Color Transparency

[MikeFromMesa]

I have been playing around with the new version of PhotoLine (version 19) and especially the Color To Transparency (CTT) functionality. That functionality is new from the last release but, I guess, was in the betas before the release of version 19.

I loaded an image that had a particularly uniform gray background and removed the background with only 2 color selections. I was so impressed that I loaded up a more difficult image to try to see who the CTT functionality worked with it. However it seems that the CTT dialog box remembers the last color selected, even from a previous image, and it immediately removed the same colors it had before. I tried to reset the dialog box, but that only removed even more of the image. Is there some way to reset the CTT functionality so that it does not remove any of the image?

A second question. I noticed that when I select the blue in a sky to remove it, it does a wonderful job of turning that to transparency. But when I then select one of the white clouds PL replaces the blue in the sky as though it can only remove one color. There is, of course, a tolerance setting, but are the colors selected meant to be additive or not? And does selecting white replace the other colors because the dialog box only accepts a single color? Or because white is meant as some reset value? I am so new to this dialog box that none of it is clear to me.

[photoken]

I tried to reset the dialog box, but that only removed even more of the image. Is there some way to reset the CTT functionality so that it does not remove any of the image?

No, the dialog uses the last colour specified in the dropdown colour selector as the "reset" colour. Either select a new colour in the dropdown box at the top, or use the eyedropper to select a colour in the image.

A second question. I noticed that when I select the blue in a sky to remove it, it does a wonderful job of turning that to transparency. But when I then select one of the white clouds PL replaces the blue in the sky as though it can only remove one color. There is, of course, a tolerance setting, but are the colors selected meant to be additive or not? And does selecting white replace the other colors because the dialog box only accepts a single color? Or because white is meant as some reset value? I am so new to this dialog box that none of it is clear to me.

Yes, it can only remove one colour -- it's not an additive colour specifier. To remove multiple colours, use the CTT as an adjustment layer and create one for each colour.

Some additional examples of the power of CTT --
Removing colours from transparent objects:
http://www.pl32.com/forum3/viewtopic.ph ... ncy#p28490
Converting a ChromaKey background to transparency:
http://www.pl32.com/forum3/viewtopic.ph ... ncy#p28491

[Alan9940]

Like Mike, I've been playing around with PL v19 and am baffled by the new Color To Transparency adjustment layer. Based on what I've read here on this board and in the Help file, I assumed that I could drop out a single color such as clear blue sky. This would prove extremely useful for replacing dull, cloudless skies in landscape images. However, I have an image where blue sky is literally the only blue in the image, but when I duplicate my background layer, create the CTT adjustment layer, use the eyedropper to select the blue (adjusting the Hue slider up slightly to ensure grabbing all the blue variations), and click OK, I have semi-transparency showing through in image areas that aren't blue!

OK, I realize that other colors also contain some blue component, otherwise we wouldn't have images based on R-G-B. Is that why image areas that are, for example, yellow revealing some transparency? Is there a way to restrict this tool to the selected color in specific image areas? Or, am I trying to use the CTT for something it was never designed to do?

Thank you for any help provided.

Best regards,
Alan

P.S. As I was re-reading what I wrote above I had the thought that maybe I could use a loose selection of the sky to restrict the CTT layer? Hmm....gonna try that!

[photoken]

Hi Alan,
If you wouldn't mind posting a sample of the problematic image, we could take a look at it.

In general, if you're using the "Similar Colors" option at the bottom of the dialog, the three sliders and the adjustable Histogram become very important for targeting the colour. Experiment with them to get the result you're looking for.

An important point is that the CTT respects masks, so you can protect areas from being affected. For example, if you have a pale gray, washed-out sky you want to make transparent but also have aspen trees in the foreground, you can first paint a mask over the tree trunks to protect them.

Added:
I re-read your message and I think that you're moving the Hue slider the wrong way -- reduce the tolerance to target only the blue colour of the sky you selected.

[photoken]

am I trying to use the CTT for something it was never designed to do?

Essentially, the CTT was added to eliminate the need for additional plugins such as KillWhite (which does not work in PL). As CTT was refined and enhanced, its power and versatility increased significantly beyond that original intent.

[Alan9940]

Hi Ken,

Thanks for the input!

