Sunday, January 31, 2010

Channel mixer to fix a sun flare

I had to fix this photo today: A gorgeous shot, but there's an unfortunate red sun flare very prominent. Luckily, it was a very easy fix, which I thought I'd share here. This is a job for Channel Mixer. I suspect a lot of people have only used Channel Mixer for black-and-white conversions, if they've used it at all. But this kind of problem is just what Channel Mixer was born for. Here's a closer look at the area: First thing I needed to do was examine the individual channels, to see where the damage was. Here's the Red Channel. You can see it's cactus: Here's the Green Channel. It's looking really good: Here's the Blue Channel. It's also looking pretty good, but the poor old Blue Channel is always the grainiest of the three, so it's not ideal: So, what I needed to do was simply replace the Red Channel with the Green Channel in the problem area. To begin, I made a rough selection of the area. I used Quick Mask, but Lasso would have been ok as well: Then I made a Channel Mixer Adjustment Layer. Immediately, of course, my "marching ants" selection was replaced by the layer mask. Channel Mixer opens on Red as the default Output Channel, which was perfect for my needs, because the Red Channel is the one I wanted to fix: To swap a channel is ridiculously simple. I just reduced the Red slider to 0%, and increased the Green slider to 100%. By doing this, I told Photoshop I wanted the red data to be completely replaced by green data on the target output channel. Take a look at the result: Obviously, I could now see that my mask wasn't entirely accurate, because there was a red halo around my adjustment. So I carefully painted my mask to ensure all the redness was gone: Piece of cake! To be honest, sun flares are rarely this easy. Usually it's necessary to adjust two channels, or even all three, and even then there's cloning to be done, or further colour correction. I was lucky that this one was so easy!

Saturday, January 30, 2010

Adjustment layers - strength vs opacity

I got sidetracked from another discussion I was having, and decided to find out if adjustment layers behave differently depending on whether you adjust their opacity or the strength of the adjustment itself. I suspected there would be some difference in results, but I was very surprised at how much difference there is. So, the experiment went like this: I opened an image and duplicated it, so that two copies of the same image were sitting side-by-side on my screen. Then, I'd apply the same adjustment layer to both images ... still looking exactly the same, of course. Then, on the first image I'd reduce the opacity of the adjustment layer to 50%; on the second image I'd go into the adjustment layer and reduce the strength of it by 50% (eg a Contrast adjusment of 40 would be reduced to 20). To read that description, you might expect that both images would still look exactly the same - not so! In some cases, the difference was remarkable. Here's an example, using a Photo Filter adjustment layer. On this one, I used the Warming Filter (85) at 50% density, and left the layer at 100% opacity: Here, I set the density to 100%, but the opacity at 50%: I'm sure you can see the difference, especially in the sky. So, I found that the strength and opacity aren't equivalent for Photo Filter. Nor are they equivalent for Levels, Hue/Saturation or Selective Color. Channel Mixer was very close, but not quite the same. Curves is peculiar. The endpoints don't give the same results when comparing strength vs opacity; but a midtone adjustment is identical! (Well, a modest one, anyway. I didn't test a really strong one that induces clipping). Brightness/Contrast is also interesting. The Contrast slider gives very different results (strength vs opacity), but the Brightness slider gives almost the same. (I didn't dwell on this one too much, though, because B/C is a completely useless tool, and should never be used.) The only adjustment layer that seems to give completely reliable results no matter whether you adjust the strength or the opacity is Color Balance. I haven't figured out why. In all the cases where there was a difference in the effect, I'm not saying that one looks better than the other. They just produce different outcomes, that's all, as the above examples prove. Ok, so what's the point of all this??? Well, for you, dear reader, possibly nothing. For me, not much, because I usually get my adjustments right the first time, and have little need to re-adjust them later, either by strength or opacity. But the differences I saw tonight will make me extra careful about my re-adjustments in the future. The reason I wrote this post is that I know there are some people who habitually make their adjustment layers over-strong, then use opacity to reduce the effect to a satisfactory point. I'll be encouraging those people to re-assess their workflow, to see if they're truly getting the best results.

