8/24/2023 0 Comments Substance alchemist normal map![]() The other Basis formats are native to most Apple products, but aren’t great for non-color data. BCn requires Direct3D 11 support and on the Mac is only available in devices that support Metal. There is one last consideration, however, and that is compatibility. But you will need to create custom shaders to handle them. However, specifically for normal maps, BC5 compression of a 2 channel normal texture (or another 2-channel data packed texture) will be best as both channels are compressed separately. however, the drawback is that mode 6 of BC7 links the color channels and alpha channel so there will be some cross-talk, but the support of multiple color space lines per block will reduce some of the artifacts that will be present with cross talk. This happens commonly in normal textures, so any format that only supports one color space line per block is a non-starter for normal textures.īC7, however, supports multiple color space lines per block, so it can support widely changing color pixels within the same block. if you have more than 2 color hues represented within the block that don’t fit on the color space line, they will be changed to colors that appear on the line. This is problematic when there are hard shifts in color within the block, i.e. ![]() The reason is that most of the BCn methods will use a single color space line per block to determine what colors are represented by each pixel as a position along the line defined by two end points in the block. The BC7 (mode 6) option, while meant for HDRI compression, could be used for non-color data that needs more than 2 channels. That format wouldn’t work for a three or four channel data-pack, however so there is only one other BCn format that may work. You can, however, create your own shader with node material to support this kind of normal texture format. The drawback here is that we have not implemented support for 2-channel normal textures in our standard materials yet as there has not been a lot of call for it. They are compressed separately from one another, so you can use RG normal maps and calculate the B channel in your shader. BC5 is designed for normal maps, but only takes two channels as greyscale. The remaining option is BCn which has a couple of options. Of the basis formats, PVRTC1 and ETC1/ETC2 will perform similarly to ETC1s in that you will have a lot of artifacts to deal with in non-color data. But from our tests, using ETC1s for non-color data like a normal map produces very poor results so the smaller footprint in memory isn’t actually worth it. For non-color data UASTC does a good job of eliminating the artifacts you will see in ETC1s at the cost of a larger size in memory. Through our internal testing of KTX, we have determined that for color data using the ETC1s gives the best combination of file size with an acceptable level of artifacts, mostly in areas of hard color transition. The ETC1s mode will create a smaller file for KTX, but again is subject to cross talk in its compression, so is not a good candidate for non-color the question about texture compression isn’t straight forward as there are many different considerations you need to entertain to choose the correct format. If you are running into size problems with your files, you can use KTX compression using the UASTC mode which does compress without cross talk. To prevent this, you will want to use a PNG format for any non-color data files (roughness, metallic, normal, etc). This will lead to artifacts in the individual maps that are not explainable since the file format assumed all three channels would be displayed together and not separated like channel packing would do. In essence, the compression is looking at the composite of the R, G, and B channels to determine what values to write into the file, which means that each map is being changed based on data in the other channels. The reason this is problematic with non-color data and especially with channel packed textures is that jpg block compression is subject to cross talk between the channels. There is one problem that I see from the uploaded image, however, though it may have been due to the upload, but the image you shared is a jpg format file.
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