After reading your post, I played around with CTT some more and what I discovered is that the histogram looking box enabled me to, basically, unselect transparency in foreground areas that weren't any shade of blue. I had to slide the right-side bar about halfway to the left, and I have no clue what it's doing, but it did do what I wanted. No idea what the Brightness or Saturation sliders are supposed to do. I moved both these sliders full right and full left, and the semi-transparent areas really didn't change much though the foreground image areas sure seemed to be affected. So, to completely eliminate the blue sky I used two CTT's and moved the Hue slider left, as you suggested, creating the first CTT for mid-blue values and the second for light blue values. It all worked pretty well, except that I could clearly see "blue fringing" around the distant and somewhat soft (due to atmospheric haze) tree line. Moving the right bar of the histogram to the right for the light blue CTT layer enabled me to pretty much eliminate that "blue fringing", but then too much of the blue returned. Perhaps a third or forth CTT would fix that? Dunno, but I'll play some more!

If you have any idea what the Brightness and Saturation sliders bring to the table, I'd love to know what I should be expecting to see. Basically, what I was hoping the CTT would do is give me a more accurate Automask!! It still might, but I'll have to experiment more...

Best regards,
Alan

[photoken]

If you have any idea what the Brightness and Saturation sliders bring to the table, I'd love to know what I should be expecting to see. Basically, what I was hoping the CTT would do is give me a more accurate Automask!! It still might, but I'll have to experiment more...

The Histogram at the bottom is kind of the key as to what's going on. As an example, move both the left and right adjustment triangles somewhat towards the center. Then move the Saturation and Brightness sliders and you'll see the peaks and valleys of the image values shift into and out of the affected range.

Other than that, I don't have an "official" description of the controls -- what I've learned is just by trial-and-error for each image. But, invariably, when I use the controls to do the first adjustment on an image I get all f*ed up, and have to reset and start from scratch....

The thing about a blue sky is that, depending on the angle of the photo in relation to the sun, although it might seem to be a uniform blue, it really isn't -- it can take up to three CTT adjustments to get rid of it: one for the blue at the horizon, another for the blue at the top of the image, and maybe another for the blue halfway between those two.

As with any tool, though, there are bound to be some images where it just doesn't do everything desired all on its own -- first painting a mask to protect the foreground areas is sometimes a very good technique.

[MikeFromMesa]

Yes, it can only remove one colour -- it's not an additive colour specifier. To remove multiple colours, use the CTT as an adjustment layer and create one for each colour.

Some additional examples of the power of CTT --
Removing colours from transparent objects:
http://www.pl32.com/forum3/viewtopic.ph ... ncy#p28490
Converting a ChromaKey background to transparency:
http://www.pl32.com/forum3/viewtopic.ph ... ncy#p28491

Thank you for the response and the information. I was unable to respond properly yesterday due to other obligations, but I did appreciate your speedy posting and the information.

[MikeFromMesa]

Hi Alan,
An important point is that the CTT respects masks, so you can protect areas from being affected. For example, if you have a pale gray, washed-out sky you want to make transparent but also have aspen trees in the foreground, you can first paint a mask over the tree trunks to protect them.

I was having the same issue as Alan with the CTT Tool affecting much of the rest of the image. I had thought that I could select only the sky portion of the image and then apply the CTT Tool to that selected area to restrict it, but that did not work. I will next try to use several layers to try to restrict the area where the CTT Tool actually has an affect.

It would be nice to be able to get this to work because selection/masks are the one thing I continue to have troubles using in PL.

[bkh]

If you have any idea what the Brightness and Saturation sliders bring to the table, I'd love to know what I should be expecting to see. Basically, what I was hoping the CTT would do is give me a more accurate Automask!! It still might, but I'll have to experiment more...

As far as I can see, the "Saturation" and "Brightness" sliders control how much these values affect transparency. If you set "Saturation" to 0, then even colours with little saturation but the same hue as the colour swatch will become transparent, if you set it to 200, then only colours with almost the same saturation will become transparent. "Brightness" is similar.

According to the manual, the histogram is the historgram of the alpha channel. Normally, you should make sure that some parts of the image become fully transparent (the histogram has value near the left edge) and some will remain fully opaque (values on the right edge).

Cheers

Burkhard.

[Hoogo]

I see CTT not that much as another tool to select and remove a color range. I see it more as a tool to remove color casts from semi-transparent areas.