Monday, January 25, 2010

Straightening horizons

I had to straighten a pic today, and it occurred to me that not everyone knows the trick.

Thanks to my beautiful wife for this one!


Just choose your Measure Tool (probably hidden under the Eye Dropper Tool) and draw a rule along the horizon (or another desired horizontal or vertical line in the photo).

Then go to Image > Rotate Canvas > Arbitrary. Voila! You'll find the angle of the rule is automatically entered there, so all you need to do is hit Ok, and the photo rotates to the perfect angle!

The act of rotation will naturally add some blank triangles into the corners of your image.  So you can go ahead and add a blank layer, choose your Clone Tool, make sure it's set to "Sample: Current & Below" or "Sample: All Layers" in the Options Bar, then clone new detail into those corners if you wish.  (The Content Aware Fill function, if your version has it, can also work sometimes).

Sunday, January 24, 2010

Blend modes ... seriously! WTF?

I just watched ... well, I shan't name names, but it was a brief series of videos on the "important basics" of Photoshop. It started well - Layers. Yes, layers are critically important, no argument there. Opacity. Ok, I guess opacity is important, in a way. Masking. Yes! Masking is damned important, though most people don't use it intuitively, in my opinion. (Article: The right way to use layer masks) Number 4 - Blend Modes. C'mon, give me a break! I see the use of layer blend modes in post-processing very often on the "beginner" forums I frequent. I suspect the author of the aforementioned videos is largely responsible for this. Blend modes are not for enhancing images. Try talking to a pro photographer, or going to the RetouchPro forum (where the real experts hang out) and mentioning blend modes. If you're lucky, you'll be laughed at politely, and gently pointed towards Levels and Curves tutorials. If they're in a mood, you'll be flamed mercilessly. I understand why they're popular among JSOs. They give a quick "wow!" to your photos. Without examining too closely, they appear to improve your photos. They even appear to give you control over your editing. It's an illusion. Blend modes give buggerall control, and can't be relied upon to improve your images under close scrutiny. A Screen layer lightens shadows, but blows out highlights. A Multiply layer darkens light areas, but it clips shadows. An Overlay/Soft Light layer creates midtone contrast, sure, but it brightens highlights and darkens shadows without control; and it does it uniformly, which is rarely desirable. No, ditch them. Take genuine control. Read histograms, use Levels or Curves, master selections. You'll never regret it.

Tuesday, January 19, 2010

Measure the resolution of your screen

Have you ever measured the exact resolution of your screen?

By "resolution" I mean the PPI (pixels per inch) value. Confusingly, there are two definitions of the word "resolution" - one refers to PPI, and the other refers to pixel dimensions, which you probably already know - my screen is 1280x1024.

It's really easy to measure your screen's PPI:

1. Make a new blank document in Photoshop, and set it to 1000 pixels wide. (It doesn't have to be 1000 - if you have a smaller screen, maybe 700 or 800 will do.)

2. When the blank document opens, make sure you view it at 100% (by pressing Ctrl + if necessary). You might need to hit your Tab key to temporarily hide all your palettes.

3. Measure the width of the document by holding a ruler or measuring tape up to your screen. (Be careful not to scratch it!) Jot down the measurement in inches.

4. Then just grab your calculator and divide 1000 (or whatever you used) by the width in inches. The resulting value is your screen's resolution.

I made a 1000px image on my screen, and it measured 11.575 inches wide. 1000/11.575 = 86.4ppi.
I bet you ten bucks that your LCD screen has a higher resolution than 72ppi. 72 is an out-of-date standard, but a lot of people cling to it stubbornly.

Ok, so what's the point?

There's only one purpose for this that I can think of, but it's a handy one. Have you ever gone to View > Print Size and been disappointed that Photoshop didn't actually show you the image at the right size?

If you go to Edit > Preferences > Units and Rulers in Photoshop, you can enter your precise value in the Screen Resolution field.

