Apple has come under fire for its decision to demonstrate its new iPad Pro 'monster' tablet by photoshopping a model's smile.

The firm invited Adobe's Eric Snowden to show off the latest version of the image editing software, called Photoshop Fix.

Using the software, he manipulated a model's face to turn up the corners of her mouth, making her appear to smile more.

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Apple has come under fire for its decision to demonstrate its new iPad Pro tablet by manipulating a model's face into a smile. The firm invited Adobe's Eric Snowden to show off image editing software.

'I'm not quite happy with the model's smile, I wish she had more of a smile to warm up the layout - and luckily we have an app for that,' said Snowden.

Twitter erupted with angry and responses from event attendees and livestream viewers, and raised the question of diversity in the tech world.

'Did he really just force-Photoshop a woman to smile more at this Apple event? THAT was the best example of image editing...?' a user name Emily Combs tweeted.

'Oh thank god we've made the men of Apple feel more comfortable with her facial expression. PHEWWW,' another said .

Adobe's Scott Benskey took to Twitter to defend the firm.

'I know team never meant for photoshop demo to be offensive,' he said.

'#1 use of retouch apps is for selfies, intention was to show off the tech.'

The app was shown off to highlight the processing power of the new giant iPad Pro

Apple featured three female presenters on stage, more than it has in the past, but only one of them was an employee, Jen Folse, who introduced Apple TV.

The other two presenters, Irene Walsh and Michelle Peluso, represented some of Apple's partners.

Walsh is the head of design at a medical software company, 3D4Medical. Peluso is CEO of shopping site Gilt Groupe.

Yeah, make that woman smile, Apple pic.twitter.com/WlsNpHa9qC — Damon Beres (@dlberes) September 9, 2015

how did someone at Apple OR Adobe not think through the optics of a dude "fixing" a woman's smile? — Beth Carpenter (@bethshanna) September 9, 2015

Big companies like Apple, Facebook, and Microsoft have started publishing their gender and diversity numbers, promised to hire and promote more women and minorities, and put a lot of money toward national education programs.

Adobe's Eric Snowden showing off the latest version of the image editing software Photoshop on the iPad Pro, which came under fire on Twitter.

Eric Snowden of Adobe talks about running Adobe applications on the new iPad Pro

Apple hired 65% more women, 50% more African-Americans and 66% more Latinos last year than it did the previous year, the company says.

In the first half of 2015, nearly half of new hires were women, African-Americans, Latinos or Native Americans, according to Apple.

'This represents the largest group of employees we've ever hired from underrepresented groups in a single year' including 11,000 women, Apple CEO Tim Cook wrote in a letter that accompanied the report.

'Some people will read this page and see our progress,' Cook said.

'Others will recognize how much farther we have to go. We see both.'

The firm has even set up a special diversity site to track its progress in the area.

'We believe in equality for everyone, regardless of race, age, gender, gender identity, ethnicity, religion, or sexual orientation,' wrote Tim Cook on the site.

'That applies throughout our company, around the world with no exceptions.'