Imagine some semi-transparent white in front of a blue background, for example clouds.
You want to have a picture with clouds only, so you somehow want to turn the blue smoothly into transparency.
In the picture there's a gradient between the blue background (0% cloud) over a light blue (50% background + 50 % white cloud) and white (100% cloud).

Other tools like select colors can also turn that gradient of colors into a gradient of transparency.
But other tools will not affect the color within that gradient. 50% transparency and light blue will go together, so there's still some color of the old background in the result.
CTT will change the color and turn the light blue into white. And that's most useful if you want to exchange the background.

[photoken]

I had thought that I could select only the sky portion of the image and then apply the CTT Tool to that selected area to restrict it, but that did not work.

That should work. Here's a screenshot of CTT where you can see that it's only affecting the selection area (at the top):

CTT selection.jpg

[Alan9940]

@Mike - The more I play with CTT I'm starting to understand that it's not really meant as an "Automask replacement" (though I was trying to use it in that manner), but more for removing color from transparent areas of an image; such as a bridal veil against sky, for example. I haven't tried using CTT in this manner, yet, but I plan to find such an example image and continue experimenting. I really think it's all going to boil down to that CTT is simply another tool that when combined with other tools will allow you to perform magic!

@bkh - Your definition of the "Saturation" and "Brightness" sliders certainly seems logical, but so far my experience hasn't proven this to be the case. I was playing with a test image, yesterday, that had mostly even blue sky with yellow-to-cream colored homes in the foreground, and light gray to "whitish" sidewalks in the mid- and foreground areas. Also, quite a bit of green vegetation everywhere. When using the eyedropper to select the blue color in the sky, the sky pretty much goes fully to transparency (adjusting the Hue slider a bit); but the color values in the homes and driveway areas reveal some transparency, too. As I move the "Saturation" and/or "Brightness" sliders from full left to full right (0% - 200%?) the semi-transparency areas in the homes and driveway go from slightly less semi-transparent to slightly more semi-transparent. These areas never return to fully opaque moving only these two sliders. What's additionally strange, is that the saturation slider seems to affect the actual saturation of these semi-transparent areas. Seems pretty weird to me! However, if I leave both sliders at 100% and move only the left bar of the histogram inward to the left at about the midpoint of the histogram the semi-transparent areas return to fully opaque! I guess what I'm finding more than a little confusing is why any of these controls affect anything other than the blue color originally selected?

@Hoogo - The more I play with CTT the more I'm beginning to agree with your idea of what CTT is for; my bridal veil against blue sky idea?

Best regards,
Alan

[Alan9940]

Hi Mike,

But the mountain area has also gone somewhat transparent which is to be expected since there is so much blue color in that area. However, see the attached...using the eyedropper I selected the clear blue color of the sky and adjusted "Hue Tolerance" to 20% which gave me full transparency in the sky. But, look at the front of the garage and top of the garage door both of which reveal some transparency. Why? This image area is a light chocolate truffle coloration. Additionally, you can clearly see that the hue of the originally color has changed, too. My guess is that the blue component of the R-G-B value in this area is gone; hence the hue shift? If you look closely, you'll also see that the green/yellow of the ococillo has also been affected.

All that said, I'm beginning to believe that CTT is not really meant to be used this way; not that we all haven't forced other PL tools into submission to do things they maybe weren't originally intended for!

Best regards,
Alan

[MikeFromMesa]

@Mike - The more I play with CTT I'm starting to understand that it's not really meant as an "Automask replacement" (though I was trying to use it in that manner), but more for removing color from transparent areas of an image; such as a bridal veil against sky, for example. I haven't tried using CTT in this manner, yet, but I plan to find such an example image and continue experimenting. I really think it's all going to boil down to that CTT is simply another tool that when combined with other tools will allow you to perform magic!
Alan

Alan,

I had the misfortune (if that is the correct word) to first use CTT on the following image:

https://www.dropbox.com/s/bq8je9qofmea9 ... 2.jpg?dl=0

The background was so uniformly gray that it took only one try to get it completely removed more cleanly than I would have thought possible. It gave me the idea that CTT was perfect for removing backgrounds for layers work, but when I got involved with more complex images I found out that my initial thoughts about using the tool were overly optimistic, at least as far as easily removing backgrounds.

I am now investigating the Dehazing Tool.