RGB Values; 3 & 252

[FrankG]

How best to achieve this (instructions from a stock agency):

RGB Values
RGB values should be limited with a black point of no less than 3 and white point of no more than 252. This
should be performed at the end of Photoshop editing. In doing this, extreme highlight and shadow detail will
retain all the information needed to print successfully. This also will limit the possibility of color banding and
clipping within the file.

Do I create a Curves adjustment layer and drag the top & bottom points to 3 & 252, or is there a better way to achieve the task?

Thanks,

Frank

[digitaldog]

These guys are kind of clueless! What they are trying to tell you is not to have a white pixel value that is RGB255, 254, 253 (clipping) or Black 0-3. But since they don’t tell you what color space, the numbers are a bit meaningless! That is, if the data started out as ProPhoto RGB with 3/3/3 but they wanted sRGB, it would end up as 1/1/1 (wrong according to them).

But to answer your question, I’d do this in Levels. Just set the OUTPUT level field to the values you wish.

[Ed Foster, Jr.]

Frank,

I was writing this at the same time Andrew was posting and his answer is right on. But here is the method for doing it in levels that I wrote previously.

You could easily do this with Levels (Command L or Image>Adjustments>Levels) or by using a Levels Adjustment Layer. Open your Level window and double click on the white eyedropper and then set each of the R, G and B values to 252. Double click on the black eyedropper and set each of the R, G and B values to 3. Then, using the white eyedropper, locate the brightest white value and click. Do the same with the black eyedropper on the darkest black value.

Typically for offset reproduction, they are trying to keep from blocking up the shadows and also retain a dot in the white areas.  However, I would think that the end user would set these points based upon their specific reproduction requirements, but that's another issue.

I hope this helps.
Ed

[bill t.]

You can also use a Threshold layer to see if you have any significant numbers offending pixels to start with.

For real digital stock agencies stuff like that would normally be part of a standard, in-house image normalization system, which these guys maybe don't have.  Yes, for better or for worse, many agencies will mess with your images so they present "in a balanced manner" in the galleries and are "fully publication ready."  Get used to it.  It's the next best thing to homogenized milk, and a kind of visual toilet seat cover for the brave new publishing world.

[FrankG]

Why use the droppers to bring up the color box and fill in each of RGB when you can just enter the output numbers in the levels box ?

Also, it can, in some images, be a little difficult to visually (eyeballing) pinpoint the very darkest or lightest tones to click on

[FrankG]

When using a Threshold layer , you can see the lightest & darkest values by moving the slider slowly off each end, but how do you mark them so you can see the points on the image under the layer ?

[bill t.]

I bet there's a slicker way to do this, but you can use the old selection tool with "Contiguous" not clicked and a low tolerance number to get a selection on the white or dark areas of the threshold image, then convert that to a utility mask for later reference.

But the basic use I have for Threshold is simply to identify when my darkest and lightest areas are falling into certain ranges and in what predominance, and in particular what parts of the dark areas are falling below the densities my media can represent well.

And while you are looking at the threshold image, you can manipulate other control layers like Levels to see what's happening.  So you could set the Threshold slider to say 252, then manipulate Levels or Output Ranges on layers underneath until you don't see any more white areas.

[Schewe]

How best to achieve this (instructions from a stock agency):

RGB Values
RGB values should be limited with a black point of no less than 3 and white point of no more than 252. This
should be performed at the end of Photoshop editing. In doing this, extreme highlight and shadow detail will
retain all the information needed to print successfully. This also will limit the possibility of color banding and
clipping within the file.

Frank,

You gotta really ask if the stock agency is on drugs...

If they are referring to "usable detail" that is one thing, but to artificially limit specular highlights to 252, they are wrong. Purely wrong. What that will do is guarantee that what should be a pure paper white ends up with a scum dot–which is not optimal. Are they asking for RGB files (what color space?) or CMYK? If RGB, what color space (note, the odds are REAL good you won't to offer either sRGB_if they are real stupid–or Adobe RGB if the ere sightly less stooopid (not likely).

It is YOUR job to know EXACTLY what you should be submitting...you really should not depend in idiots...(seriously, that will get you in hot water).

[FrankG]

They're asking for 8bit RGB & do not prescribe a color space but rather suggest leaving it it in the col space I work in (Adobe_RGB_1998).
I agree with you on the specular highlights being left to 'go over..' or the image will look 'flat'.
Assuming the scene doesn't contain any speculars, shall I just enter 3 & 252 in a Levels output box ?

[pfigen]

As I replied in your similar thread at another forum, simply entering those numbers will not have the desired effect unless your end points are 0 an 255. If your black is at something typical like 6,5,7, setting the output slider to 3, will change the number to 9,8,10. Same thing happens on the highlight end but in the opposite direction. The advice to use output sliders is outdated and redundant if you've already set your endpoints with better, more accurate methods. I would prep the files the way I know how to do them best and submit them, not worrying about the fact they the stock agency is out of touch. My guess is that no one will notice and your files will look better than anyone who actually took their advice.

[digitaldog]

Peter raises a valid point about using the updated values on image that themselves fall outside a 0/255 range. You would not want to update the values as he points out, the newer values would be way too ‘flat’. But such images should not be edited anyway, at least if we are to follow the silly suggestion of the stock agent. When you go into Levels, it should be obvious if the values need to be altered from 0/255 to differing values using the input fields. I should have pointed this out. But my larger point was, just send the images as you have them.

[MarkM]

Trying to fix these problems with levels is silly. The agency wants to avoid clipped highlights and shadows. If you are starting with a clipped image and adjust the output levels slider (or any thing else in PS) you still have clipping—it's just that you lose detail at 252 instead of 255. You haven't gained anything.

A better approach is to:
1. Make a good exposure.
2. Set the white point and black point to the desired values when processing the RAW file.

[Alan Klein]

How do agencies, photo magazines, etc handle photos they like but require Photoshopping?  Do they expect you to do this?  Or will they use their experts to work on your RAW image?

[pfigen]

Alan - As a commercial photographer, I have to work on more than my share of stock images of all types for various clients and from a variety of stock houses. Obviously, I haven't seen images from all the different agencies, but quite a few, and I'd have to say that it's rare when I come across and image I can use as is. I'd rather get a slightly conservative image that's easier for me to mold to what I need, but so much of what I see needs basic tone control - setting endpoints, fixing color casts, local contrast enhancing, dodging and burning, not to mention dust spots from dirty sensors. The stock images I see from film uniformly suffer from substandard scans, but then, my standards for film scans are very very high.  I don't think that most agencies do much work on the images themselves. As far as I can tell, they rely on the contributing photographer to be competent enough to provide an image as they see fit.

[FrankG]

Mark,
Please describe how to do you do this in ACR (Camera Raw 5.3.0.21) ?

Does the Exposure slider represent 'white point' and the Blacks slider represent 'black point' ?

From what I can see, the Blacks will start clipping if you move off the left hand side of the slider