Camera+, an iPhone camera app that has been a top seller in the App Store for years, expanded to the iPad  on Thursday. Not many people shoot photos with an iPad, but the core features of the app are its editing suite and integration of Appleâs iCloud online storage service. The company also released an update for the iPhone version of the camera app to include cloud synchronization, so that photos taken on an iPhone will also appear in the iPad app.
Nine million people so far have downloaded the Camera+ app for iPhone, which costs 99 cents, said Lisa Bettany, a developer at Tap Tap Tap, the studio that made Camera+. Together, the iPad and iPhone apps should pose a challenge to Adobe, which offers a suite of Photoshop apps for editing photos on the iPad, as well as its own cloud storage service.
Like the iPhone version, the iPad app was designed to make editing photos quick and easy. It has five basic tools: Scenes for applying automatic touch-ups for photos taken in certain light conditions, like in low light or indoor areas; Adjust for making basic adjustments like rotating the image or removing red eye; Crops for cropping portions of a photo; FX Effects for applying fancy filters; and Borders for adding stylized borders.
In addition to allowing photos taken on an iPhone to automatically appear in the Camera+ iPad app, the company has designed the iPad app to allow photos edited in that app to synchronize automatically with the userâs iPhone photo library. Sharing the photos on Facebook, Twitter and Flickr, or through e-mail, can be done inside the apps.
Ms. Bettany said it was extremely challenging to make iCloud work properly inside the app. She said that Appleâs toolkit for embedding iCloud was inadequate on its own, and that her team had to retool the feature to get it to work.
âIt didnât work for the past year, and developers have been complaining about how bad it is,â Ms. Bettany said in an interview. âOur developers have recoded the whole thing to make it work. Itâs taken twice as long as it should because of the problems with it.â
Trudy Muller, an Apple spokeswoman, declined to comment.
Tap Tap Tap  , which has sold a number of big hits in the App Store, is an unusual success story. To attract early sales for new apps, it sends an e-mail to its list of about 325,000 past customers who opted to gets e-mails from the company, many of whom enthusiastically download the apps. After getting a big spike in sales, the company then relies on the quality of the app to generate word-of-mouth. It does no traditional advertising and does not take money from investors. At one point it turned away Twitter  , which was interested in acquiring Camera+.
Ms. Bettany said the company has carefully studied the economics of the App Store, but even she is surprised that Camera+ has lasted so long as a top seller with so many apps competing for peopleâs downloads.
âSometimes Iâm baffled, like, why are we still here?â she said. âBut it just comes down to it being a good product. Even though apps come along â" and Iâll admit when an app does things better than us â" it seems like our app is the most stable, has the least bugs, it works consistently, itâs easy to use, itâs not too complex and it doesnât have too many buttons.â