
http://www.digitaldog.net/
For an image that contains these two endpoints, one would have to first decide if the image actually required forcing the darker values to a darker/neutral value and whether forcing the lighter values lighter/neutral was appropriate.
For an image where there is no "true" white/black point, then forcing the image to be neutral at the endpoints may not be what is required or desired. The question then becomes, do I make the darker tone darker (but not neutral) and the lighter tones lighter (but not neutral), so as to preserve colour balance while increasing tonal contrast.
One can use the colour samplers and info palette set to say Lab or HSB readings to make this process a little easier, as does blending the curve in Luminosity blend mode if one does not wish to introduce hue shifts.
More detail on the basic process of setting dynamic range and adjusting colour balance via curves can be found here:
http://www.ledet.com/margulis/PP7_Ch02_ByTheNumbers.pdf
http://www.eddietapp.com/PDFs/ccmethod_cs.pdf
http://www.adobeevangelists.com/pdfs/photoshop/tipsandtricks/CorrectByNumbers.pdf
"Question: Is it necessary to do this with every image?"
Depends on the image, although many images can be improved by extending their tonal range, although some images should be "flat" and not using a fuller range of tones from near black to near white. Whether or not extending the tonal range should adjust the colour balance or saturation of the image is very much an image dependent and or personal decision.
I presume that these questions relate to Photoshop and rendered data, rather than raw camera data and a raw processor. Most raw processors set the range, but do not adjust the endpoints to be neutral, as in the case of ACR/ALR exposure and black point sliders, which set tonal range but not colour balance.
Hope this helps,
Stephen Marsh
http://members.ozemail.com.au/~binaryfx/
http://members.ozemail.com.au/~binaryfx/
http://prepression.blogspot.com/
Thank you for sharing & yes, it does help!
I came across an article by Frazer that I believe came from Creative Pro site (?) "Correcting color images in Adobe Photoshop, using Curves, Color Range selection, Hue/Saturation Adjustment Layers, and more."
I'm wondering if what he putsforth in the article is parellel to what you both are stating?
Frazer - "I'm often asked, "what's the easiest way to color-correct images?" My answer is always the same: Fix the neutrals and the rest will follow. True, it isn't always quite that simple -- fixing the neutral areas won't always solve your color problems. But surprisingly often, if you find something in the image that you know should be neutral -- that is, white, black, or gray -- and you make it so, you'll find that the rest of the color falls into place."
Frazer - " [FONT="]In Adobe Photoshop, the tools I always use to accomplish this end are Curves, the Info palette, and a Photoshop working color space. It may seem odd to include the working space as one of the tools, but there's a very good reason for doing so. Photoshop working spaces are inherently gray-balanced, which simply means that equal numbers of R, G, and B will produce some shade of neutral gray, black, or white."[/FONT]
[FONT="]Frazer - "[/FONT][FONT="]I use the Info palette to determine pixel values. The Info palette always reads the pixel values of the pixel or pixels beneath the cursor. The exact values that appear depend on two things: the zoom percentage you use to view the image, and the setting for the eyedropper tool. This latter affects the numbers that appear on the Info palette no matter which tool you're using. I always set it to Point Sample -- which takes color data from a specific pixel -- rather than 3x3 Average or 5x5 average which grabs the average values of a grid of pixels. The downside of Point sample is that you need to be careful that the pixel you pinpoint is representative of the image.."[/FONT]
[FONT="]Oh, Stephen...[/FONT]
http://www.adobeevangelists.com/pdfs...tByNumbers.pdf
Has changed to: http://www.jkost.com/photoshop.html
I've not located the specific article yet.
This is similar to your other image, in that the bright point is yellow. Using the method described in DavidTO's tutorial, you can find the bright and dark spots using the Thresholds command:
Color sampler 1 is at the bright spot and sampler 2 is at the dark spot. Thresholds is a pretty course tool, and I find it useful to go over the area I've identified as bright or dark, looking at the Info palate, to get the best point possible (with Lab displays, you're looking for the highest and lowest L values for lightest and darkest points).
In this, as in your earlier shot, the bright spot is yellow, not white, although this looks to me much less orange than the previous. So again, you're looking for B=0 at the brightest spot (really bright yellow) and R very high (at least 245). And again, the question is how much G you want. I set R at 252 and G at 237 using curves, as it looked reasonable to me, but I wasn't there and I don't know what you're trying to bring out. You can just play with it to see what makes you happy. You have to be careful with the G curve so as not to lose the orangeness in the middle of the flower, which is the reason for the other point on the G curve. For the dark spot, R=G=B=5 was my target. Although the dark spot isn't black, but a really dark brown, we can't discriminate colors very well at that end of RGB, so it's generally safe to set it to black. Anyway, here are the curves I used:
with this result (original on left)
This isn't finished - it's just the basic step of getting the most dynamic range. If you use this technique, you have to decide how much bright yellow you want on the flower tips, and modify the G curve to taste.
One last comment. This image wasn't terribly far off to begin with, so the differences after this step are somewhat subtle. When you take the next step, which is to steepen the original curves in the R, G, and B to make the steepest parts of the curve where the flower is, you get something noticeably different:
Again, this isn't science (although there are principles to it). You need to play with the curves to get the thing you want out of it.
Which isn't at all an issue. Plus, if indeed you clip to black and white, by that very definition, those two extremes can be (but don't necessarily should be) neutral. 0 or 100% (using LR scale) is neutral. The rest of the image? Well that's another story.
