How dogs see color

In behavioral tests with three dogs, Neitz, Geist and Jacobs (1989) found two classes of cone pigment, with peaks of about 429 nm and 555 nm, and concluded that dogs have dichromatic color vision. Human eyes have three cone types; in a human retina measured by Bowmaker and Dartnall (1980) they peak at about 420, 534 and 563 nm.

Jacobs and colleagues (1993) measured the same pair of cone pigments in dogs and three kinds of fox, about 555 nm and 430–435 nm, and placed the peak of the dog rod pigment at about 508 nm.

With one short-wave and one long-wave cone, colors that differ for us mainly in how red or green they are can give a dog the same signal. Blue against yellow stays clear. The table below runs a few everyday pairs through the same model as the simulator and gives the color difference (ΔE 2000) for a person and for the dog model: the smaller the number, the harder the pair is to tell apart. On the scale we use across this site, below 3 is a close match, 6 or more is a visibly different color, and 10 or more is clearly different.

The simulator is built from the dog's own cone peaks (429 and 555 nm). For each color it estimates how strongly it would excite each of the two cones, using the pigment template of Govardovskii and colleagues (2000) and daylight (CIE D65), and shows a color that excites them in the same way. The cone signals weigh the light by its energy; a cone counts photons, and weighting by photon count instead would shift some shown colors slightly, by up to about 7 of 255 in one color channel by our check. The shown colors lie on a yellow–blue axis plus lightness, the same plane that Viénot, Brettel and Mollon (1999) use for people with two cones, so colors that give the dog the same pair of cone signals come out identical. It is an approximation: the eye's lens is left out, each color's spectrum is a guess from its screen color, and the picture is blurred to the animal's visual acuity, as explained below. Everything runs on your device: the camera picture, photos and videos are not uploaded.

Color is not the only difference. Lind and colleagues (2017) trained whippets, pugs and a Shetland sheepdog to choose between a card with horizontal stripes and a card with vertical stripes, and made the stripes finer and finer; a dog's limit was the finest stripes it still picked correctly three times in four. Two of the pugs performed poorly, and the authors left them out of the analysis. In bright light the other six dogs resolved 5.5, 6.0, 6.7, 15.8, 17.4 and 19.5 cycles per degree (one cycle is a dark and a light stripe); people tested in the same set-up reached 32.1 to 44.2. In the authors' words, "humans make visual discrimination of objects from roughly a threefold distance compared to dogs".

The simulator blurs the picture to 6.7 cycles per degree, the lower of the two middle dogs (a whippet). That is a little above the 4 to 6.2 cycles per degree of an earlier behavioral test that the same paper lists, not inside it. The paper itself is titled "High visual acuity revealed in dogs". The sharpest dogs in the study, a pug and two whippets, resolved about 2.4 to 3 times finer detail than the simulator shows.

How the blur is made: the simulator follows AcuityView, the method of Caves and Johnsen (2018). Fine detail is faded along a bell-shaped curve that leaves about 3% of the contrast at the animal's acuity limit, and coarse shapes and colors stay. A picture does not say how wide the scene was, so the simulator assumes that the long side of the picture covers about 70°, the view of a typical phone's main camera (the iPhone 16 main camera is 26 mm in 35 mm terms, about 69° across). If you zoomed in or cropped, the scene was narrower and the animal would see it blurrier than shown. The blur stands for the sharpest part of the eye only; the rest of the animal's view is not modelled. On a phone screen the difference in sharpness is hard to see. Open full screen, or look at a large monitor, to notice it.

A review by Byosiere and colleagues (2018) points out how little is known about dog vision overall, and that the great variety of dog skulls and faces may change how different breeds see.

How well, compared with us, has not been measured. A dog's eye is built for dim light: Yamaue and colleagues (2015) counted 200,000 to 540,000 rods (the cells that work in dim light) per square millimetre of dog retina, and found the tapetum, the reflective layer behind the retina, thickest (9 to 12 cell layers) where the rods were densest.

We have not found a test that measured the dimmest light a dog can see, so we do not give a figure such as "five times better". Cats were tested: they detected large, coarse shapes in about 5 to 6 times dimmer light than people in the same task (Kang and colleagues, 2009). In our night mode the dog is drawn as sensitive to light as you.