Jump to content

Tutorial: Colour correction using Curves in PSCS2


andybarton

Recommended Posts

Advertisement (gone after registration)

There was a post yesterday Moose Skull in Boreal Forest whereby a question was asked about setting black white and grey points in an image using the eye-dropper.

 

I said that there was an excellent tutorial on same at photoshoptv.com podcast Episode 17. I take the liberty of explaining this technique here, for those of you who either don't want to download the podcast or whatever. So, thanks to the Photoshoptv.com guys - long may your iTunes podcasts be free :)

 

1 Open your image that you wish to colour correct, and set the levels if necessary.

2 Open up the Curves Adjustment pallette and double click on the Black Eye-dropper. Set the r/g/b numbers to 10 in each box.

3 Double click the White Eye-dropper and set the r/g/b numbers to 245

4. Close the Curves box and click Yes when prompted to Save the new settings as default (You only have to do this bit once)

5. Open a new Threshold Adjustment Layer from the Layers window or via the menu. The image will temporarily change to all black and all white.

6. Move the slider to the extreme left, so that the Threshold level number gets down to 1. If you image does not have any pixels at that low level, you may need to go back up to level three or four or even more. You will be able to see the pixels at these values in the image window.

7. When you have found the lowest number pixel, you need to hover your cursor over the image window. You will notice that it changes to an Eye-dropper again. Go to a pixel that has the lowest setting and holding down the shift key click on this black pixel.

8 Now, do the same at the other end of the threshold scale, shift-clicking on the whitest pixel. Close the threshold dialog box and delete these new Adjustment layers that you have created.

9 Now, you need to create a new layer, which is 50 % grey, in order to set the grey-est point. So, use the new layer button on the layers window or Shift-Command/Control-N. Then, fill this with 50% grey. I use Shift-fn-F5 on my PowerBook, so I suspect that Shift-F5 will do it on a desktop. The fill contents needs to be set to the 50% grey.

10 Change the layer blending mode to "Difference" using the drop down control on the layer window. You will now see the image has changed again - temporarily.

11 Add a Threshold layer to this one, as you did before, and slide the slider down to the extreme left. This will then show you the pixels that are the grey-est. Once again, Shift click the Eye-dropper cursor on this pixel.

 

Nearly there, now :)

 

12 Close the dialog again and delete all these new layers, which will leave you with your original image and three "target" points, numbered 1,2,3

13 Open a new Curves Adjustment layer.

14 With the CAPS Lock key depressed click on the Black Eye-dropper in the Curves adjustment box and hover your cursor over point 1 in your image. When it is exactly in register, click on it. Do the same for the white point, number 2 and the grey point number 3.

15 Close the dialog box.

 

Your image will now have the black, white and grey points set to their blackest, whitest and greyest and any colour cast should have disappeared.

 

This may look long winded, but, after a couple of goes, it becomes very quick and easy. You can, of course, record Actions to do a lot of this intermediate step work automatically.

 

I have shown a "Before" and "After" comparison here.

 

PM me if you need any further explanation and if I've forgotten a step, I apologise. This is becoming second nature now.

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

Link to post
Share on other sites

Here's an example that I did, while recording the above as an Action. I managed to get all the above procedure, apart from the final curves adjustment layer part into one Action. Dead easy.

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

Link to post
Share on other sites

Andy,

 

thanks, good stuff!

Now waiting for a rainy weekend to study in detail.

Just did a hush-hush correction following your method and yes, this definitely increases picture quality. It seems only minor but it is the important tiny bit.

Unfortunately there are tons of possibilities to do corrections and I need to find out what to use for what circumstances.

With the complexity of PS you can spend months or so, I am afraid (my book staple on PS meanwhile has reached half a meter or so). So I am always grateful if I see another quick run-script to use for a first impression...

 

best - Klaus

Link to post
Share on other sites

Thanks for this step-by-step instruction, Andy!

 

It's always useful to have another tool for color correction.

 

Steve Unsworth's recommendation of iCorrect EditLab Pro some time ago led me to a purchase of that plug-in as well, with which I have been happy.

 

Thanks.

 

Allan

Link to post
Share on other sites

Hi-

 

Interesting procedure and not bad to follow after a try or two. I too changed my defaults on the curves about a year ago using 12 and 245. This was the preference of the particular author of the procedure.

 

Without conducting all sorts of tests, anyone know offhand what differences may be seen at 10 or 12 on the black? I tend to think it's a hair splitter.

