Photoshop founders Thomas and John Knoll

Adobe Systems' Photoshop software turns 20 years old on Friday.

Photoshop got its start in 1987 when Thomas Knoll wrote software that could display grayscale images--those with a range of gray tones--on monitors that could show only black or white pixels. He and his brother, John Knoll, licensed the software to Barneyscan in 1988, then to Adobe in 1989. Adobe Photoshop 1.0 arrived in 1990, and in 1995, Adobe acquired Photoshop outright from the Knoll brothers.

Thomas Knoll (left) still works at Adobe. John Knoll (right) is a visual effects supervisor at Industrial Light and Magic, where he worked on effects in several Star Wars movies, three Pirates of the Caribbean movies, and Avatar.

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Photo by: Adobe Systems / Caption by:

Photoshop 1.0

Adobe Photoshop 1.0 arrived in 1990, including tools such as levels and curves for adjusting tonality and the clone tool for copying one part of an image to another.

In 1991, Photoshop 2.0 debuted paths and the pen tool, mechanisms for isolating images that proved useful in publishing. In a move that would be nearly unthinkable today, the box art for Photoshop 2.0 didn't change.

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Photoshop 3.0

In 1993, the same year Microsoft Windows 3.1 arrived, Photoshop came to Windows with version 2.5. Adobe also released Photoshop 2.5 for two versions of Unix, Sun Microsystems' Solaris, and SGI's Irix, but later discontinued them.

Photoshop 3.0 in 1994 marked the arrival of layers, which let separate elements of an image be stacked for other, more sophisticated elements.

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Photoshop 7.0

Photoshop 7.0 was the last version with its own number. After it came the Creative Suite series, CS, CS2, CS3, and the current CS4. CS5 is expected later this year.

One important feature to arrive with Photoshop 7.0 was the ability to edit high-quality but unwieldy "raw" images taken directly from a camera's image sensor. The Adobe Camera Raw plug-in was a constant work in progress, updated to support new proprietary formats and expanding with new adjustment options.

Photoshop 7.0 also brought the healing brush, a feature that greatly eased the removal of age spots, wrinkles, and unsightly blemishes.
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Photoshop CS2

With Photoshop CS2, the healing brush was updated to the more automated spot healing brush, and photographers got a number of new abilities: corrections for lens distortion, quicker red-eye removal, a more elaborate sharpening module than the ages-old unsharp mask, and image warp for tasks such as slimming models.
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Photoshopping the news

Slimmer models in ads is one thing, but image manipulation also let a photographer exaggerate smoke from a bombing in Lebanon. That was unacceptable to Reuters, which yanked the photo and said it wouldn't accept any others from the photographer. The copying is most evident in the smoke to the upper right.

Image manipulation existed long before Photoshop, of course, but software makes the process that much easier. This photo is from Hany Farid's collection of images showing photo-tampering throughout history.

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Photo by: Hany Farid/Dartmouth / Caption by:

Lightroom arrives

The most dramatic departure in the Photoshop product is Lightroom. This software is dedicated to handling raw images, with all their advantages and drawbacks, though it will accommodate other formats as well.

Thomas Knoll, the original Photoshop programmer, also was an engineer on the Lightroom project, code-named Shadowland. Mark Hamburg initiated it.

Adobe used a much more open beta testing and feedback process for Lightroom than it had with Photoshop. It was beat to the market by Apple's conceptually similar Aperture, though.

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Photoshop tools

The toolstrip traditionally on the left edge of the Photoshop interface has changed gradually over the last 20 years. The tools are more complex than they appear: In the newer versions of the software, the small triangles by each icon lead to pop-up menus with several sub-options.
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Future Photoshop features

New versions of Photoshop are under way, and one feature that can be expected is a newly automated selection tool. Isolating subjects from their backgrounds is challenging even with simple images, but complicated elements such as hair make it even worse. This example, taken from an Adobe sneak peak, shows new automation for selecting a cat.
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Medical niche

Photoshop has several niche uses, including medical analysis such as this X-ray image. To help accommodate some of these areas, Adobe introduced its more expensive Photoshop Extended version starting with CS3.
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Submenus galore

In Photoshop CS4, tool icons have a multitude of options. Adobe is evaluating ways to clean up Photoshop's sprawling interface, which also has many panels, menus, and submenus.
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The eyes have it

For most of its history, Photoshop's icon prominently featured an eye.
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Photoshop 1.0 splash screen

Photoshop 1.0 was designed to work on monochrome monitors that could display only black or white pixels. The splash reflects the reality of digital imaging at the time.
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Photo by: Adobe Systems/Jeff Schewe / Caption by:

Stonehenge

Photoshop CS4 was code-named Stonehenge, and this splash screen shows through an Easter egg in the software.

Among other Photoshop code names: version 2.5 for Mac was Merlin and for Windows was Brimstone; version 3.0 was Tiger Mountain; version 4.0 was Big Electric Cat; version 5.0 was Strange Cargo; version 6.0 was Venus in Furs; version 7.0 was Liquid Sky; Photoshop CS was Dark Matter; CS2 was Space Monkey; and CS3 was Red Pill.

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Photo by: Screenshot by Stephen Shankland/CNET / Caption by:
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