Search in
Sort by:

Question Status:

Search help

  • Simple searches use one or more words. Separate the words with spaces (cat dog) to search cat,dog or both. Separate the words with plus signs (cat +dog) to search for items that may contain cat but must contain dog.
  • You can further refine your search on the search results page, where you can search by keywords, author, topic. These can be combined with each other. Examples
    • cat dog --matches anything with cat,dog or both
    • cat +dog --searches for cat +dog where dog is a mandatory term
    • cat -dog -- searches for cat excluding any result containing dog
    • [cats] —will restrict your search to results with topic named "cats"
    • [cats] [dogs] —will restrict your search to results with both topics, "cats", and "dogs"

Lightmap RGBA Channels breakdown?

Does anyone know what each channel represents within the Lightmap RGBA? I assume that RGB is used for GI luminosity and Color but what about the Alpha channel? Is that AO? How does Lightmass use these channels?

I have enclosed two views of the test mesh level, the original (uncompressed) HG_Lightmap and its RED channel and ALPHA channel.

@DanielW would you be so kind as to explain this to us and what the banding portion in the Alpha is use for?

alt text alt text alt text

alt text

alt text

Product Version: UE 4.11
hq_lightmap.jpg (79.4 kB)
hq_lightmapr.jpg (55.2 kB)
hq_lightmapa.jpg (81.6 kB)
boxtest01.jpg (32.7 kB)
more ▼

asked Apr 29 '16 at 05:54 PM in Rendering

avatar image

91 8 13 23

avatar image Haskellf Aug 16 '16 at 01:16 AM

I'd still like to hear from Staff in regards to the Lightmap channel breakdown.

(comments are locked)
10|2000 characters needed characters left
Viewable by all users

1 answer: sort voted first

Hi there,

I was also wondering about this and I made a question on the Developer network. someone from the staff replied so it might be useful to check this out! https://udn.unrealengine.com/questions/352364/lightmap-rgba-channel-breakdown.html

more ▼

answered Mar 23 '17 at 09:13 AM

avatar image

6 1 1

avatar image Haskellf Mar 23 '17 at 03:46 PM

Thanks for the response. Unfortunately, I am unable to gain access to the link because I am not part of technology developers program. Could you cut and paste the information from that link response to here? That would be most helpful. Thanks!

avatar image Sander74 Mar 23 '17 at 03:50 PM


For lightmaps the engine uses 2 samples from the same texture:

Sample0.a and Sample1.a encodes the precomputed lighting HDR luminance.

Sample0.rgb encodes the precomputed lighting color.

Sample1.rgb encodes the directional scale factors.

The HDR luminance data is only encoded when using HQ lightmaps (see "r.HighQualityLightMaps"). This doubles the lightmap sizes but allows smooth gradients and wider range support.

You can look at how the channels are used in LightmapCommon.usf if you want the details.

For shadowmaps, the engine encodes 1 light shadow attenuation per channel, supporting up to 4 precomputed shadows per mesh.

(comments are locked)
10|2000 characters needed characters left
Viewable by all users
Your answer
toggle preview:

Up to 5 attachments (including images) can be used with a maximum of 5.2 MB each and 5.2 MB total.

Follow this question

Once you sign in you will be able to subscribe for any updates here

Answers to this question