Problem with "blend if..."

Jack'll do

Took the following image on a grey overcast day and wanted a blue sky background. I placed a sky image behind it and used "blend if" to accomplish a better background. All around the image there are very light pixels from the earlier gray sky (this can be seen better in the second image which is a screen capture of the first at 300%). I fiddled with the sliders a lot in the blend if dialog but could do no better than this. What am I doing wrong or is there no alternative but to go in and clone them out pixel by pixel?

jfriend

Jack'll do wrote:

Took the following image on a grey overcast day and wanted a blue sky background. I placed a sky image behind it and used "blend if" to accomplish a better background. All around the image there are very light pixels from the earlier gray sky (this can be seen better in the second image which is a screen capture of the first at 300%). I fiddled with the sliders a lot in the blend if dialog but could do no better than this. What am I doing wrong or is there no alternative but to go in and clone them out pixel by pixel?

We would need to see what the original image looked like (in a fairly large size) to offer you suggestions for how to better accomplish this. Techniques and settings for sky replacement are very dependent upon the particular image and what colors and tones it has at the sky boundary.

Jack'll do

John
Here is the original RAW image converted to jpg and 72ppi with no PP. Does this help?

Nikolai

I apologize if I'm asking a trivial thing, but you *did* try split sliders, didn't you?

Jack'll do

Nikolai wrote:

I apologize if I'm asking a trivial thing, but you *did* try split sliders, didn't you?

Not trivial at all Nik. I should have mentioned that I did use split sliders.

Nikolai

John,
I've tried it at home. I believe the problem lies with the combination of the aliasing and CA, especially noticeable at lower res. The halos you're getting have the same nature as the ones you get from a heavy hand sharpening.

My suggestion:
1) start from RAW, go 16 bit (or even 32 bit)
2) in RAW (or in PS) perform a major defringing and anti-aliasing action
3) do the blendif again
4) You may need to perform some borderline painting/cloning with non-trivial (lighter or darker) blending mode to fine tune the edge.

HTH

Jack'll do

Hi Nik
I did the defringing in ACR. Then opened the 16 bit image in CS3 but cannot find any antialiasing action. My actions panel only contains the default folder and I don't see any mention of antialiasing. Am I missing something?

P.S. I did a google search and from what I can see, I must select the part of the image I want to apply antialiasing to. Is that what you mean?

Nikolai

Jack'll do wrote:

Hi Nik
I did the defringing in ACR. Then opened the 16 bit image in CS3 but cannot find any antialiasing action. My actions panel only contains the default folder and I don't see any mention of antialiasing. Am I missing something?

No you're not, I simply meant it in a generic way, my apologies.
OK, did you do all these things (16-bit, defringing) before, too? If not - what you you try just that and see how it goes?

Jack'll do

Nikolai wrote:

No you're not, I simply meant it in a generic way, my apologies.
OK, did you do all these things (16-bit, defringing) before, too? If not - what you you try just that and see how it goes?

Yes I always shoot in RAW and make initial adjustments in ACR then open the 16 bit file in CS3. I did not defringe the first time. I will try the blend on the defringed image tomorrow (getting late and we're expecting a big snow in the morning. gotta get some sleep). I'll post the result when done.

P.S. check my P.S. in my previous post.

Nikolai

Antialiasing can be tricky. You may simply need to make some bright pixels darker, something like have find edges, or whatever, and doing some rough darkening.

jjbong

Jack'll do wrote:

What am I doing wrong or is there no alternative but to go in and clone them out pixel by pixel?

I can't explain why Blend-If isn't doing the trick.

I tried a different approach and got better results:



I used a mask to blend in the (here completely blue) sky.

Since the sky in the original shot is blown-out, the Lightness channel in LAB is a good start. I applied a couple of extreme curves to drive everything to black and white, and then used to dodge and burn tools to refine it. I did some crude painting of black into the interior of the building in the Lightness channel).

The hardest part was the yellow spire on the right side, which got washed out in the above. Since this is yellow, the B channel in LAB helped out. I filled it with 50% grey, lighten mode, and then did an auto-levels on it, then blended it into the Lightness channel in darken mode.

