Setting Black and White Point Values in Levels or Curves

[vijo]

Hi,

I'm in the process of learning how to use the Levels and Curves feature in Photoshop. Levels and Curves two features which I’m learning for image correction. As I’m learning these tools I’m having a problem with a concept in Levels and Curves. From my reading on the subject and as applied to correcting the flaws in images the problem I’m having is with the concept of the "Black and White Point Values". I read that when setting the Black and White Point from your image one is to find the darkest and lightest areas with the eyedropper tool as per either what tool you are using, that is Levels or Curves. To see the values of the darkest point (setting Black Point) and the values of the lightest point (setting White Point) we must use the data from the Info Palette. Therefore my question is in setting the Black Point with the eyedropper tool, in the Info Palette I’m to find the darkest point in the image, that's fine BUT how do I know what the darkest point in the image is, that is I know what dark colors are but on the info palette how is this interpreted, do I look at the RGB values or the CMYK values or both, and for the darkest area for the Black Point value is it a high or low number in the RGB or the CMYK data or both that I’m to choose. Likewise the same holds true for setting the White Point Value, but I would need to know what values I’m I looking for in the Info Palette, that is a high value or a low value.

Thanks.

[BdubYA]

I can answer this! heh....DO a THRESHOLD on the image, slide the bar all the way to the left and most of the image goes white except for a couple of black spots/pixels. This grouping of black should represent the darkest point in the image. Now do vice versa going right and image turns mostly black showing groupings of white spots/pixels. This represents the lightest part of the image. So you have Black and White, now you need gray. Get out of threshold, by clicking on the eye to hide it. I was taught that you want the RGB values to all be closest to 130, which should represent pure gray. It doesn't have to be perfect because I NEVER find pure gray. So as close as you can. Now using curves you can color adjust the image! I hope my explanation wasn't too complicated. Although im no expert feel free to message me if you need help with it.
BdubYA

[Chris49]

hay Vijo, easy money, go to Image> Adjustments > Threshold

To set your black point drag the slider all the way to the left, Then slowly drag to the right until you can see some black appear, Now hold the Shift key and left mouse click that black spot

Now for the white point

To set your white point drag the slider all the way to the Right, Then slowly drag to the left until you can see some white appear, Now hold the Shift key and left mouse click that white spot

now exit out of the Threshold adjustment menu (Press Cancel NOT ok)

go into your curves dialog box, as you can see where you clicked there are now markers for your white and black points. now use The white and black "Set Point Tools" on these markers and your done

Like I said easy money :)

[vijo]

Thanks for the info guys.
I never saw this aspect being taught this way.
I'm not at my computer/photoshop at the moment therefore when I try your method i'll let you know the outcome.

Thanks.

[vijo]

We'll I tried the above-mentioned technique and let me tell you that this is amazing, I never learned this in school or for that matter in any book, we'll I know where to turn to next time I have a question, thanks Chris49, BdubYA and pixeladdiction!

In closing I'll be going more indepth with this technique therefore I'll post further comments if I
discover more.

Once again thanks.

[jachang]

This looked like it would be a tremendous help. However, when I tried it, it didn't work for me. I'm doing something wrong. Everything went fine until I entered the curves box. I clicked with the black eyedropper on point number 1, and that improved the picture. Then I clicked with the white eyedropper on point number 2, and the whole picture got a really blue cast over it. What am I doing wrong? Thanks for any help! :)

[Chris49]

If you post the picture your working on Jachang I'll see what I can figure out. :)