Then, when you've got an image open and you choose Print Size from the View menu, it will give you an accurate representation of your image size on screen.

Plus, if you're as nerdy as me, it gives a warm glow of satisfaction to be able to say "I know the exact resolution of my screen - do you?"

Thursday, January 14, 2010

What's the purpose of monitor calibration?

This was asked on a forum today, and I thought it was worth elaborating a little ... Why do we calibrate? The common, and obvious, answer is "to make our prints match our screen". Alas, it's not that simple. If we were to assemble a checklist of all the things that have to be perfect for a print to match our screen, it would look like this: [ ] Properly calibrated (and profiled) monitor [ ] Suitable lighting conditions for editing [ ] Correct use of colour spaces and ICC profiles [ ] Soft-proofing [ ] Lab properly profiled [ ] Lab regularly calibrated [ ] Suitable lighting conditions for viewing prints I'm sure I've missed some steps there, but the point is, there's a lot of ingredients in this recipe. Monitor calibration is the first and most important factor. If you're not calibrated, you can forget about reliable print matching, no matter how good the other steps are. But by the same token, a well-calibrated monitor doesn't mean anything if you don't use profiles correctly, or if your lab isn't doing things properly at their end. All the links in the chain have to be sturdy. So the real answer to the question "why do we calibrate" is "because it's an important element in making our prints match our screen".

Wednesday, January 13, 2010

A handy little PC app

Well, I think it's a good time for another post. The kids are asleep for the night, and my wife got an iPod Touch today, so she's buried in that. I don't expect to see her for a few hours! (Although I find it fundamentally abhorrent to have an Apple device in the house, I must admit it looks like a cool gadget!) I was talking to a Forum Friend yesterday, who was having trouble saving a file. She was getting RAM errors when trying to save a jpeg image. Admittedly it was a big image, but her computer has RAM coming out its ears, and plenty was allocated to Photoshop, it seemed. Anyway, I invariably flounder when it comes to system-related issues, and this was no different. I embarrassed myself by making a lot of stupidly obvious suggestions that she had already tried herself, to no avail. I was ready to throw in the towel, but then I suggested this handy little program: CleanUp! by Steven Gould It's a free app that a Tech guy put me onto a few years ago. It does what it suggests - it cleans all the muck out of your Windows system. It worked! My friend was able to save her file. There were happy dances all round. I highly recommend this program. I run it once a month, and it really helps my system speed.

Monday, January 11, 2010

So this is blogging, eh?

Well, here I am. I'm usually hopeless at keeping up with what's modern and trendy (just ask anyone who's seen my dress sense), and it's been no different this time. "Blogs? What are blogs? Oh, they'll never catch on!", I've been saying, as I use my crude stone tools to chip some HTML code into the wall of a cave. In fact, if it weren't for the enthusiasm of my favourite "Moms", and the persuasion and assistance of my beautiful wife (whose nerdiness exceeds even my own) I still wouldn't be here. I'd be ... I dunno, conversing with loved ones, or taking in some fresh air, or something ... but instead, here I am. So this is my blog. I intend to fill it with snippets of my latest work, bits of advice about Photoshop and colour management, and probably the odd rant about Adobe RGB. *shakes fist* And maybe, just maybe, people will read it. For those who don't know me, I'm a Photoshop tragic. I have a part-time home business which I fit around helping with the care of our two beautiful children. I restore old photos, retouch new photos, fix dodgy photos, liquify flabby photos and beautify ugly photos. I spend way too much time on the internet, but hey ... if you're reading this, then you probably do too ;) I'm also a gymnastics tragic. I've been involved in gymnastics for ... heck, most of my life; as a competitor, coach, judge, and advocate. Turns out I'm getting too old for it now - just ask my right knee which is presently recuperating from a ligament reconstruction :( My websites: Belle Photography Brisbane - canvas printing, retouching, restoration and Photoshop training My personal site - My Photoshop portfolio, plus some tutorials, articles and other stuff

Comments or Questions?

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