That's where Astropad comes in. The full version of Astropad lets you use your iPad as a graphics tablet, and now the company just launched a new version of the app for iPhone too.
The new app is called Astropad Mini, and it's going to cost $4.99 as part of its launch promotion on Thursday while the full price will be $9.99.
A graphics tablet is a pressure-sensitive slate that photographers and artists use to easily edit photos on their computers. It allows you to control your computer mouse with a stylus on the tablet so that you can touch up photos with more precision.
So, for instance, if you're editing an image in Photoshop, you'd be able to move the cursor to edit intricate details of the photo using a pen rather than a computer mouse or trackpad.
These tablets are usually pretty expensive, however. High-end graphics tablets, such as those made by Wacom that come with displays, can cost around $1,000.
That's why Matt Ronge and Giovanni Donelli, Astropad's two cofounders who previously worked as engineers at Apple, decided to make something cheaper that would work directly on your iPad. The iPad app debuted earlier this year, but the company said it heard a lot of requests for an iPhone version too.
"It's going to open up access to a lot more people," Ronge told Business Insider.
Like a graphics tablet, Astropad works by connecting your iPhone or iPad to your Mac so that you can mark up images using the touch screen on your iPhone or iPad. And, since the Astropad app mirrors what's on your Mac's screen, you don't have to keep an eye on your Mac's monitor while drawing on the tablet like you would with a cheaper graphics tablet.
Here's a look at what the new Astropad Mini iPhone app looks like:
Ronge also says the user interface has been tweaked in the iPhone version of the app. The team didn't just shrink down the version made for the iPad - it had to "re-think" the entire format and make it simpler since it's designed to work on a smaller screen.
"We had to really boil it down to its essence, what the most important stuff is," he said.
In addition to cutting the app down to its core features, the team also added some new functionality. You can now program shortcuts to work on your Apple Watch. So, for instance, if you wanted to undo an action, you could do so from the Apple Watch rather than finding the submenu in the photo editing program you're using on your Mac.
Ronge is particularly excited about the rumors surrounding Apple's yet-to-be-announced iPhone 6S, which is rumored to come with the same Force Touch technology Apple introduced with the Apple Watch. He thinks a feature such as Force Touch could make an app like Astropad even more useful for photo editors.
"We would have pressure sensitivity right there on the iPhone," he said.