<p>Caveat: I know very little about the structure of digital images.</p>

<p>Assuming you mean the biological retina and not the prosthetic one, the Wikipedia page on <a href="http://en.wikipedia.org/wiki/Opponent_process" rel="nofollow noreferrer">color opponent process</a> is quite good; basically, the four receptor types respond maximally to different wavelengths, and the ranges overlap slightly, so the visual cortex does the differences between the activation levels to get a complex representation of color.  </p>

<p><img src="https://i.sstatic.net/tmKEk.png" alt="Opponent processing"></p>

<p>In terms of where in the visual field (pixels vs "shapes"), again, <a href="http://en.wikipedia.org/wiki/Receptive_field#Retinal_ganglion_cells" rel="nofollow noreferrer">retinal ganglion cells</a> have what is called a receptive field--they respond maximally to stuff in the middle and less so to stuff on the periphery (whether "stuff" is light or shadow depends on their exact type).  So although the spatial definition of a "pixel" is a bit more complicated in the retina than in a bitmap, and simplifying grossly. . . <strong>it's more like a bitmap</strong>, I think.  There's no edge processing or shape definition at the retinal level--there's no "processing" at all in the retina, just transmission--so vector-type processing doesn't happen until visual cortex.</p>

CC BY-SA 3.0
2015-02-12T03:37:21.497Z
There is edge enhancement in the retina, among other neural processing mechanisms. But I agree that when choosing between a vector image and bitmap, the retina is a bitmap, but it is a gross oversimplification. +1
AliceD
CC BY-SA 3.0
2015-02-12T11:34:00.987Z
@ChrisStronks Can you say more about image *processing* in the retina?  I had always understood that there was image/shape/edge transmission, but no information convergence between different sensor types or receptive fields such as happens further downstream.  Not sure if we are working off of different definitions of image processing or if you have more information, but very curious!
Krysta
CC BY-SA 3.0
2015-02-11T20:52:47.883Z
2015-02-11T20:52:47.883Z
Krysta
<p><strong>Short answer</strong><br>
The retinal image corresponds more to a bitmap, than a vector-based image</p>

<p><strong>Background</strong><br>
The retina contains a layer of about <a href="http://www.britannica.com/EBchecked/topic/458127/photoreception" rel="nofollow noreferrer">100 million photoreceptors</a> that are <strong>topographically</strong> organized. In other words, each <strong>photoreceptor</strong> codes <strong>one specific pixel in the field of view</strong>. In turn, the nerve fibers running from the eye to the brain are also topographically organized in the same way the retina is (<em>retinotopy</em> is maintained up until the higher brain centers and is lost only in the inferotemporal cortex). Hence, yes, basically, but grossly oversimplified I agree with @Krysta that the <strong>retinal image more closely corresponds to a bitmap</strong> than a vector-based image. Nonetheless, colors, contrasts and edges are coded in the retina. </p>

<p>Here is a picture on retinotopy. Basically a 1:1 topographic representation of the retina can be found in the primary visual visual cortex:<br>
<img src="https://i.sstatic.net/cxoTu.png" alt="retinotopy"><br>
<sup>source: <a href="http://www.britannica.com/EBchecked/topic/458127/photoreception" rel="nofollow noreferrer">University of Leeds and Sydney</a></sup></p>

<p><strong>Retinal implants</strong> are devices that <strong>replace the lost photoreceptors</strong> in the retina in patients with <em>retinitis pigmentosa</em> or other retinal degenerative diseases. Retinal implants typically consist of a <strong>grid of electrodes</strong> (60 - about 1500 in commercially available systems) that are placed on (Argus II) or below the retina (alpha-IMS). </p>

<p>Here's a fundus photo of an Argus II implant:</p>

<p><img src="https://i.sstatic.net/I5DB0.jpg" alt="Argus II"></p>

<p>The electrodes directly <strong>stimulate the surviving neruonal cells in the retina</strong>. Retinal implants make use of the retinotopy. An electrode in the center of the retina will elicit a spot of light (a <em>phosphene</em>) in the central fielfd of view, whereas a more peripherally situated electrode will generate phosphenes more eccentrically. Hence, camera images (in the Argus II device) are simply <strong>downsampled</strong> and projected onto the electrode grid as <strong>intensity-coded stimuli</strong>. In the alpha-IMS system the intra-ocular part consists of a grid of photosensitive diodes coupled to small amplifiers. Hence, in this device it is, quite literally, a photosensitive chip thrown on the retina. In both approaches, brighter areas in the image receive higher electric currents and result in brighter and/or larger percepts.  </p>

<p><sup><strong>Reference</strong></sup><br>
<sup><a href="http://informahealthcare.com/doi/abs/10.1586/17434440.2014.862494?journalCode=erd" rel="nofollow noreferrer">Stronks et al. <em>Exp Rev Med Dev</em>;<strong>11</strong>:23-30</a></sup></p>

CC BY-SA 3.0
2015-02-12T20:28:40.233Z
Wow, both really high-quality answers. This is really cool, thanks. It seems then that it's a bitmap with some svg edges overlayed?
John
CC BY-SA 3.0
2015-02-12T03:33:27.033Z
2015-02-12T23:27:06.293Z
2015-02-12T23:27:06.293Z
AliceD
<p>I heard recently that a scientist has developed a retina prosthesis. So I think this is a question that has an answer.</p>

<p>Does the retina encode information like a Bitmap image or an SVG image?</p>

<p>(A Bitmap is a grid of pixels. An SVG image is vector based, so that it defines a shape and says 'in this region, it's green, in that it's red', so to speak.)</p>

CC BY-SA 3.0
2015-02-14T20:16:04.403Z
The eye sends a Bitmap to the brain. The brain interprets it somewhat like a SVG where the brain only focuses on the relevant complex information structures in the image that you as a person chooses to focus on.
wesserbisser
<vision><neurophysiology>
Does the retina encode visual information like a Bitmap or an SVG?
John
# Does the retina encode visual information like a Bitmap or an SVG?

