Channels & Masks Video Lesson 6: "The 25 Standard Blend Modes"

I personally find Photoshop blend modes to represent one of the secret handshakes of the Obscure Brotherhood of Photoshop. There's no reason based on name or description that you would be able to intuitively know what these mathematical mixings of pixels will do to your image layers. But in this latest video from Deke's new book Photoshop CS4 Channels & Masks One-on-One, Deke gives you a darn good run down on what the 25 standard blend modes actually do and how to think of them in groups for better predictive behavior. If you've always wanted to know what to expect from blend modes (you know, something more sophisticated than randomly clicking through them), this will help get you started.

If this whets your appetite for more, as it darn well should, the book is available now, and it contains exercises that allow you to put this revealed knowledge to use in real-world projects. Ah, Enlightenment.

 

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Comments

Divide (unmult) Blend Mode?

I actually need a 'divide' blend mode for something I'm working on. At least I think I do. And, no, it's not because I'm having some sort of premultiplied alpha compositing problem... Is there such a capability in Photoshop? ... I need to divide a textured and lit plane in a CG program by the same plane lit lambert white so that the texture map becomes extra bright and 'inversely shaded and lit.' Then when I reproject the bright image onto the plane and light it, the lighting will reduce it to its original colors and values. If this package had what Maya calls a 'surface shader' that accepts a map without regard to lighting, I could avoid this runaround, but I think I may need to do it. The purpose of this is to have a photo into which I can accurately refract, etc, without letting the scene's lighting change the already correct photo. I'm considering rendering single frames in Adobe AE using the 'unmult' plugin. I'm also considering (gasp!) the Gimp.

Histogram details

Dear Deke In the sidebar "Unearthing JPEG Artifacts with Difference" in the book, you mention at the end that the Histogram palette shows that more than 84% of the pixels have changed. With my (too) limited knowledge of the Histogram panel(!) I would like to know how you find that information. Maybe you mention this in another one of your books or videos?

Would like to know too

That's a neat little trick in this sidebar. It gives a clear idea of how much is different. The histogram I get is a series of thin lines whereas the furthest left line has a statistical value of 89%. The value of 84% is between the lines. I am guessing that the far left line's value would represent the percentage of pixels changed. The actual number is not of much value really, but understanding how the graph relates to the values helps to understand the math behind the Photoshop functions.

I may be able to help

Not sure if this is the method Deke uses (I don’t have his CS4 book), but this is how I would do it: -Open a non-jpg image* -Choose Image/Duplicate -Save the copy as jpg @ setting 12 and close it -Open the image you just saved; now it will have the jpg artifacts regardless of how invisible -Drag and Shift+drop it onto the original image to create a jpged layer -Change its blend mode to Difference. Any pixels that are identical to the layer below will stay absolute black; others will vary ever so slightly -Create a threshold adjustment layer and set it to minimum value (1). Any pixels that are more than 1 brightness levels apart will turn white -Now let’s get those pixels that are just 1 brightness level apart and make them white as well: Create a levels layer and drag it just below the threshold one -Move the white slider all the way to the left. That will draw out the pixels that are only 1 brightness level brighter than black -In your Channels palette Ctrl+click on the RGB (composite) channel. Mac users, use the command key instead of Ctrl -Go to histogram palette and look at the number at the bottom left corner (“Pixels” value). That is the number of pixels selected, ergo the number of pixels that are different in the jpged layer. -Divide that number by the number of pixels in the image (Ctrl+D t deselect and the number changes to the total number of pixels) and multiply by 100. That’s your percentage and it should be above 60 in best case scenario. And to boot, that’s with the best quality jpg, too! If you try experimenting, you may be surprised to find out that with a certain number of images, the percentage of pixels that changed doesn’t vary too greatly with the more fecal compression. What varies is how far pixels have drifted away from their original state. To find that out, try using a threshold of 128 instead (without the levels layer) and see the difference then. _________________ *If jpg is all you have, open it and reduce its size to recalculate pixes and start anew. You don’t want to be piling up the jpg compression atop of jpg compression

Overlay and Soft Light

From what I've noticed, putting white over a layer using 'soft light' returns the square root of the layer below. It looks a lot like the layer screened on itself. Putting black over a layer using 'soft light' returns the square of the layer below. It looks the same as the layer multiplied by itself. Putting white over a layer using 'overlay' returns the cube root of the layer below. It looks a lot like the layer screened on itself once, and then once again. Putting black over a layer using 'overlay' returns the cube of the layer below. It looks the same as the layer multiplied by itself once, and then once again.