And in Photoshop, using rendered data, 0/255 is neutral, the rest of the image? Maybe, maybe not. Lastly, it might be useful to define when and why the range should be set at the Raw stage, not the rendered stage.
Author "Color Management for Photographers"
http://www.digitaldog.net/
In most cases, yes! Even images that have a desired color cast (sunset imagery as an example). So there are two things going on here: Neutrality of the two extremes and the tonal scale you set by getting just shy of clipping (because sharpening and conversion to the output color space may, may take you over).
Note, this is TOTALY subjective too. Look at the work of the great photographer Greg Gorman. You'll see a huge amount of shadow detail clipping to black. That's his style. There's nothing that says you have to show detail there.
Author "Color Management for Photographers"
http://www.digitaldog.net/
Thanks for for your support...
~ Best ~
I'm I headed in the right direction with what I'm posting & the questions I'm raising?
One suggestion. You've got pointers to a number of web sites and several books, and you've found some things that resonate with you. You mentioned practicing these techniques on some pictures. I'd suggest practicing on a lot of pictures, especially pictures that are wildly different. This does two things. It hones your skills, in both your eye and your hand. You'll see things that are out-of-whack more quickly, and your post-processing skills will become more solid. The second thing is that many recommended techniques work for some kinds of shots, but not for others. You generally don't get caveats in the articles describing these, and you have to find out on your own.
I always save my original raw files, for a number of reasons. One is that as I learn new techniques, I can go back and compare results to the best I could do at that point in time with the techniques I knew and the workflow I had.
I hope this is useful.
I'm going to stepback for a number of days, taken in what everyone has shared, and begin practicing on various images.
Thank!
Not looking for an argument, simply noting that the black and white point tools (or curves for that matter) in some raw converters are not doing the same thing as global, individual channel curves in Photoshop, as happens when one sets a neutral shadow/highlight on an original that does not have neutral tones in the regions being set for range/balance. As I previously stated:
The other day I was scanning a photo of a mosaic mural for an artist client. The mural was done in large, hand painted ceramic tiles. Earthy colours, but the image was not overly saturated and was meant to be a little flat in range. After scanning and setting conservative endpoints in the scanner, the file was brought into Photoshop for fine tuning. The endpoint curves that I applied to the image in normal blend mode produced too much saturation and hue shift. Blending the curves in luminosity mode was the answer in this case. If this was raw camera data and not a scan, the rendering approach would have been different to get to the same desired final image.
In order to use the various tools to best effect, it is helpful to understand what they are doing. Raw camera data and the tools in raw converters often do things in a different way to more traditional methods such as working with scans in Photoshop.
Stephen Marsh
http://members.ozemail.com.au/~binaryfx/
http://members.ozemail.com.au/~binaryfx/
http://prepression.blogspot.com/
The practical implications for the end user being what?
There's a whole lot of stuff going on in a Raw converter that's totally different then Photoshop such as, its happening in a linear encoded space, its happening from scene referred data, its happening based on metadata instructions, its totally non destructive, its really, really fast (because you're not altering a huge pile of baked pixels). IOW, they are different, and there are mostly only advantages to doing this from the Raw data in a converter, something we could go into if others so desire.
But your original point doesn't discuss anything other than they are different, so why is this important in terms of clipping? What's so special or useful (or not useful) about global, individual channel curves as far as an end user wishing to produce a desired color appearance?
They sure do. And depending on the scanner software, its a lot different there versus doing the work in Photoshop. If this were 1995, we could discuss the advantages and disadvantages of doing this in say ColorQuartet on a ScanMate versus Photoshop 4, but I suspect its not a useful discussion these days. Now Raw rendering and Photoshop color correction? There's a big difference that is pertinent to most users.
Author "Color Management for Photographers"
http://www.digitaldog.net/
My head is spinning with this discussion at your level of context.
Is there something here for me ("us"), the novice, to understand? Remember, shooting RAW is down the road.
Thanks!
Diff, the way I personally see it, if you are working on in-camera JPEG/TIFF rendered files, then discussion of processing or rendering raw camera data would be best for another day and a different thread, as the final file that you are using is not a raw camera file.
With later versions of Adobe Camera Raw, one can edit non raw files (edit, as opposed to render)...then discussion of using these tools would perhaps offer something to you.
As I have been attempting to make clear in my posts, setting the black and white point in Photoshop often means forcing global levels/curves onto the image, differently in each channel, affecting colour balance and saturation. This could be done manually with the aid of fixed colour samplers and the info palette, or with the use of the set white/black/gray point eyedroppers in levels/curves. Further to manual levels or curves, Adobe offer 3 different auto methods plus a neutral midtone snap option for an auto level/curve, additionally one can also blend a manual or auto level or curve in luminosity mode or use other techniques.
The previous links should be a good place for you to start, as often happens, once the initial question has been answered, a thread will sidetrack onto other areas.
Sincerely,
Stephen Marsh
http://members.ozemail.com.au/~binaryfx/
http://members.ozemail.com.au/~binaryfx/
http://prepression.blogspot.com/
I think that road will get quite short after you read this:
http://tinyurl.com/33msxz
Render, then you don't have to worry about "color correcting" because there's nothing to correct.
Author "Color Management for Photographers"
http://www.digitaldog.net/
[FONT="]I'm left being very curious with your reading reference & commenton how I'll be left, after reading it. So, I'll read it tomorrow and get back with how it left me.
~ Diff ~
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