Noob question about ofPixels

jeromeh · June 18, 2016, 3:57pm

I’m trying to get the color from an ofPixels object

ofPixels camPixels = cam.getPixels(); ofColor col = camPixels.getColor(x,y);

It works but I get this error in the log?

[warning] returning color not supported yet for UNKOWN format
[ error ] ofPixels: format doesn’t support channels

roymacdonald · June 19, 2016, 6:45pm

Hi, it seems that you are getting an unknown pixel type from your camera. Which camera are you using? are you using with it an addon? the pixel type of the ofPixels object that the cam object returns has an unknown pixel type which finally leads to the crash.
you could also access the raw pixel data and extract color info from there.

camPixels.getData()

jeromeh · June 20, 2016, 10:46am

Hi, I’m using the cam from my MacBook

No addons.

roymacdonald · June 20, 2016, 2:39pm

Did you try the included examples?
OFFolder/examples/video/videoGrabberExample
OFFolder/examples/video/asciiVideoExample

if these work then you have a problem in your code.

Best

jeromeh · June 23, 2016, 2:20pm

Ok, it seems like it was due to the allocation … I used OF_IMAGE_COLOR and apparently it has to be OF_PIXELS_RGB?

I’m a bit confused by all the different modes possible there …

roymacdonald · June 23, 2016, 7:01pm

Why were you allocating the ofPixels object? that is done internally by the camera grabber.
Are you doing anything else with the ofPixels object anywhere else?

As of the confusion that you have, OF_IMAGE_COLOR is for ofImage objects and OF_PIXELS_RGB and is for ofPixels objects. It’s quite straight forwards. Although, the ofImage class contains an ofPixels instance, which might be what generates the confusion.
best

jeromeh · June 23, 2016, 7:53pm

OK, that makes sense, the IMAGE and the PIXELS … maybe COLOR and RGB confused me … anyway, oF is definitely much more complex and complicated than Processing! But yes, it’s also much more powerful.

Ah, ok, so I don’t need to allocate ofPixels in setup? Unlike ofTexture?

Usually I’m only loading ofPixels into a texture to draw it. But sometimes I need to get the pixels from it somewhere else in the code. But I’m still trying to figure out all the differences between ofPixels, ofTextures and ofImage …

roymacdonald · June 23, 2016, 8:28pm

Yes it is way much more powerful than processing.

If you are getting the ofPixels from somewhere else (like cam.getPixels()) theres no need to allocate them as you will get a copy of the pixels inside the cam object. Kind of the same goes for ofTextures.

take a look at this. It might be useful.

github.com

ofcourseio/SPRING2016/blob/master/week4/pixels.md

# Pixels
##### Author: Roy J. Macdonald


The pixel, short for **pic**ture **el**ement, is the smallest unit from which electronic images are made of. Each pixel contains information about a single color on a certain location on an image. There are modes for storing this color information. The most common modes are Grayscale (only grays, from black to white), RGB (Red, Green and Blue), RGBA (Red, Green, Blue and Alpha) or CMYK (Cyan, Magenta, Yellow and Black). Each of this values is stored as a number, and it is called a **channel.** Hence, Grayscale has 1 channel, RGB has 3 RGBA has 4 and CMYK has 4. The color information can be stored in any of these ways, but it will be needed to be transformed into RGB for electronic displays or CMYK for printing.

### Grayscale
The Grayscale pixel is the simplest one. I just has one channel and it only shows gray values, from black to white.

### RGB
In this mode the color information is stored as 3 different values (numbers), each corresponding to the amount of Red, Green and Blue needed to create the such color. Almost any color from the visible colors can be represented in this way.
This is the native mode that electronic displays use.
Electronic displays usually have pixels made of some material that can emit Red, Green and Blue colors independently on each pixel. Each of this elements will emit light with the intensity that its corresponding pixel channel has. When lights of different colors are mixed is called **additive** mix. 

Most displays have pixels made from 3 -Red, Green and Blue- stacked elements. 
These are so small that we cant see them so their light gets mixed and we see it as a single colored pixel.

![image](imgs/rgb-screen.jpg)

This file has been truncated. show original

BTW, read it in github so it gets rendered correctly.

best