I've seen suggestions

Of squares and square roots used in Soft Light. (There seems to be a fair amount of conjecture on that mode, and Adobe doesn't share its equations.) However, Overlay and Hard Light are well documented. Where A is the active layer and B is the composite background, 0 = black, 1 = white, and 0.5 is gray: Overlay is If B > 0.5, 1–2(1–A)(1–B) If B < 0.5, 2AB Hard Light changes only the conditions If A > 0.5, 1–2(1–A)(1–B) If A < 0.5, 2AB I've considered posting a blend mode equation round-up. Not sure how many folks would be interested.

Overlay and the A Layer

It's very strange, since retouchers seem to use 'overlay' as a form of 'dodge and burn.' - and their technique is driven by the A layer. If I'm not mistaken, a retoucher will often fill an A layer above the composite background with 50% gray. That has no effect on B. Then they go in and paint whites and blacks (lighter and darker grays) into the 50% gray layer to 'dodge and burn' B. Is it possible that they think about it backwards, and that the math happens to work out in such a way as to give them a wrong idea about which layer is in the conditional statement? I'd have to look closer.

Yes to Blend Mode Equations!

I'd certainly be interested in seeing a round up of blend modes and their respective math! Am I sad for thinking that would be interesting?

me! me!

Wow! I would be GREATLY interesting in seeing blend mode equations! You know, a picture is worth a thousand words - and, likewise, an equation is worth a thousand colorful descriptions of how blend modes work. That doesn't include YOUR descriptions - yours are better than equations, better even than a cheese sandwich. :))

I'd also be seriously

I'd also be seriously interested in an opportunity to see the blend mode equations. My brain likes such things to grab onto. The equations of course would be meaningless without your illustrations. You might get the impression here that some people are trying to encourage to post the math by being honest. Definitely guilty as charged. Anyway, it would be really cool to see the underlying math if you have time to post it.

or maybe

Or maybe you could include a PDF file with formulas among the exercise files for your forthcoming Blend Modes course. :)

Well that will definitely happen

In the meantime, let me research my facts. This may be one of those group efforts where we as an enlightened quorum take equations and run tests to gauge their veracity. Blend mode math in progress, as it were. B/c I'm pretty sure the jury's still out on a few of them. btw, I've published the math for Screen, Multiply, Difference, Exclusion, and a few others in my Channels & Masks book. But exploring them all is, if nothing else, and interesting exercise.

Channels & Masks Arrives in the UK!!!!

Wow, just got my copy of Photoshop CS4 Channels & Masks via Amazon (had ordered it before Christmas) and having just flicked through it I can definitely say that is has been worth the wait! Great job on the book Deke (and the rest of your team), I can't wait to start reading it! See Yaaaa!

CS4 Channels & Masks in UK

I just got mine today from Amazon. Looks like a great book ... only one question so far: I've just loaded Deke's "Best Workflow CS4" into PS and I notice that the CMYK setting is for US Web Coated (SWOP) v2. This is not appropriate for this side of the pond. Can anyone tell me whether my files will be affected by this? I don't particularly want to syncronise my CS4 Suite settings to US process settings. Thanks Steve

Change CMYK to whatever you want

It will not affect your enjoyment or understanding of the Channels and Masks book or any of my other products. The Color Settings are really all about getting RGB set to Adobe RGB and Intent set to Perceptual. It is a given that you will change the CYM settings to your commercial printer-specific space. Let me know how you like the book as you make your way through it!

A Place to Blog...

