User talk:Jacobolus/Archive 2011

CMYK color model

You seem to be the person responsible for the current appearance of the four colors C, M, Y and K in this article. I really don't think the blue in this illustration looks green enough to be cyan. If you look here you'll see what I mean.Vchimpanzee · talk · contributions · 15:59, 31 March 2011 (UTC)

Have you ever tried printing a 100% cyan on a CMYK printer? The color used in the diagram comes from numbers straight out a standard CMYK color profile. –jacobolus (t) 20:06, 31 March 2011 (UTC)

I have to admit I haven't, and I read what it said, but I have a difficult time believing it. I wanted to see what the actual color looked like onscreen, but Wikipedia apparently won't do that. I have to settle for those dots or squares in my newspaper.Vchimpanzee · talk · contributions · 20:09, 31 March 2011 (UTC)

The color shown in the diagram is about as close to the "actual color" as you can get on a computer display. I'm not sure what you mean by “Wikipedia won’t do that.” The “web color” “cyan” has nothing to do with the printing color, and only shares the name because whoever originally assigned names for web colors was horribly sloppy about it. –jacobolus (t) 10:07, 1 April 2011 (UTC)

When I say "Wikipedia won't do that" I mean a computer display. And the "actual color" is shown in that linkabove, on Wapcaplet's talk page. At least according to the article I got it from. I put them side by side for comparison. Actually, Wapcaplet's interpretation was completley diofferent.18:12, 1 April 2011 (UTC)Vchimpanzee · talk · contributions ·

We’re talking about this image, right? [to the right] It has the correct colors. This is as about as good as an sRGB display can show process cyan. –jacobolus (t) 19:28, 1 April 2011 (UTC)

But isn't this infobox supposed to be the same?Vchimpanzee · talk · contributions · 19:40, 1 April 2011 (UTC)

They are quite similar. Feel free to change the infobox if you want though. The source given doesn't remotely live up to WP:RS, and gives no explanation of how the coordinates were arrived at as far as I can tell. –jacobolus (t) 19:47, 1 April 2011 (UTC)

No thanks. What I'll do is go to a library that I know has color printing and see if they'll print out the two images for me. If one looks like the cyan in the newspaper, that'll settle it. But there's no way that CMYK box has cyan in it. It's not the least bit green.Vchimpanzee · talk · contributions · 19:52, 1 April 2011 (UTC)

Some landmarks shown on a plot of hue vs. value in the Munsell color system

That won't work. These are RGB images, and the printer won’t print them using purely its cyan ink. In any event, you’re confused about what “cyan” means. It doesn’t mean anything like “halfway between blue and green”, etc. What it means is “the greenish-blue color of ink used in a 4-color printing process.” Every particular printer is going to have its own “cyan” color, depending on what the chemistry is of the ink it uses. This picture to the right might be helpful. –jacobolus (t) 21:11, 2 April 2011 (UTC)

I knew what cyan meant. What I didn't know is what specific color it was. I thought the color that appears in the newspaper--on blue dot, one pink dot, one yellow dot and one black dot--was the same color used in all four-color printing processes, and that it would be a standard color that could appear onscreen. Now you're telling me each printer has its own.

Since I first asked you about this I have discovered the Talk:CMYK color model and that goes into unbelievable detail, which isn't helping either.Vchimpanzee · talk · contributions · 18:39, 4 April 2011 (UTC)

I will say the illustration on the right is pretty.Vchimpanzee · talk · contributions · 18:53, 4 April 2011 (UTC)

So just to further explain the illustration, the triangle at high lightness and right about at what might be called “blue–green” hue is the sRGB color (0% red, 100% green, 100% blue), which is the web color “cyan”, but this color is not really that close to the middle-lightness “greenish-blue” hue plus sign, square, and "x" symbols, which represent the cyan ink from three of the most common CMYK standard color profiles. As you can see, the CMYK cyan is quite different from the RGB “cyan”. Personally, I think any color in that “greenish blue” hue region (labeled gB) could be somewhat reasonably called “cyan”, but when I hear the word “cyan” I first think of the colors clustered around those CMYK ink colors. –jacobolus (t) 21:58, 4 April 2011 (UTC)

I think this is the cyan I'm looking for.Vchimpanzee · talk · contributions · 16:05, 5 April 2011 (UTC)

That’s pretty close in color to this one, just slightly lighter. CMY inks are outside of the gamut of RGB, so depending on how gamut mapping is done, you can get some variation in RGB approximation. That image you just linked had colors chosen by me myself, by using Photoshop’s default gamut mapping SWOPv2 to sRGB. –jacobolus (t) 19:19, 5 April 2011 (UTC)

This is weird. Sometimes what I linked to looks greenish and sometimes it doesn't.Vchimpanzee · talk · contributions · 19:36, 6 April 2011 (UTC)

File:Fire-breather CIELAB L*.jpg

On the HSL_and_HSV page you have extracted various lightness components for the Fire-breather image. It appears to me that the image you have shown for CIELAB L* is incorrect. After some investigation I think that the image was computed by using Rec. 708 equation 0.2126*R + 0.7152*G + 0.0722*B, except that it was used with the gamma-compressed (R'G'B') components instead of the linear RGB components. The actual image should be much darker and look significantly different from the Luma version. Yahastu (talk) 03:52, 4 May 2011 (UTC)

It’s maybe slightly tricky to call it L*, though I think the label is reasonable. The image is necessarily an sRGB image, because JPEG doesn’t support CIELAB space. So what it shows is a grayscale sRGB image in which each pixel has the same L* as the corresponding pixel in the original image. What you thought I was trying to create was instead a file wherein the pixels literally took on the values of L* in the original image; this of course would appear different (than both the image linked above and the original color image), because L* and the sRGB gamma function are somewhat different.

