"White Levels" in Photoshop or LR

[Kamiha]

Hey, I need some help!

I just started working for a photographer editing photos. She is sending photos out to be printed in a magazine and is asking me to give her a number between 1-100 for the "white levels". I have no idea what she means. She says that she doesn't know how to use photoshop but knows that, "the whites can be no more than 100 or they lose detail". (?) I use the level and curves layers in Photoshop to ensure the photos are not over/under exposed, but that doesn't give me a number between 1-100. She wants an exact number and a scientific way to show that the whites and blacks are not over/under exposed.

What is she talking about?

Please help! Any information on this is appreciated - I don't know what to tell her and she thinks I'm an idiot for not knowing :/

 

[KmH]

The scale is 0-255. So, who knows where the photographer is getting 100 from.

Whites, also known as highlights, start losing detail at 250. By 255 there is no detail left. Whites at 255 that have no detail are often called 'blown out'.

Some qualification is needed, because in Photoshop 'white' is actually 3 colors added together - red, green, blue (RGB). Consequently all 3 color channels may not be at 255.
If only 2 channels are at 255, some detail in the whites can be recovered using ACR (Camera Raw). If only 1 channel is at 255 more detail can be recovered with ACR.

In ACR wherever you hover your cursor, ACR will show the 3 RGB color channel values for that point in the image under the lower left corner of the Histogram that is displayed on the right side of the workspace. Or you can use the ACR Color Sampler Tool and sample several points in an image.

In Photoshop you can open the Info window, hover your cursor, and see the color channel values. Photoshop also has a Color Sampler Tool. Note: You can also set how many pixels get sampled. There are 7 sample size choices that range from just a point sample to a 101 by 101 pixel sample that averages the color channel values in the square.

ACR and Photoshop screen shots:

Photoshop Info window:

 

[The_Traveler]

what you could do, easily, is open the info window and choose the eyedropper tool.
Click on a white area and record the values for the rgb.
Repeat with black.

then report those to her with a brief explanation.