Lecture Notes

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• color balance
• color inversion
• threshold

• filter
• perspective correction
• masks

• Image editing in Photoshop
• Photoshop makes it very easy to overcome image drawbacks such as:
• Overly dark or light images can be made better.
• The color balance can be adjusted.
• By selecting image…adjust…curves, one can easily adjust the color curves related to a given image.
• One can choose to edit the image in its entirty or on the basis of individual channels.
• The colors can be easily inverted.
• This is quite simply done by switching all values of the colors in the histogram to their extreme opposites.
• Threshold- by adjusting the threshold, one can remove marginal data.
• For example: if one sketches on yellow trace, then scans it, the splotchy result which one receives can be removed.
• Filters
• Examples of algorithms- small program within application to perform a task on image.
• Most effects result in blurring the original image.
• However, there is a sharpen filter which can clear up fuzzy edges between fields, for example.
• When on takes a photograph, often there is some perspectival distortion effecting the images which is produced, which before beginning an analysis, one my want to correct.
• This is quite simply because unless the shot was carefully lined up, the image which was taken, was most likely a two or three point perspective.
• In two point perspectives, 2 out of 3 of the x,y,z coordinates describing the relationship between the subject and the lens must be the same to result in a distortion free image.
• In a three point perspective, all three values must be the same.
• To correct perspectival distortion:
• Drag down guidelines to determine how skewed the image is.
• Under the edit menu, select free transform
• One can then select perspective, and alter the image in such a way that counters some of the distortion.
• To counter a misaligned image (due to camera rotation):
• Under the layer menu, select rotate canvas
• Next select arbitrary, then input the value and rotation desired.
• It is possible to remove unwanted objects from a composition.
• One can select a similar color, and paint over an object.
• However, this does not work well with textures, and regions with multiples colors.
• A more sophisticated method involves the rubber stamp tool.
• After selecting the tool, select from where you want to pick up pixels (this essentially copies those pixels from within the selection region. (Alt + click)
• Next, click where one wishes to place the new pixels
• Using masks
• Masks are simple ways to restrict which areas of the canvas ones operations will take effect.
• Using the marquee tool, select the area in which to work, the select the create mask tool.
• To edit the mask further, one can add to it by placing black on the canvas, or subtract from the mask by painting in white.
• While performing these operations, the user can view them as they are done, before they are applied.

This is why Photoshop requires so much memory to run smoothly; it is storing the original image, as well as the altered image.