Week 7: Image Lab 1

Manipulating images using arithmetic 

Image filtering, enhancement and general manipulation using Photoshop

1) Find the images on Moodle to be used in this lab and download on to your desktop.

2) Click on All Programs->AdobeCreativeSuite4ProductionPremium and run Adobe PhotoshopCS4

3) Use File\Open CH_Tor.jpg to display the image in Photoshop.

4) Perform Image->Image Rotation->90 degrees CW

5) Apply a custom filter to the image in the manner discussed in the lecture to filter the image as Filter->Other->Custom
Modify the default Mask to
    -1

-1  4 -1

    -1
What is the effect of the default mask? Why do you suppose that it creates the effect that you see?

The default mask seems to change the image to a black and white style. In doing so it highlights straight edges with white whilst solid blocks of colour seem to change into black. I'm not entirely sure why this is the output. I assume that the value of the pixels found in the straight lines is turned into a negative whilst the reverse is the case for large spaces of the same colour.

6) Experiment with various masks and explore the use of the preset masks in the High pass, maximum and minimum options. Where possible describe and explain what you see?

On the left is the Maximum Mask, the middle is the High Pass Mask and the right is the Minimum Pass Mask. The Maximum mask seems to be darkening/amplifying the darker colours in the tower. Whilst the lighter colours seemingly remain untouched. The Minimum mask does the opposite and lightens the lighter colours in the tower. For both filters the is most notable in the actual clock. The High Pass Mask is a little harder to explain. A glow is created around the main points of the image and everything seems to become a little foggy. The gradient blue in the back ground is now for the most part a solid grey. 

7) Suggest possible uses of this filter technique for processing digital photographs?

The most plausible use for any filter technique in terms of processing digital photographs would be to first and foremost improve the quality. Decrease pixilation, smooth edges that need smoothed and sharpen lines that need sharpened. Following touch ups another use would be to use the filters for additions and extras. Something to change the image for the better to make it stand out a little from the original.

8) Create a new filter that is all zeros except for the centre value which should be 1. What does this filter do and why?

How can you check that it operates as you think it does?

The mask seemingly doesn't change anything. The only way to check that this mask is operating as I think it has is to simply view both the original image and the image with the mask beside each other and by doing so I see no differences in the image.

9) Create a new filter with a two by two matrix of 1’s near it’s centre. What does this filter do and why?

This filter seems to dramatically brighten the colours. Although you can still see some examples of the darker textures. The sky being one of lighter colours in the image is now almost completely white. This is the effect of saturation.

10) Create a new filter with a two by two matrix with +1’s on one diagonal and –1’s on the other. What does this filter do and why?

This filter seems to be a much more extreme version of the find edge filter from before. As you can see the edges are now highlighted as white, very faintly against an incredibly dark shade for the rest of the image. Once again this is reversing the value of the pixels to accomplish this.

11) Some other filters and their effects:

On the right is the tower with an embossed style of filter applied to it. It seems to highlight the various shapes shown in the picture, notably the individual bricks in the building. The image on the left has been heavily sharpened and accomplishes a similar style of the embossed image.