Merging Path Tracer rendered images to add passes

I just learned that the way the path tracer works, you can add additional passes to a rendered image just by rendering the model again and merging the images.

The path tracer works by randomly applying light for each pass, and if starts with different seeds each time - so it gets different results each time you render, so merging two 100 pass rendered images gives the same quality as a 200 pass image. (More realistically, you might render a scene all night and then decide that you want to give it mores passes, so you can just start a new rendering, and then merge the images.)

Of course, if you haven't closed the renderer yet, you can do the same thing with our "Resume Rendering" Button. But if you have closed the rendering, (or, heaven forbid, if your machine died before it was complete but you have an autosave version), you can just start a new rendering and then merge them together.

When we add this feature to the User Interface, we will need to know how many passes were used for each image, because if you had done 1,000 passes the first time, and wanted to add 500 more, you should blend the images so that the first once is counted 2 X more than the second one.

I rendered two images, just 20 passes each, and attached them here. You can see that they are different. But none of my paint programs will merge them. (I will just have to write my own merge routine) Can someone merge them and post the result? (What we want to see if if merging two 20-pass images gives an equal quality result as making a single 40-pass image)

(A cove light example like this - with just a single upward facing light above the ceiling will look much better with 100s of passes. But it is easier to see the improvement with a 20-pass example like this)

(Also, it you want to use this feature, you will want to work with .PNG images, or .NxtImage images so there is no loss in the images you are merging from .JPG compression)

20 Pass version 1 (also attached)

20 Pass version 2 (also attached)

40 pass version for comparison to merged image

Attachments:

cove 20.png, 533 KB
cove 20B.png, 532 KB

▶ Reply to This

Replies to This Discussion

Permalink Reply by Richcat on October 3, 2011 at 6:17am

Image of merged attachments provided above - done with Merge software(freeware)

If you have the nxtimage files can't you merge them in the nxtimage editor?, but a believe this only works with Path Tracer files.

With the Merge software you could merge Path Tracer and Packet Mode, best of both worlds.

▶ Reply

Permalink Reply by Roy Hirshkowitz on October 3, 2011 at 8:19am

This will work much better with nXtImages. I don't recommend doing this with .pngs. I definitely do not recommending combining Path and Packet tracings-- the results will be very unpredictable.

▶ Reply

Permalink Reply by Render Plus on October 3, 2011 at 8:24am

We will be implementing it in nXtImages as soon as we get the proper toolkit. Except for being precise about the number of passes for each image, and/or if you want to use other nXtImage features on the result, what problems would you anticipate with a PNG image?

There may be cases, e.g. when a render does not complete and you want to use an Autosave file, that you may not have a nXtImage file of the original rendering. (We allow users to save Autosave images in any format they choose - including nXtImage.)

P.S. Here is a 2,000 pass, 3 hour, rendering of the scene for reference: