Visual acuity redux

A visual acuity test (or something like it)” was prepared in conjunction with an essay on differences (I’d call it “discrimination” but that word’s been damaged) for the August Cites & Insights–and, sigh, I think I did the image wrong. There were supposed to be six rectangles on a pure-white background, with each rectangle differing by having one or two of the primary colors (RGB) reduced from #FF to #FE.

Somehow (still haven’t figured out how, unless JPEG is to blame) I wound up with only five colors–three of the six rectangles had the same color.

I did get some useful comments, including at least one person who apparently has extraordinary color acuity.

This time, I’ll give you the image and tell up front that there should be ten colors on it–nine off-white shades with two narrow bands of pure white between them. This time, I closed the file and reopened the JPEG version; Paint.NET’s color picker does show nine different values. If you’re like me, you may be able to see the bottom three rectangles if you look really hard. Some of you may see some of the center row.

This time, the top row should be one FD and two FFs; the center row was intended to be FCFFFF, FCFCFF, and FCFCFC respectively; the bottom row goes all the way down to FB for one of the three primaries in each box. I say “should be” and “intended to be” because reopening the JPEG version shows some shifts in the top two rows–still nine colors, but not precisely the nine I started out with.

Don’t think you can actually perceive 16 million colors? You may be right.

On the other hand, there are cases where–at least to my eyes–a one-digit change in one of the three primaries is visible if you put the two colors side by side. I have that example in the essay (which is mostly not about color acuity but about differentiation in general).

Anyway, here’s the ten-color image, for what it’s worth:


6 Responses to “Visual acuity redux”

  1. Kate W says:

    I could only see three in the last one but all 10 here. Power of persuasion? Or the order of them? I can see them better when I make the box smaller on my phone, and better still wearing my glasses than with contact lenses.

    I find this weirdly neat.

  2. Walt Crawford says:

    There were at most four in the last one. The differences in this figure are larger than in the other one–always at least two-digit changes, where the other one began with single-digit changes (where “digit” is a change of 1/256th of a primary color’s saturation).

    I also find it depends on the settings of a display–e.g., on my ancient Sony 19″ LCD display (at least 5 years old, and I think more like 7), I can barely distinguish three colors in “PC mode” but can sort of make out all ten in “movie” mode.

    I also find it weirdly neat. The August essay may be fun.

  3. Bill says:

    The test has little to do with visual acuity — it’s more of a test of colour discrimination. Being well on the way to colourblind myself, I can see nothing but undifferentiated “pale”. (To people like me, “dark” and “pale” are colours as much as colour categories.)

  4. Bill says:

    Update: my wife, who has perfect colour vision and some training as an artist, can see nothing but white either. She says our monitor is not coming with us when we move apartments next month. 🙂

  5. Walt Crawford says:

    Bill: Good point. It’s about discrimination or differentiation (I’m finding that “discrimination” is a hopeless word these days). And, of course, it’s not a test–just an amusement.

  6. laura says:

    Yeah, monitors clearly make the difference. On some monitors I see all 9 colors here; on others, none.