(Asked by: username_0 on 2015-02-11)

I heard recently that a scientist has developed a retina prosthesis. So I think this is a question that has an answer.

Does the retina encode information like a Bitmap image or an SVG image?

(A Bitmap is a grid of pixels. An SVG image is vector based, so that it defines a shape and says 'in this region, it's green, in that it's red', so to speak.)

**Tags:** vision, neurophysiology

> **Comments:**
> **username_1**: The eye sends a Bitmap to the brain. The brain interprets it somewhat like a SVG where the brain only focuses on the relevant complex information structures in the image that you as a person chooses to focus on.  

---

## 2 answers

### Answer by username_3 on 2015-02-12. Score: 6 | Accepted answer

**Short answer**  
The retinal image corresponds more to a bitmap, than a vector-based image

**Background**  
The retina contains a layer of about [100 million photoreceptors](http://www.britannica.com/EBchecked/topic/458127/photoreception) that are **topographically** organized. In other words, each **photoreceptor** codes **one specific pixel in the field of view**. In turn, the nerve fibers running from the eye to the brain are also topographically organized in the same way the retina is (*retinotopy* is maintained up until the higher brain centers and is lost only in the inferotemporal cortex). Hence, yes, basically, but grossly oversimplified I agree with @username_2 that the **retinal image more closely corresponds to a bitmap** than a vector-based image. Nonetheless, colors, contrasts and edges are coded in the retina.

Here is a picture on retinotopy. Basically a 1:1 topographic representation of the retina can be found in the primary visual visual cortex:  
![retinotopy](https://i.sstatic.net/cxoTu.png)  
source: [University of Leeds and Sydney](http://www.britannica.com/EBchecked/topic/458127/photoreception)

**Retinal implants** are devices that **replace the lost photoreceptors** in the retina in patients with *retinitis pigmentosa* or other retinal degenerative diseases. Retinal implants typically consist of a **grid of electrodes** (60 - about 1500 in commercially available systems) that are placed on (Argus II) or below the retina (alpha-IMS).

Here's a fundus photo of an Argus II implant:

![Argus II](https://i.sstatic.net/I5DB0.jpg)

The electrodes directly **stimulate the surviving neruonal cells in the retina**. Retinal implants make use of the retinotopy. An electrode in the center of the retina will elicit a spot of light (a *phosphene*) in the central fielfd of view, whereas a more peripherally situated electrode will generate phosphenes more eccentrically. Hence, camera images (in the Argus II device) are simply **downsampled** and projected onto the electrode grid as **intensity-coded stimuli**. In the alpha-IMS system the intra-ocular part consists of a grid of photosensitive diodes coupled to small amplifiers. Hence, in this device it is, quite literally, a photosensitive chip thrown on the retina. In both approaches, brighter areas in the image receive higher electric currents and result in brighter and/or larger percepts.

**Reference**  
[Stronks et al. *Exp Rev Med Dev*;**11**:23-30](http://informahealthcare.com/doi/abs/10.1586/17434440.2014.862494?journalCode=erd)

> **Comments:**
> **username_0**: Wow, both really high-quality answers. This is really cool, thanks. It seems then that it's a bitmap with some svg edges overlayed?  

---

### Answer by username_2 on 2015-02-11. Score: 5

Caveat: I know very little about the structure of digital images.

Assuming you mean the biological retina and not the prosthetic one, the Wikipedia page on [color opponent process](http://en.wikipedia.org/wiki/Opponent_process) is quite good; basically, the four receptor types respond maximally to different wavelengths, and the ranges overlap slightly, so the visual cortex does the differences between the activation levels to get a complex representation of color.

![Opponent processing](https://i.sstatic.net/tmKEk.png)

In terms of where in the visual field (pixels vs "shapes"), again, [retinal ganglion cells](http://en.wikipedia.org/wiki/Receptive_field#Retinal_ganglion_cells) have what is called a receptive field--they respond maximally to stuff in the middle and less so to stuff on the periphery (whether "stuff" is light or shadow depends on their exact type). So although the spatial definition of a "pixel" is a bit more complicated in the retina than in a bitmap, and simplifying grossly. . . **it's more like a bitmap**, I think. There's no edge processing or shape definition at the retinal level--there's no "processing" at all in the retina, just transmission--so vector-type processing doesn't happen until visual cortex.

> **Comments:**
> **username_3**: There is edge enhancement in the retina, among other neural processing mechanisms. But I agree that when choosing between a vector image and bitmap, the retina is a bitmap, but it is a gross oversimplification. +1  
> **username_2**: @ChrisStronks Can you say more about image *processing* in the retina?  I had always understood that there was image/shape/edge transmission, but no information convergence between different sensor types or receptive fields such as happens further downstream.  Not sure if we are working off of different definitions of image processing or if you have more information, but very curious!  

---

