Im working my way through Katrin Eismann's superb book on Restoration and Retouching. Periodically you are told to add a curves adjustment, layer and click on OK without making any adjustments.
I dont quite get why this is or what it achieves. Can someone explain please?
Ali W

Does she follow it by asking you to Change the mode of the Adjustment layer to Multiply or Screen? The attached file has the same effect as changing the mode of your empty adjustment to Multiply.

This is the kind of thing that you learn through experimentation. I'm not sure where you are looking in the book, but depending on the blend mode of the curves layer, or the content of the lower layers, it will have an effect on the appearance of the pixels, even though you haven't actuall applied any curves. Some times is over a layer that has been masked it can soften the mask slightly. Also play with the blend modes. You can easily lighten or darken using this technique, and if you decide that you don't want it, or want to increase the effect it's easy to do.

Thanks both - Chapter 9 Bettedavis.eyes. Nothing underneath it, but change the blend mode to linear dodge, then again later on add another curves layer and change the blend to linear burn.
I guess what your saying is the blend mode sets the curve??
Ali W

I don't have the book, but here is what I understand. If you use a curves adjustment layer without changing curves, you might as well use a levels adjustment layer, or any kind of adjustment layer. What is important is the blending mode: the adjustment layer replaces a duplicate of the underlying layers. The effect is the same, but the file size is not increased as much with the adjustment layer. Please someone correct me if I am wrong...

"I guess what your saying is the blend mode sets the curve??" yes, in a way. The three methods below do exactly the same thing to the underlying layers...

1 Duplicating the underlying pixels and applying Multiply blend. As Michael B says, this creates a larger file.

2 Applying Multiply blend mode to an empty, unaltered Curves adjustment.

3 Applying the Curve I illustrated above in Normal mode. I would attach the ACV file, but can't seem to manage it on this forum.

Another point is if you duplicate your layer, you double the file size, where if you use an adjustment layer you don't. You open the adjustment layer and say ok, then you can set the blending mode. This works the same as duping your layer and then setting the blending mode, however, your file size does not double.
~Nancy~

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As others have pointed out, adding a Curves adj layer without modifying the curve has no effect. If you change the blend mode, then it has the equivalent effect of Duplicating the layer beneath and applying the blend mode at the same time. An adj curve takes up almost no memory whereas duplicating the layer greatly increases the file size (same amount as the layer below occupies). The last effect which no one has mentioned is that when you add an adj layer Photoshop automatically adds a layer mask to it. You can double click the curve to custom tweak it. You can also paint on the layer mask to hide or reveal specific areas. If you had an active selection or loaded a mask prior to adding that adj layer, then that selection will automatically appear on the layer mask. So you get efficiency, flexibility, and virtually no increase in file size with this procedure. Would you use it always? No, sometimes you will need that duplicate layer or a Merged Visible Layer, depending on what else you need to do with the image. However, it is a really useful technique when it fits into your workflow.
Regards, Murray

Hi Hilda,

In the example that you mentioned you are using the layer to add the linear dodge layer. What this will do is greatly brighten the highlights. If you take a look at step 2, she also tells you to invert the mask and then paint on the mask with white. What this does is allow the affect to only be applied to the areas where you are painting on the mask with white. In this case, to brighten the whites of the eyes surrounding the iris.

The blend mode doesn't exactly set the curve, but affects how the layer is applied to the underlying layer. You could, with a little experimenting, do the same thing by setting the curve. You could also make an adjustment to the curve to add, subtract, or otherwise change the affect. You can also reduce the opacity of the layer, to reduce the affect, which is what you are doing when you lower the opacity of the layer to 70%, as listed in Katrin's procedure.

Here is a link to an article from PhotoshopNews.com titled "How to express blend modes as curves" dated September 5, 2007. It talks about using adjustment layers instead of duplicating a layer. Near the end of the article is a link to a zip file that contains the curves for screen, overlay, multiply and soft light.

http://photoshopnews.com/2007/09/05/how-to-express-blend-modes-as-curves/

Thanks to you all, your responses have been really helpful. Now I get it!
Ali W

Just as an aside, this thing about layers increasing file size - is it such an issue?
Wouldn't you flatten the layers at the end of the process anyhow?
OK, so you'd keep a working copy with unflattened layers too but in these days of cheap storage and memory... I have a fairly modest PC in terms of RAM and HD but I rarely, if at all notice any issues with multi-layered files

my files are 800dpi, 8x14" with rougly less than 10 layers of retouching, sometimes less, and a folder full of adjustment layers for color work, any way i can cut file size down, i do!

Most of my files are hi res 16 bit. So the background layer begins its journey at 144MB. When you begin to stack a bunch of these layers there are 2 issues: The file sizes grow and while hard drive space is inexpensive, hundreds of these files will fill the drives quickly. The other issue is that large multilayer files dramatically slow down Photoshop especially if you are one of Photoshop many filters.
Regards, Murray