Rendered Channel Information

MAX renders various channels besides the colors you see on the screen. It renders the Object IDs, Material IDs, UVW Map, Normals, Z Depth, and more. This information is useful for post-processing in MAX or in any other external program. These channels are enabled when you render RLA or RPF files.

MAXScript has full access to these channels, allowing us to directly read their information or to read them as grayscale images. Then, you can output these images and use them as masks inside or outside MAX. You can access these channels by rendering an image and asking the renderer to calculate these channels, or by loading an RLA or RPF file.

To render the channels, you need to add channels:#(channel array), where channel array is an array of the channels you want to render. The channels you can list in this array are: #zdepth, #matid, #objectid, #uvcoords, #normal, #unclamped, #coverage, #node, #shadercolor, #shadertransparency, #velocity, and #weight.

To read channel information, use GETCHANNEL, which returns the channel parameters for the specified pixel. This information is extremely technical and differs for each channel. If the bitmap does not have that channel, it will return undefined.

To read the channel information as a grayscale bitmap, you can use GETCHANNELASMASK. The grayscale is similar to the images you see in the VFB when you select these channels. This bitmap can be saved and used anywhere in MAX, or in external post-processing software.

Let’s create a script that will render an image or load a rendered bitmap and will save the channels in separate bitmaps. Open the file render_channel.ms from your CD, or start a new script and type the commands in LISTING 16.5.

 rollout render_channel “Parameters”
 (
 button sel_bmp “Select a Bitmap File” width:150
 button rend_it “Render Image” width:150
 dropdownlist channel “Select Channel” enabled:false width:150 \
 align:#center
 button save_it “Select Bitmap to Save” enabled:false width:150
 fn enable_list bmp =
 (
 if bmp != undefined then
 (
 list_items = #(“RGBA_Channel”)
 if getchannel bmp [0,0] #zdepth != undefined do
 append list_items “Zdepth”
 if getchannel bmp [0,0] #matid != undefined do
 append list_items “MatID”
 if getchannel bmp [0,0] #objectid != undefined do
 append list_items “ObjectID”
 if getchannel bmp [0,0] #uvcoords != undefined do
 append list_items “UVCoords”
 if getchannel bmp [0,0] #normal != undefined do
 append list_items “Normal”
 if getchannel bmp [0,0] #unclamped != undefined do
 append list_items “Unclamped”
 if getchannel bmp [0,0] #coverage != undefined do
 append list_items “Coverage”
 if getchannel bmp [0,0] #node != undefined do
 append list_items “Node”
 if getchannel bmp [0,0] #shadercolor != undefined do
 append list_items “ShaderColor”
 if getchannel bmp [0,0] #shadertransparency != undefined do
 append list_items “ShaderTransparency”
 if getchannel bmp [0,0] #velocity != undefined do
 append list_items “Velocity”
 if getchannel bmp [0,0] #weight != undefined do
 append list_items “Weight”
 channel.items = list_items
 channel.enabled = true
 )
 else
 (
 channel.items = #()
 channel.enabled = false
 )
 )
 on sel_bmp pressed do
 (
 img = undefined
 img = selectbitmap()
 enable_list img
 )
 on rend_it pressed do
 (
 img = render vfb:off channels:#(#zdepth, #matid, #objectid, \
 #uvcoords, #normal, #unclamped, #coverage, #node, #shadercolor, \
 #shadertransparency, #velocity, #weight)
 enable_list img
 )
 on channel selected i do
 (
 execute (“bmp_channel = #” + channel.selected)
 save_it.enabled = true
 )
 on save_it pressed do
 (
 if img2 != undefined then (close img2)
 if bmp_channel == #RGBA_Channel then img2 = copy img
 else img2 = getchannelasmask img bmp_channel
 img2.filename = selectsavebitmap()
 save img2
 display img2
 )
 )
 try (closerolloutfloater channel_floater) catch()
 channel_floater = newrolloutfloater “Render Channel” 200 195
 addrollout render_channel channel_floater

This script uses a new UI item, the listbox. It allows the user to pick one option among several options in a list.

This script allows the user to select or render an image. Then it checks to see which channels exist in this bitmap, and builds a list to be displayed. The user will select the channel they want to save, and can select a bitmap to save it to.

© 2000, Frol (selection, edition, publication)