OK Deke...So I am pretty new to the online training...but found lynda.com's site to be very helpful, the CS4 One on One Training with you to be great, even though I thought I already knew everything...then found your website. I have however ran into an issue. In CS4 when I transfer a layer into another document, it will not transfer by dragging it up to the other layers tab as you did in your video. And there does not seem to be a special button I need to have on or off for this. It would be great if lynda.com's website could have a blogging section for it's users where they could have additional questions they're having answered, beyond the scope of what is being taught. Even if there is a fee involved. That would be great....seeing as I am hooked now!

Is there a way to save this

Is there a way to save this video to my hard drive? I don't see a "download" link...

Not yet, but there will be

I plan to make the first six videos available to members for download sometime this weekend. They'll only be up for a limited time so be ready!

great!

Thanks, Deke! PS You rock! :))

Rock on

The first batch of savable videos are up here.

CS4 Channels & Masks Video Series?

Deke, I'm sure your new C&M book is fantastic. But for those of us hooked on your videos, will you be recording a full CS4 C&M series on LDC like you did for CS3? That is still some of the best stuff I've seen. Thanks. DP

Possibly....

I notice that in the Channels and Masks book Deke comments that their could possibly be a CS4 Channels and Masks video series, so who knows! I guess the problem Deke faces is that there's been no radical changes from CS3, so would it really be worth recording 32 hours of training for a few small (reletively) changes? Mind you, I wonder if Deke has ever thought about recording, say a couple of hours of video, called something like 'Channels and Masks in CS4 - New Features', so new users could watch that and then view the 32 hours recorded using CS3 (or vice-versa)? Sure would save him a couple of weeks! Matt

Possible video titles

Just so's everyone knows, here's the plan: Finish Photoshop CS4 One-on-One. Just 18 more chapters, maybe 300 movies, so no pressure there. Finish Illustrator CS4 One-on-One. Same number of chaps and movies. I'm too late for InDesign, so once again, I leave it to David and Anne-Marie. Check into rehab. Make a few dekePods. Return to civilization. And then record a few Photoshop "vertical market" videos on the following: Smart Objects Blend Modes Color Adjustments Channels & Masks (CS4) Which would you prefer first? Anything I'm missing?

I Vote For.......?

Hmmm yes that is an difficult choice. I loved Channels and Masks, without a doubt the best video series I've ever watched.....ever! But seeings as there's so little change I guess I'd love to see one of the other subjects tackled. Blend modes was covered in C+M, and when you say color adjustments do you mean something along the lines of the Lab series you did at Lynda.com? Smart Objects would be great too! I think, after much debating, I'd go with color adjustments! Do it Deke, you know you want to!

a difficult choice :)

Well, that's sure a difficult choice. But you've already covered Channels and Masks so-o-o comprehensively - it would be great to see an equally detailed video course on some other topic. I am sure color adjustments, blend modes, and filters would be all excellent topics.

Rough

Wow, your going to tackle CM again? That series was huge! You could do a series on just the filters alone. What color adjustments examples were you thinking about? Mmm Cookies!

What does "vertical market" mean?

And I'm outta rehab now. As splendid as it was, it didn't really work - I'm still addicted. ;-p

It means deep down dive

And I'm sure you, Petra, of all people have something to say about that. ;-) (Vertical market = the folks who are no longer interested in the horizontal skim across the many seas of products and are now interested in taking the plunge into the one lake of choice: e.g., the many details of Photoshop.) Enjoy your vacation!

LOL

Oh, dear. I appear to have developed a reputation. Go me!!! :-D And I did enjoy my vacation! It was fabulololous. Never been happier. :) Thanks for the definition - I'd not heard it before. I guess it's like the difference between snorkeling and free diving; and perhaps that is where the term originates? I might start a new meme for girl fans of dekePod. We can be the freestylin' breast strokes. Don't suppose you could lend a hand? :-p

Nah

He pretty well covered it in the CS3. I would love to see something new, like Smart Objects, Crazy Fun, Text graphics. There is no limit to what Deke can teach. Plus, that book cook his goose for a little while. But of course Deke could do it, WITHOUT A DOUBT! Mmm Cookies!