Jump to content
Ultra Engine Community

VicToMeyeZR

Members
 View Profile  See their activity

  • Posts

    570

  • Joined

  • Last visited

 Content Type 

Posts posted by VicToMeyeZR

    DDS Compression Types

    in Game Artwork

    Posted · Edited by VicToMeyeZR

    I think your not looking close enough...

     

    Here, a PSD image, saved as DXT1 no alpha. The bottom is DXT5 No alpha.

     

     

     

    So bottom is DXT5 top is DXT1. Clearly there is a slight difference.

     

    ok, that didn't attach right.

     

     

    preview.jpg

    post-234-12659097303901_thumb.jpg

    DDS Compression Types

    in Game Artwork

    Posted

    No it is not. The second DXT5 image is SOLELY on the RGB channel. I did NOT pull the image from the re-normalize one where they DID use the Alpha Channel.. This is STRAIGHT difference between the DXT1, and DXT5 RGB channels ONLY.

    DDS Compression Types

    in Game Artwork

    Posted

    to quote from that article for your DXT1 question.

    2.1 Object-Space DXT1

     

    DXT1 [3, 4], also known as BC1 in DirectX 10 [5], is a lossy compression format for color textures, with a fixed compression ratio of 8:1. The DXT1 format is designed for real-time decompression in hardware on the graphics card during rendering. DXT1 compression is a form of Block Truncation Coding (BTC) [6] where an image is divided into non-overlapping blocks, and the pixels in each block are quantized to a limited number of values. The color values of pixels in a 4x4 pixel block are approximated with equidistant points on a line through RGB color space. This line is defined by two end-points, and for each pixel in the 4x4 block a 2-bit index is stored to one of the equidistant points on the line. The end-points of the line through color space are quantized to 16-bit 5:6:5 RGB format and either one or two intermediate points are generated through interpolation. The DXT1 format allows a 1-bit alpha channel to be encoded, by switching to a different mode based on the order of the end points, where only one intermediate point is generated and one additional color is specified, which is black and fully transparent.

     

    Although the DXT1 format is designed for color textures this format can also be used to store normal maps. To compress a normal map to DXT1 format, the X, Y and Z components of the normal vectors are mapped to the RGB channels of a color texture. In particular for DXT1 compression each normal vector component is mapped from the range [-1, +1] to the integer range [0, 255]. The DXT1 format is decompressed in hardware during rasterization, and the integer range [0, 255] is mapped to the floating point range [0, 1] in hardware. In a fragment program the range [0, 1] will have to be mapped back to the range [-1, +1] to perform lighting calculations with the normal vectors. The following fragment program shows how this conversion can be implemented using a single instruction.

     

    # input.x = normal.x [0, 1]

    # input.y = normal.y [0, 1]

    # input.z = normal.z [0, 1]

    # input.w = 0

     

    MAD normal, input, 2.0, -1.0

     

    Compressing a normal map to DXT1 format generally results in rather poor quality. There are noticeable blocking and banding artifacts. Only four distinct normal vectors can be encoded per 4x4 block, which is typically not enough to accurately represent all original normal vectors in a block. Because the normals in each block are approximated with equidistance points on a line, it is also impossible to encode four distinct normal vectors per 4x4 block that are all unit-length. Only two normal vectors per 4x4 block can be close to unit-length at a time, and usually a compressor selects a line through vector space which minimizes some error metric, such that, none of the vectors are actually close to unit-length.

    DDS Compression Types

    in Game Artwork

    Posted

    Sorry, I know how to get a dds with an interpolated alpha, my question was if there was a reason to save a texture using DXT5 when you do not want an alpha (such as diffuse textures with no transparency). Josh seemed to be indicating that you should never use DXT1, but I thought the only difference between DXT1 and DXT5 was that DXT5 is able to retain a 4 bpp alpha channel. I did not think there was any difference between DXT1 and DXT5 in terms of RGB channel compression artifacts.

     

    So I have always used DXT1 for textures without alpha channels, and DXT5 for textures with alpha channels. Josh's statement has me wondering if this is the wrong thing to do.

     

     

    What do you mean you don't know how? If you are using the Photoshop plugin, I just told you how. Thats exactly the format I use. It in the drop down box that comes up in Photoshop.

    post-234-12657410690994_thumb.png

    new site

    in General Discussion

    Posted

    Now if you could get a custom page with IP.Board, then you could do away with the "Main" site completely.. Would be better IMO.

     

    I thought they had custom page ability. I could be wrong.

Copyright © 2024 Ultra Software.
All rights reserved.
×
×
  • Create New...