CS 426 Assignment 2

An Image Enhancer

Due 11:59 PM, Friday, October 18, 1996

Introduction

For example, gamma will give you nine selections of various gamma settings to choose from. The original image will be shown at the top of the screen. When you select an image, it will move to the center and nine new choices will be presented. The choices to the left and right of the current choice will be only slightly different from the current one with the top and bottom rows moving more quickly away from the original one. Thus repeated choices should allow you to fully explore the space of possible transforms. This can continue until a new transformation type is selected.

Setting up

You can already see a fully working version of the program by running
tkenhance rex.ppm from your directory.

When you start programming, change the first line of the tkenhance script to make it point to your "imgwish".

How it works

Your job will be to fill in the various image processing functions, throughout the .c files. Whenever you see the string WORK HERE, you will have some work to do.

When you type make, you'll be building a program called imgwish, which contains all the usual Tcl/Tk stuff plus extensions for your image filters. tkenhance is a wish script for imgwish.

Each time a new transformation type is selected an entry will be made in a list of transformations. An image script of the chosen transforms and parameters can be written, which can actually be used later to apply your group of filters to a number of images from the command line.

You should try to make the code as efficient as you can. Think about operations that are used repeatedly, etc. For example, consider bitwise operations for the quantization, etc.

You will also have to submit 5 image scripts (.imgsh). These will be used to see how your filters can work together to produce your final artwork.

What to implement

• Add Noise (Continuous): Add noise to image.
  File: imgNoise.c

• Quantize (Enumerated): This one should produce a quantized image from 1 bit per channel to 8 bits.
  File: imgQuantize.c

• Dither (Enumerated):
  • 1 bit, B&W, 0.5 threshold.
  • 1 bit, B&W, random dither.
  • 1 bit, B&W, Bayer's 4x4 pattern dither.
  • 1 bit, B&W, Floyd-Steinberg error diffusion.
  • 3 bit, RGB, 0.5 threshold.
  • 3 bit, RGB, random dither.
  • 3 bit, RGB, Bayer's 4x4 pattern dither.
  • 3 bit, RGB, Floyd-Steinberg error diffusion.
  File: imgDither.c

• Gamma (Continuous):
  Adjust Gamma from 0 to less than 1 for darkening, 1 does nothing, and greater than 1 to 4 for brightening.
  out = in ^ 1/gamma
  File: imgGamma.c

• Brightness (Continuous): Adjust brightness from 0 (black) to 1 (original image). Values greater than one brighten the image.
  File: imgBrightness.c

• Contrast (Continuous):
  In the Img_ContrastFrom() function, you should compute the average luminance of your input picture. Then, interpolate/extrapolate from that to your original image. When the value is zero, you should get a constant grey. When it's one, you get the original image.

  Compare your Gamma, Brightness, and Contrast filters. Can you see the difference? What does it mean in each case when the filter's value is less than zero or greater than one? Note: Write the answer to these questions in your README file.
  File: imgContrast.c

• Saturation and Sharpening (Continuous):
  Extend what you've done in the previous example to do saturation and sharpening of images. The saturation filter needs to pre-compute a luminance image from the original picture and interpolate between that and the original image. The sharpen filter needs to pre-compute a blurry image from the original picture. You may want to experiment with different convolution kernels for different ways of blurring the original image.
  Files: imgSaturation.c and imgSharpen.c

• Fun 1 through Fun 4:
  You're required to implement two fun filters which can do anything you want. You should probably experiment with making the resulting pixel a function of more than just the original pixel at the same coordinate. Try different warping functions. Also, as you implement your filters, you'll occasionally get some spectacularly wrong results. You may wish to save those and submit them as ``fun'' filters. If it looks visually interesting, it can't be all bad.
  Files: imgFun1.c through imgFun4.c

File formats

You can convert a ppm to a gif file like so:
ppmquant 256 me.ppm | ppmtogif -interlace > me.gif

You can convert a ppm to a jpeg image like so:
cjpeg me.ppm > me.jpg
If your system doesn't have cjpeg, you can also view your picture with xv and save as a jpeg.

What to submit

When you're all done, you should have five image scripts and some number of favourite warped, distorted, and disfigured images. Choose two (or more) you like best, put them on a web page, and mention the URL for them in a README file which you submit with your assignment. We'll put our favourites on the class Web page.

Please submit:

• All .c and .h files
• makefile
• tkenhance
• a README file with the answers to the questions asked above, a description of your fun filters, and URLs pointing to some of your favourite pictures
• five .imgsh scripts generated by File -> Write Script...

Please don't submit binaries, images, or core files.