The resulting Lightness channel is a reasonable mask, with a little problem on the edges. I turned it into a selection expanded it by 1 px, and then turned it back into a mask.

This mask on a layer of blue (or a sky) is what you see here.

The whole thing took less time than to describe it, with no really detailed moves. All of this in 8-bit, by the way.

If this is unclear, I can expand.

jjbong

By the way, I use Blend-If all the time. I find it works really well for adjustments that involve pretty gross differences in some attribute that you have a handle on (a channel). But it doesn't seem to work so well for finer work, like your shot.

The nice thing about masks is that you can modify them in a lot of ways. You can fine tune parts of them, you can do subtle global adjustments (like expanding or contracting them by a small amount, blurring them, etc.). Blend-If is quite crude in comparison. Sometimes that's OK, and sometimes it's not.

Jack'll do

Thanks John
I too have always used masks in the past. But if "blend if" works it simply is much faster for me. I had not considered working in different channels tho so I will keep your post in mind for the future. (I'll be probably be contacting you for help tho )

I'd really like to see your final image using your method.

Jack'll do

Nikolai wrote:

Antialiasing can be tricky. You may simply need to make some bright pixels darker, something like have find edges, or whatever, and doing some rough darkening.

Hi Nik Happy New Year to you and yours.

First thanks for pointing me in the right direction here. The defringing helped reduce the jaggies but when "blend if" applied was still not acceptable. There was now a darker blue area around the interface of the two layers plus a narrower whitish edge. I ended up having to clone that out by tracing the entire edge of the interface. Here's what I finally ended up with. (I started with the original RAW file but did not do any perspective correction as I had with the one I first posted... you may notice that difference. In the original attempt, any sharpening with smart sharpen or even hpf made the problem worse. In the final image I was able to sharpen a bit and use a light hpf without that problem. I have spent way too many hours on this. I'll think twice before doing it again.

Nikolai

Jack'll do wrote:

Hi Nik Happy New Year to you and yours.

First thanks for pointing me in the right direction here. The defringing helped reduce the jaggies but when "blend if" applied was still not acceptable. There was now a darker blue area around the interface of the two layers plus a narrower whitish edge. I ended up having to clone that out by tracing the entire edge of the interface. Here's what I finally ended up with. (I started with the original RAW file but did not do any perspective correction as I had with the one I first posted... you may notice that difference. In the original attempt, any sharpening with smart sharpen or even hpf made the problem worse. In the final image I was able to sharpen a bit and use a light hpf without that problem. I have spent way too many hours on this. I'll think twice before doing it again.

Gald you managed to conquer this issue to your liking. It was a nasty edge problem, there is no silver bullet for those. It's always "availalbale time vs final quality" battle.

Happy New Year to you, too!

jjbong

Jack'll do wrote:

I'd really like to see your final image using your method.

Here it is, with a layer with uniform blue for the "sky".

Jack'll do

jjbong wrote:

Here it is, with a layer with uniform blue for the "sky".

Thanks John
That worked out very nice.

jjbong

Jack'll do wrote:

Thanks John
That worked out very nice.

I did this in PS CS3. I've seen posts from pathfinder and probably others about the smart selection tool in PS CS4. I'm curious whether this would have worked here.

pathfinder

I have been meaning to add to the discussion in this thread - I started with a sky replacement via the Blend if commands, with this result which I didn't like that well - but I just used the smaller file here in this thread

My real answer is here

jjbong

pathfinder wrote:

I have been meaning to add to the discussion in this thread - I started with a sky replacement via the Blend if commands, with this result which I didn't like that well - but I just used the smaller file here in this thread

Thanks. I didn't realize Quick Select was in PS3 - thought it was new with PS4.

pathfinder

Quick Select and Refine Edges did not get a lot of discussion with the introduction of CS3, (and I did not like it until I got a newer, faster Mac - I had a G5 previously ) but once I got a dual processor Intel Mac I rarely use any tool for selection other than Color Select and Quick Select, or Quick Mask.

By painting inside and outside the box I can isolate my selection pretty quickly. Refine the edge, and I am done.