This is a tutorial on basic bitmap image editing.

Foreword and introduction

Ok you have this image. You think it would look great (on a Wikipedia page), but it's not quite perfect. Perhaps it's too dark, or too big. If only you could clean it up a bit it would look great. Have no fear. This tutorial will show you a few tricks to turn an OK image into a thing of beauty.

Getting started

The first thing to do is open up an image-editing program. There are several possibilities.

For the rest of this tutorial, we will be describing how to use Paint Shop Pro to perform some simple image manipulations.

Irfanview: Resizing and cropping

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Select the Image menu. Then select "Resize/Resample".

Irfanview: Adjusting parameters (color, brightness etc.)

This has the purpose of "realistic" appearance (by default)

Some images can be color reduced (the color depth), even with a result in increasing "subjective" quality.
Others do not take color reduction well, or the filesize increases above that of JPEG.
Try to modify parameters in this sequence: First the Saturation, then Contrast, then Gamma factor, then R/G/B intensity. Adjusting Brightness easily gives unrealistic results.
It is possible to operate these factors artistically, but most likely a "normal" image should be archieved. This means how it would like to appear in daylight at 12pm, or under standard office light. Too bright images can disappear completely on some monitors. Generally different monitors can cause a change of 50 percent, there is never "exact" reproduction. In case of doubt, test the image file on different computers.

Select the Image menu. Then select "Enhace colors".

Irfanview: Choosing a Save file format

JPEG has become standard. However it is a lossy format, you should always keep a master file in a lossless format.
Reduction of quality to 85, 80, even 70 does not bug most images too much. However some can become quite ugly, and require high quality.
PNG requires more storage space. However, if the color depth is reduced, below 256 and even downwards to 5 unique colors, it sometimes outperforms JPEG! It is worth trying to save in different formats, and to carefully examine the results, compare versions in different JPEG quality next to each other on the screen.

Go to "File/Save as..

The image is too big

Sometimes an image is so large it dominates the page. As a general rule, images should not be more than about 300 pixels wide. The image that you see on the right would be over 500 pixels wide if it were simply to be uploaded. There are several things that can be done about a very large image. If it is a scanned image, it can be rescanned at a lower resolution. If however the image is digital it must be either resized or cropped.

Resizing

Select Image then Resize. You then get to choose the size of the image you want. Take care when resizing. The only way to make an image smaller is to throw away some of the pixels. If the image contains text, the pixels that get thrown away are not necessarily the ones that a human being would choose. If the top few pixels of the letter d are lost it becomes an a. Sometimes the only way to render readable, resized, text is to use the magnifying glass to look really close up, then pick up the correct colour with the dropper (the button that looks like a pipette), and finally select a one pixel paint brush to paint the letters in a pixel at a time.(The size of the paint brush can be adjusted from the style bar, which can be found on the view menu).

Cropping

If only part of the image is needed, it can be easily cropped. Use the selection tool to select the area that is wanted (see Fig.1) then copy and paste as a new image.

The image is dark or the color is wrong

The image looks to bright or too dark it can be adjusted by clicking on color then adjust then selecting brightness/contrast. A box pops up (fig. 2) with a small window that allows you to see the effect that any changes will have. Color can be adjusted similarly by selecting red/green/blue instead of brightness/contrast.

There is a tree growing out of someone's head

Well not literally perhaps, but often there are parts of the image that you would prefer are not there. The trouble is if you simply delete them with the eraser tool, you'll end up with a great big splodge of the background colour. What you would like to do is remove the offending tree but leave the sky alone.

Using the clone tool to erase offending objects

The clone tool (the button with two brushes) copies one area of the picture to another. To use it, you first right click the area you want to copy from, then left click and drag the area you want to copy to. A black cross appears on the picture to show you where you are copying from. Press and hold shift while rolling the while to adjust the width of the brush. On the picture on the right, you can see the tree is being erased by copying a portion of the sky over the tree.

See also