How can you convert to black and white and retain one colour?

I am not sure, what you want to achieve; but if you want one colored object to stand out in a black & white image, use a "Black&White" quick-fix and then "Brush Black&White Away" from the options behind the cogwheel in the "Black&White" brick.

You can also use the Color brick to remove specific colors from an image. Add Color and click the eyedropper. Then click a color on the image and drag the saturation slider to the left. Add more Color bricks (using the gear menu) to remove additional colors.

I suppose that's the opposite of what you wanted. But it's kinda fun.

But it's kinda fun.

😀 😎

Thomas Emmerich wrote:

Add more Color bricks (using the gear menu) to remove additional colors.

The Color Brick, like a few other Bricks, is, in effect, "tabbed", with all the tabs active, even though it hides this by default. There is no need to add additional Color Bricks -- you can use all six of the hue tiles shown, at the same time. Additionally, there is nothing preventing you from assigning _any_ hue to _any_ tile. The ones which show by default are there by convention.

The Color Brick, in fact, makes a terrific tool for experimenting with, and learning about, hue and saturation. Rather than ruin the fun, I will simply pose this as a question: what settings will turn any image into a grayscale?

To select a "tab", click the hue tile. To see all the "tabs" of the Color Brick at once, click the "Switch to expanded view" icon -- it's the left-most of the three icons at the top right of the Brick.

(Added Bonus:)

Once you have an answer to the question above, create a new Version from the Original ("⌥g") and apply the Black & White adjustment. They are different. Why?

Message was edited by: Kirby Krieger -- former teacher of color.

Kirby,

I thought the answer to your question was obvious until I tried it. I lowered the saturation for red, green and blue to the minimum (-100) and increased the range to max (20.00). But in my test image I still had color where there used to be red and yellow. Nothing I did in the Color brick got rid of it. Eventually I figured that the image highlights were overblown. When I reigned them in, the color was gone. The image was from a p&s camera taken in bad lighting at a skating rink. So although I would have thought the adjustments I did in the color brick would make any image B&W, it doesn't work on an overexposed image. Does that make sense to you?

Thomas -- not what I intended 😊 -- you seem to have found the exception that probes the rule.

First, I'm not sure how broad the full expanse of the range parameter is (the User Manual refers to this as the "chromatic spread"). (And, of course, the distribution of the effect within the range is very not linear.) Did you change range and saturation for just R, G, & B, or for all six default hues (RYGCBM)? (This last better recognized as RGB with CMY interleaved by hue.) Afaict from the User Manual, "10" = 120°. "20" may be equal to 240°. What I'm trying to make sure of here is that the hues left with some saturation were in fact covered by the range settings in aggregate.

Second, a guess: the saturation adjustment is normalized to the current gamut. Pixels outside that gamut are either not effected, or are adjusted absolutely rather than proportionately. (In effect, colors outside the gamut have their saturation expressed numerically as greater than 1, and are being reduced by 1 rather than by 100%.) As you cleverly figured out, bringing all pixels inside the perimeter of the colors possible gives the result you (and I) expected. (I would think the saturation adjustment should be always calculated as a percentage of the starting value ... but I don't know how Aperture works at this level. Léonie, iirc, has done work with "machine color" -- perhaps she'll take note and throw us something reliably bouyant.)

Did you happen to check for the RGB parameters for pixels that still showed color after minimizing saturation and maximizing range for the default hues in the Color Brick??

Léonie, iirc, has done work with "machine color" -- perhaps she'll take note and throw us something reliably bouyant.)

😁 Sorry to disappoint you, Kirby. I've done some research on color processing, that's right, but I don't know for sure what Aperture's color brick is really doing. I am frequently surprised by the results.

Your guesswork sounds rather convincing.

Glug ...

😝

Thanks for jumping in. It certainly would be helpful if Apple, Adobe, NIK, etc. published information indicated what the controls and filters do to the hue, saturation, and luminance values that define each pixel.

With RGB saturation set to -100 and range to 20, the other 3 default color saturation adjustments in the Color brick had no noticable impact on the image.

The leftover color was in the 2 - 5 degree hue range. It was mostly the red channel that was blown out on the histogram.

It would be nice to know what the color brick is doing but I suppose that's part of the "secret sauce" of Aperture.

A fun experiment, if I had the time, would be to try an image of a color wheel and play around with the Color brick's controls on it. How do you get an overexposed color wheel?

Now we've gone way off the reservation on this topic.