Photoshop blend modes as curves

[Doug Nelson]

I only understand about half of this, but it is so adorably geeky I had to share:
http://photoshopnews.com/2007/09/05/...des-as-curves/

[cricket1961]

Very cool! Just the stuff I always look for.
Reminds me of the days when you had to make your own gradient maps to load into curves.

Thanks for the link Doug.

Chris

[Ant]

Great article.

[byRo]

A very interesting point in the article, that I had not realized, is that curves are strict 8-bit affairs. If you are using a 16-bit image then the 8-bit curves will not give the exactly correct results that you would get using the blending modes.

So, for me the article goes the other way - "When not to use adjustment layers".

This is not just "geeky" theory stuff. Recently I was using 16-bit images to create 3-D displacement maps. In this case the channel values don't represent colours but physical distances, where every one of those 16-bits counts for something very visible.
The article is a good heads-up to avoid using any adjustment layers on any image where the all of the 16-bits hold useful (though not visible) information.

Rô

[zganie]

Always good to read an interesting article,there is always some tidbit or more
information thanks Doug

zganie

[I. V. Razmanov]

Originally Posted by byRo

A very interesting point in the article, that I had not realized, is that curves are strict 8-bit affairs. If you are using a 16-bit image then the 8-bit curves will not give the exactly correct results that you would get using the blending modes.

It is not so obvious to me. It is clear that author convert "curve" to "map". The latter is, obviously, an array. But it is not so obvious how "curve" work. Does it do any interpolation? How it is constructed? And, BTW, does "map" use any interpolation for 16 bpc?

These are questions I can't answer, mostly because I never worked for Adobe :-)

[Syd]

A really interesting article and I spent my lunch hour playing with it. Not exactly sure what else it can be used for, however. I am not sure if I missed something, though. Was the main point only to show that blend modes can be expressed as curves? Don't get me wrong that in itself was really cool and I was totally engrossed going through the steps. However, it seems to me that if they function identically (with 8-bit files at least anyway) then using blend modes would be much quicker.

Syd

[Stroker]

Curves are like translations.

if input=this then output=that

With regular curves, anchors and what-not, this is done using B-Splines. Second or first derivative or something. And I can't remember which flavor off-hand.

With AMP files, arbitrary maps, the approach is direct like in the if/then statement above. Like an array or a look-up table.

What Martin has done is used RAW to directly edit the AMP, then save it modified. Pretty clever, actually. Folks like me use other languages and fancy-smancy file I/O to do this.

The 8/16 bit thing kind of sucks. A lot of filters out there that boast 16-bit support are actually working in 8-bits. They do 16-bit, but it's faux. Under the hood, things are really done in 8-bits. You will have to test things for yourself to figure out which are faux and which are the real deal.

http://www.thegoldenmean.com/technique/curves1.html

http://tech-slop.serveit.org/amp/index.shtml

http://local.wasp.uwa.edu.au/~pbourk...interpolation/

http://www.doc.ic.ac.uk/~dfg/AndysSp.../BSplines.html

[mistermonday]

Doug, this is really useful, thanks for the link. Using these curves gives you a Curve, a Blend Mode, and a Layer Mask all in the same layer. So after applying it, you can easily mask out areas that you want protected from the blend effect. You can double click on the adjustment layer to fine tune or modify the curve. You can do both of these things without having to add a layer mask or a curve adj layer on top of a normal image layer that had its blend mode changed. And of course the file size is smaller.
There is another positive byproduct. There are many blend modes and it is sometimes difficult to remember what each one does. And sometimes you can't remember the effect of Hard light vs Hard Mix. Adobe describes the general effect of the blend mode but it is difficult to visualize. But now you can take a screenshot of these curves and use them on a reference chart. Looking just at the curve shapes will give you an instant mental image of what the effect of that blend mode will be on your image without actually having to apply it or cycle through all of the various blend modes to find the one that looks right. Like spome many other things in PS, this is just another option available to assist your workflow if you are it works and you are comfortable with it.
Regards,
Murray

[Markzebra]

Yes its great to have this pointed out finally ..that duplicating image data and appling blend modes to them is not less destructive than using Curves because I've worked with people who are happy to needlessly generate 2G files with multiple copied sections each with Multiply and Screen applied.

I remember very early on seeing these blend modes curve equivalents posted somewhere else, and had never been able to find it since.

A great link