Because L* is a bijective function of luminance Y, it would be equally valid to say that each pixel in the resulting sRGB image has the same Y values as the corresponding pixel in the original. There might be some way of describing exactly what is shown that wouldn’t lead to potential confusion, but to be honest I can’t think of one: indeed all the alternative captions I can think of are likely to increase confusion. What I’m trying to show is that using L* as a lightness dimension better preserves perceived lightness relationships between colors than using one of the other dimensions described.

If you compare the “Luma” and “L*” images, you’ll notice that they are substantially different in highly saturated regions like the man’s face and clothes.

Hope that helps, jacobolus (t) 09:18, 4 May 2011 (UTC)

So to clarify, you first extracted the raw gamma-compressed R'G'B' from the color JPEG, then decoded the gamma to get linear RGB, then computed luminance as per. Rec. 708 above, and then re-encoded the gamma before saving as a grayscale JPEG, correct? Yahastu (talk) 13:58, 4 May 2011 (UTC)

I think actually what I did is took a file into Photoshop, converted to CIELAB, stipped out the a* and b* channels, and converted back to sRGB. But that basically amounts to the same thing as taking the sRGB file, decoding the gamma, adding the weighted components together, and then re-gamma-encoding. –jacobolus (t) 20:45, 4 May 2011 (UTC)

File source problem with File:Dorothea Lange pledge of allegiance.jpg

I noticed that the file's description page currently doesn't specify who created the content, so the copyright status is unclear. Sfan00 IMG (talk) 11:30, 5 May 2011 (UTC)

You provided a source, but it is difficult for other users to examine the copyright status of the image because the source is incomplete. Please consider clarifying the exact source so that the copyright status may be checked more easily. Sfan00 IMG (talk) 13:26, 5 May 2011 (UTC)

I answered on your talk page. –jacobolus (t) 21:24, 5 May 2011 (UTC)

Gamma correction image

I noticed that you reverted my image on the Gamma correction page. Your comment, "the new image is much uglier, and renders poorly" is not exactly forthcoming as to the problem with the image. I spent considerable time and effort ensuring that the new image would match the old one very closely. With the exception of the choice of font (which is beyond my control, as it is an SVG image), I'm interested to know what in particular is "much uglier" and "renders poorly" about it? Korval (talk) 04:44, 6 May 2011 (UTC)

Sorry, I should have phrased that more nicely. Yes, it’s just the font that’s uglier: the SVG file uses helvetica, but Mediawiki apparently won’t render Helvetica, and whatever it chooses as an alternative is awful. I'll try to cook up an alternative right now. –jacobolus (t) 05:47, 6 May 2011 (UTC)

So, why is my CMYK image worse?

I'm sorry but my image illustrating CMYK is undeniably better. Care to explain why you removed it? --Capsoul (talk) 21:00, 8 June 2011 (UTC)

Because the colors you used are 100% combinations of RGB primaries, rather than having any relation to CMYK. –jacobolus (t) 21:45, 8 June 2011 (UTC)

A question of color

Hi, you seem to be one of the color experts around here. BTW, I read the entire exchange at the Flag talk page which may or may not have been spurred by a question I asked here, but I did not read the exchange until just now.

One of my interests is sports teams, and I thought it would be useful to have a page with the official colors of sports teams. My interest is primarily college, but if anything came of this, there are obvious extensions to pro teams, both in the US and worldwide.

Frankly, I expected to find one, and I was surprised not to find one.

Then I assumed that I would find one on the internet is not at Wikipedia. Again, color me surprised that I couldn't find one easily. (I did find this but it fails on two important counts)

I'm writing to you for a few reasons:

• You know a lot more than I do about colors (although I do know what Cable Colors are, unlike some people)
• If there already is a Wikipedia article containing the info I want, you are very likely to know about it.
• If there's a resource on the internet with the information, you might already know about it, or be better equipped to know how to look for it
• If the project needs to be done, you are in a good position to provide useful advice.

My intention was to have an article (or multiple) about pro teams, and a separate one about college teams.

Within each article, I intended to provide a table showing the name of the school, the colors in familiar terms (e.g. red and white), then RGB values, CMYK values, Hex values, Pantone (possibly) and possibly HSL and/or HSV values. Finally, I want sources for each.

Here's where Colorwerx fails doubly. It is very comprehensive in terms of ordinary names for colors, but it has no conversion to any of the color spaces, and it has no sources. It may or may not qualify as a reliable Source, but I'd prefer to simply use it as a check.

(I'll omit, for the present, an additional dimension—time. One ought to specify a time range for each color, so that the list could be queried for any point in time to determine the colors at that time.)

I'd like, if possible to avoid the issues with s RGB, which I don't totally follow, so this may convince you I'm not entirely serious about this, but my hope is that one can specify the colors as mention above without delving into that issue.

Any feedback would be appreciated.--SPhilbrickT 00:21, 6 July 2011 (UTC)

Hi. I don't think CMYK, "hex", HSL/HSV are especially useful. You probably want to have the closest approximation in sRGB (the standard color space used on the internet, used as a target by many consumer devices), and more importantly the color in terms of a space like CIELAB, which has a clear “objective” meaning. –jacobolus (t) 08:57, 14 July 2011 (UTC)

Speedy deletion nomination of File:Sanzio 01 Euclid.jpg

A tag has been placed on File:Sanzio 01 Euclid.jpg requesting that it be speedily deleted from Wikipedia. This has been done under section F2 of the criteria for speedy deletion, because it is an image page for a missing or corrupt image or an empty image description page for a Commons-hosted image. Sfan00 IMG (talk) 11:36, 16 September 2011 (UTC)

That was speedy. –jacobolus (t) 13:25, 16 September 2011 (UTC)