14.4 Video processing part 2: grayscale and color  (Page 2/3)

Example:

• int black = 0x00; // black = 0
• int foo_h = 0xF0; // foo_h = 240
• int foo_l = 0x0D; // foo_l = 13

Another thing to note is that each pixel requires two bytes of memory, requiring two memory access operations to alter each pixel. Also NOTE that in a row of input color data, the indexing starts at 1. Thus RGB[1] contains red/green data and then RGB[2]contains the green/blue data – both for the first pixel.

What is the packed RGB value for the highest intensity green? What is the value of the first addressable byte of this ‘hi-green’ pixel? What is the value of the second byte?

Now, say you are given the declaration of a pixel as follows:

int pixel;

Write a simple (one line is sufficient) section of code to add a blue tint to a pixel. Do the same for adding a red tint, and for a green tint (may require more than one line).Use the and (represented by an ampersand) operator to apply a mask.

Implementation

The first part of this lab will require you to write a function to perform auto-contrasting. You should use your function from prelab 2.1 to obtain the maximum and minimum values of the image, and then create another function to do the appropriate scaling.

The second part of this lab will involve implementing some simple, and hopefully cool, color effects.

Grayscale

Use the function you designed in prelab 2.1 to create an algorithm to auto-contrast the image. Auto-contrast is accomplished by scaling the pixel value from the min-to-max range to the full range. This effect is seen below:

Recall from “Introduction to the IDK” that the DSP has a floating point unit; the DSP will perform floating point instructions much faster than integer division, quare-root, etc.

Example:

• int opposite, adjacent;
• float tan;
• tan = ((float) opposite) / ((float) adjacent);

This function should be called similarly to the flip_invert function in the previous lab. Once you have implemented your function, look for ways to optimize it. Notice that you must loop through the image twice: once to find the minimum and maximum values, and then again to apply the scaling. (Hint: the function dstr_rewind rewinds the image buffer).

Use the same core files for this part of the lab as were used in the previous lab. You may simply make a copy of the previous lab’s folder and develop the necessary code from there.

Color

In this part of the lab, you will use the concepts from the prelab to implement certain effects.

Copy the directory “V:\ece320\projects\colorcool” to your W: drive.

We want to use a certain area of the screen as a "control surface". For example, the fingers held up on a hand placed within that area can be used as a parameter, to control the image on the screen. Specifically, we will use the total brightness of this control surface to control the color tint of the screen.

You are given a shell program which takes in a color input frame in YcbCr format and converts it to RGB. You will modify this shell to

• 1. Calculate the total brightness
• 2. Calculate the tint for each color component R, G and B.
• 3. Apply the tint to the image