Pixel-based images

Pixel-based images, also referred to as Raster graphics or Bitmaps a made up of small squares or dots known as pixels. A pixel (pixel-element) is the smallest editable element in a pixel-based image. A pixel-based image may be stored as a number of file formats such as a jpeg, png, gif, tiff or psd. Unlike Vector based imagery, pixel-based imagery is resolution dependent and can not be scaled up without loosing quality. Resolution is typically measured by the number of pixels per inch (ppi). The higher the number of pixels per inch the higher the image quality will be and the larger the file size will become. Each pixel in an image has a position on the document and an RGB value. By altering the RGB values and positions of various pixels in an image using a pixel editing program such as Adobe Photoshop, we can retouch and alter an image in a vast variety of ways. All digital photographs are pixel-based as are the majority of of images within a web page.

This video takes an imaginary journey into the land of the pixel:

Uploaded by onemoreprod. – Watch original web videos.

“Warm Up” colour adjustment

  1. From the bottom of the Layers pallet choose the Create new fill or adjustment layer menu.
  2. Choose Levels
  3. Make a tonal adjustment by bringing the highlight and shadow sliders to the ends of the histogram. Adjust the midtone slider to set the desired brightness.
  4. In the Layers pallet choose Red from the channel menu.
  5. Slide the midtone slider to the left until the image appears noticeably red.  Let your eyes adjust to the colour for a moment then ease back the slider until the image does not look noticeably red anymore.
  6. Now choose Blue from the channel menu.
  7. Slide the midtone slider to the right until the image appears noticeably yellow.  Let your eyes adjust to the colour for a moment then ease back the slider until the image does not look noticeably yellow anymore.
  8. View the image before and after the adjustment by switching the visibility of the adjustnment onf and off. Make further adjustments as necessary. The image should not appear noticably red or yellow but should have a generally warmer appearance.

NOTE:  Most of the time the green channel will not need adjusting.


Image retouching with Photoshop

(See more “Celebrities Before and After Photoshop“)

The majority of images we see these days have had some level of digital alteration. It may be to simply correct the photographic aspects of the image (lighting, colour, sharpness, perspective etc) or may take the image to a level far beyond that which the camera captured. Although our image editing tools are much more sophisticated today, photographers have been altering their images since the early beginnings of the craft.

Digital image retouching with tools such a Adobe Photoshop allows us to elegantly alter every aspect of the image. From the simple removal of a blemish to a complete reconstruction of the bodily or facial form the original image captured by the camera can now take a radical and convincing departure.


This article from Smashing Magazine collects a large range of tutorials for techniques commonly used for Glamour Retouching. (Note the ethics discussion that ensues.)

This article in Inspired Magazine opens a discussion on the realities and ethics surrounding the practice.

This video from Adobe TV shows the basics of blemish retouching:

Understanding Resolution

The term resolution refers to to the amount of information in an image.
Devices such as digital cameras, printers, scanners & monitors all have a particular resolution.
Image resolution is measured by the amount of Pixels Per linear Inch (PPI) or Dots Per Inch (DPI) if referring to print resolution.
The more pixels per inch the higher the image quality (and the larger the file size will be) .
High quality print resolution is typically 300ppi. 300ppi is roughly the limit of what the human eye can distinguish.
Monitor resolution varies greatly depending on the device (from a 19ppi TV to a 340ppi mobile phone). Find the PPI of your monitor in this Wiki entry.
Unlike when printing, an image will be displayed on a monitor pixel to pixel so will change size depending on the devise.

Here’s a pretty simple breakdown of resolution.

Here’s a well written and relatively easy to grasp explanation.


Online photo editors

Whether you are away from your own machine or want to save money on expensive photo editing software there are some very powerful and free online tools to help you edit you photographs directly from the browser.

Kings of the road in this camp are Sumo Paint and Pixlr.  Both mimic Adobe Photoshop quite closely and offer some very sophisticated image editing and imaging making tools.



Picnik, recently acquired by google is clean and feature rich. Picnik seamlessly combines easy to use automated functions alongside some more advanced tools like a Histogram and an Unsharp Mask. Picnik is aimed at the general user and is mainly designed to prepare images for web based application. Most base features are free but some effects and tools are only available at a cost with the premium version.

Adobe has an online version of Photoshop called Photoshop Express that is perhaps a little more serious than Picnik. Here  we are presented with editing techniques that are a little more photographic in nature.

Both provide various options for output and upload to popular social media sites. Photoshop Express aims to incorporate itself as a social network by allowing you to share albums and view albums of other Photoshop Express users. Both are excellent tools suitable for beginner and advanced image editing.

Non Destructive Editing in Photoshop

This has become a real mantra for me when teaching. Photoshop by nature is quite a destructive application. It is easy to, in a few simple steps, irreversibly damage an digital image if we use Photoshop in the way that seems initially intuitive. Non Destructive Editing is a method of working in Photoshop that leaves the original image untouched and prevents us from progressive striping information from the digital file. Layers, Adjustment Layers and Layer Masks are key elements in this way of working.

Intuitive photo editing and management with Adobe Lightroom

Most people think Adobe Photoshop when they think about working with their digital photos. These days I spend most of my time using Adobe Lightroom for my photographic editing and management. It’s simple and intuitive, non destructive yet powerful and quick to move around in. I can perform most of what I ever want to do with my images in Lightroom and find myself only jumping to Photoshop these days if I need to montage images together or want to use it as a graphic design tool.

Apple’s Aperture software is a similar and equally sophisticated piece of software.