It can be hard to nail down highlights - they look good on screen then print muddy. it’s all relative. On screen highlights are judged next to the darker parts of the image, while on paper, they are compared to the white of the paper border. The result is often either muddy highlights or making a lot of reprints.

It’s handy to be able to see just exactly where your highlights are in the image. The histogram is of some help but can’t tell you how close to white a particular part of the image is. Using LightZone would be one way to solve the problem but I prefer to edit my images ‘freehand’ rather than making print area selections so that isn’t an option for me.

Here’s what I do

In Photoshop, create a new action (using the little triangle at the top right of the actions palette). Name it Highlights 250 (trust me on this one). Now that you are recording, go down to the layers palette and select threshold and when it comes up, set the threshold to 250. Now set the layer opacity slider (top right in the layers palette) to about 85%. next double click on the name of the new layer you just added and change it to Highlight 250. Go back to the actions palette menu and ‘stop recording’.

Note by the editor: I learned this invaluable technique from George but use an opacity of 50% (matter of taste).

What you have done is to create a top layer which shows the underneath image as a very dark version of itself (only 15% showing through). You have arranged so that the threshold layer shows bright only those tones in the image which have an 8 bit density level of 250 out of 255 (0 is black, 255 pure white).
How you use this is in two ways.

You can judge your highlights as they are now - if none of them show up bright, then it means that nowhere in your image do you have any tones brighter than 250 so your print will have absolutely no pure white. That might be what you wanted, but perhaps not. More likely you wanted some highlights to approach pure white but just kiss it, not overwhelm it.

Picture before dodge/burn

Threshold view of the above picture

What you can now do is either dodge the underneath image or create a new layer to fit between the image layer(s) and the threshold layer just created which lightens the highlights. It could be a curves or levels layer or even a blending layer of some type (I prefer using dodge highlights on a copy of the original image as a separate layer so I can always tone down the dodging by using a mask).

Note that my strong preference is to do general image editing with masked curves layers working in the mask and only do dodging and burning as the very last step to fine tune the image so I’m using this threshold layer trick after most of the image editing has been done.

I now ‘stroke’ my highlight areas in the copied image layer with my mouse until they just break through the 250 barrier and show up as bright on screen. It’s possible to really make an image ‘pop’ this way. I have taken images photographed in completely flat light and added highlights to rock edges, corners, etc.

Picture after dodge/burn

Threshold view of the above picture

I will turn off the threshold layer intermittently to see how the image is coming, but don’t be too surprised if your highlights look too bright on screen - test the effect by making a print. When finished with the dodging, I simply turn off the threshold layer with it’s check box to the left in the layers palette and flatten the image.

You can modify this action to suit your printing style. You might find that a value different from 250 is needed - perhaps with your printer 250 is already printed as pure white and you’d be better with a lower number. Perhaps your printer is really good at printing subtle highlights and can differentiate 250 from 255 pure white quite easily in which case you might select 253 for your cutoff.

If you’d prefer more of the underlying image to show through to make seeing where to dodge easier, then change that opacity slider to a lower percentage.

You can make a similar action for shadows in which the whole image will be pale gray and the dark shadows showing their real darkness. In this case, I set the level somewhere around 10 to 20 depending on the printer and paper I’m using.

As a final trick, make a keyboard shortcut for the action so a single keystroke will enable it.