A developer’s explanation of the iPad’s photo editing limitations

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Back when I did the TouchUp review someone asked if it was able to edit high resolution images. I checked, and found out that 3mpix was the limit. I tweeted the developer about this and a couple of tweets and an email later I had a very thorough and very interesting explanation in my inbox. Read on to see the gist of what I was told by the TouchUp developers.

There are several reasons why TouchUp is unable to edit photos larger than 3mpix while other apps can stitch together 18mpix panoramas or edit 720p, according to the TouchUp developers. First off you have the fact that both the panorama app and video editing app only keeps thumbnails in memory and finalize the end result by rendering, which isn’t exactly real time. Photo editing like TouchUp where you work with details require the full resolution image, which means you need to be able to do it real-time or compromise:

“For us, it was very important to be able to allow a user to zoom in at any time and work on individual pixels of an image in TouchUp. We would not be able to do this if the application worked on a lower resolution proxy to fit into the memory space available.”

A second issue is that TouchUp is designed to use the GPU, not the CPU. Unfortunately the iPad’s GPU can’t work with textures (single images) more than 2048×2048 pixels:

“There are two hardware limitations that effect our app, TouchUp. First the graphics processor (GPU) in the current iPad has a hard limit of working with a single chunk of image data that is 2048 x 2048 pixels. This is the immediate reason that we scale any images larger than that size down when starting a new document.”

This has hopefully been increased in the iPad 2, along with the GPU performance:

“[W]e are now in a position to benefit from the frequently dramatic increases in GPU power as the iPad evolves. For instance, the iPad 2 announced today has the potential of up to 9x’s the GPU performance of the first iPad according to Apple’s marketing materials. The CPU performance enhancement of iPad 2 is unknown, but is probably in the neighborhood of 2 times the current model.”

“We don’t know just yet, but there is also a good chance that the maximum texture size has increased with iPad 2 as well. If this is true we will be able to make quick changes to TouchUp to increase the maximum image size on newer iPads.”

This is excellent news assuming that the texture limit has been raised. Add a 9x GPU performance jump to that and you have the recipe for some serious increase in what TouchUp can do.

RAM is another problem they mention in the email, and that is something every iPad owner is painfully aware of- with only 256MB of RAM in the iPad 1 and half of it being used by the system, there really isn’t much left. Aside from just lack of RAM, they also point out a problem with photo editing and RAM that I wasn’t aware of:

“Consider that a 10MP image is around 40Mb when decompressed in memory. 2 of those and you’ve likely used up all the RAM in the first generation iPad without anything left over for the rest of your program.”

“The TouchUp engine works such that we have nearly unlimited layers of effects. Each layer blends the effect back into the result of the layers beneath it and all of this is done non-destructively so you can revert your edits and draw and erase the effects at will. This is all very powerful, and we think novel for iPad, but it requires holding several images sized the same as the original in memory at once.”

“You may find that other photo editing applications have the ability to work on slightly larger images (some in the 10MP range), but I don’t believe you will find any of them have the same sort of power in the non-destructive brushing and blending engine we have in TouchUp”

In other words, having a nondestructive photo editing app that doesn’t apply the effects to the photo permanently but preserves it as a backup means that you need more RAM than the iPad 1 is able to provide. I think that nondestructive editing is an excellent feature especially when you’re working with several layers of effects, so I hope the iPad 2 will let them “run wild” with higher resolution images without having to compromise on that feature. Of course, if the iPad 2 doesn’t get more RAM, we’re pretty much screwed, but I hope that Apple isn’t that dumb. 512MB is likely, 1GB if they really like us, and the same 256MB only if Steve Jobs has become a drunk.

It was very nice of Chris at TouchUp to give us such an amazingly detailed answer to why the app is limited the way it is. It makes a lot of sense and it’s a wake up call in regards to how limited these tablets still are performance wise, even if they can do some things very well. This year we have major improvements and next year will no doubt see the same type of performance increase from this year’s tablets so I’m really excited to see what sort of photo editing apps we will have then. The day that I have a fully working version of Photoshop and Camera RAW on my iPad is going to be the day I stop buying new versions of tablets as that will be the day that performance has reached a point where further increases are practically pointless to me, but until then I’ll by using apps like TouchUp for all they’re worth and I can’t wait to see an iPad 2 version of that app.

Here’s another link to the review in case you want to check out TouchUp, having developers that are open about these things is a reason to buy the app itself. Quite a different reply than when I contacted Circus Ponies and asked for a comment on what makes their note taking app better than smartNote which is 1/10 the price. Never got a response on that one, so I guess that pretty much answers the question as well.


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Andreas Ødegård

Andreas Ødegård is more interested in aftermarket (and user created) software and hardware than chasing the latest gadgets. His day job as a teacher keeps him interested in education tech and takes up most of his time.

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