 

Best,

Link to post
Share on other sites

Advertisement (gone after registration)

Andy, thanks a lot.

 

I was looking for a simple solution for color cast: there it is.

 

Tried it, it works fine.

 

I will investigate the Photoshoptv.com site further.

One never knows too much about Photoshop.

 

Thanks again.

Link to post
Share on other sites

Hi-

 

Interesting procedure and not bad to follow after a try or two. I too changed my defaults on the curves about a year ago using 12 and 245. This was the preference of the particular author of the procedure.

 

Without conducting all sorts of tests, anyone know offhand what differences may be seen at 10 or 12 on the black? I tend to think it's a hair splitter.

 

Best,

 

 

I wouldn't think that you could tell the difference between setting the default Black to 10 or 12

 

Clipping the range down like this gives better results on inkjet printers, apparently.

 

I know that there are some excellent plug-ins out there, but this is free and there's always something more satisfying about doing it yourself.

Link to post
Share on other sites

fot those who would like to check the tonal b/w range ability of their respective printer I recommend to visit

 

http://www.outbackphoto.com/booklets/resources/fap/

 

and load the file "PrinterRamp.tif"

 

Performing the test print procedure tells you exactly what you can get on a specific paper. A difference in the start value of 10 or 12 might be visible; although this for sure is for perfectionists only...

 

Have fun - Klaus

Link to post
Share on other sites

Andy, thanks a lot.

 

I was looking for a simple solution for color cast: there it is.

 

Tried it, it works fine.

 

I will investigate the Photoshoptv.com site further.

One never knows too much about Photoshop.

 

Thanks again.

 

 

Daniel - if you want the videos for free, access them via iTunes, which is also free. If you d/l them directly from the photoshoptv.com website, they are $1.99

Link to post
Share on other sites

I guess it's true that you can't teach old dogs new tricks! I find the details in this tutorial absolutely stupefying. To me, none of it is intuitive. I pray that film remains available forever because all the trappings of digital photography drive me nuts. My MP and a roll of film are all I need for Nirvana! Best regards, Bill

Link to post
Share on other sites

Bill-

 

I know what you mean; digital does seem to make everything more complicated, slower, less soul-ful and more equipment intensive (which is ever changing) than an M w/TriX/Rodinal (my choice anyway) and a good darkroom.

 

But... it is what the future brings and has its merits. Perhaps we are the pioneers as in the late 1800's.

 

Let us not forget the (or might I say our) roots and continue to embrace and understand this new technology while not being taking in by its ever changing hype from the software and hardware folks. Perhaps the M8 will allow the true picture maker to control the camera without an LCD screen and various button sequencing. (BTW, it appears out of my league)

 

Perhaps the final version of LightRoom will be the beginning true photograper's tool which does for digital what the darkroom does for conventional. Perhaps then the same computer will serve us as long as a quality enlarger/lens combination or local quality lab does or once did. It is then we all can go back to concentrating more on the images we make and process rather than second guessing what release is just a show away.

 

I recently mentioned in an Olympus forum, my M-6's from the late 80's will return approx 60% of the original cost. Can I say that about my 5050 or E1 or any other digital capture device just a few years later? What is the true cost vs true value of digital? Pioneers we are.

 

Best,

Link to post
Share on other sites

I guess it's true that you can't teach old dogs new tricks! I find the details in this tutorial absolutely stupefying. To me, none of it is intuitive. I pray that film remains available forever because all the trappings of digital photography drive me nuts. My MP and a roll of film are all I need for Nirvana! Best regards, Bill

 

Bill

 

I never said it's intuitive, which is why you need to see wither the video or to have it written down. It literally takes a minute to do once you have done it a couple of times - even less when you record an action to do all the standard stuff.

 

I have never used it on a digitally produced image (because I don't have any), only on scanned film. Unfortunately, no one has managed to find a way of getting images off film and onto a screen without scanning thus far! ;)

Link to post
Share on other sites

John J., your points are well taken, thanks for the kind reply. Andy B., I've been very lucky so far. Most of my scanned negatives render presentable prints and screen images without my having to drag them throught the "digital jungle" of Adobe or some other counterintuitive software. If the time comes when I can no longer get good results the easy way, I'll chuck the scanner and computer onto the front lawn and slink back into the darkroom. My ossified 70 something years old brain cannot tolerate much more of those daunting software programs which seem to obsolete themselves every few months! Best regards, to all., Bill

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...