This color image combines many exposures from Hubble Space Telescope's Advanced Camera for Surveys (ACS) and Cerro-Tololo Interamerican Observatory's (CTIO) 4m Blanco Telescope and MOSAIC2 camera.
HST/ACS image of Halpha Carina Nebula
96 ACS exposures covering 48 separate, overlapping fields were made with a filter transmitting the light of neutral hydrogen (H-alpha). These combine to form a mosaic image of roughly 400 megapixels (0".05/pixel) spanning about 13x26 arcminutes on the sky.
Images from CTIO were made using three narrow band filters: doubly ionized oxygen ([O III] 501nm), neutral hydrogen and singly ionized nitrogen (H-alpha+[N II] 658nm) and singly ionized sulfur ([S II] 672+673nm). These were combined into a color composite image, assigning blue to nitrogen, green to hydrogen and red to sulfur.
CTIO Ground-based Image of Carina Nebula (courtesy of N. Smith)
The higher resolution, black & white Hubble image and the lower resolution, color CTIO images were combined using a technique that takes luminosity (brightness) information from the black and white ACS image and color information from the composite CTIO image. This preserves all of the higher-resolution detail from the Hubble data while rendering a color image representing the physical processes in this active region of space.
A few small gaps in the mosaic of ACS images were replaced by sections of the matching CTIO hydrogen-light image. Other sections of the image were bright enough to "saturate" the camera detector. (All of the pixels in a given region of the image are at their maximum numerical value resulting in total white patch.) The saturated area around the brightest star in the field, Eta Carinae, were replaced with images from previous shorter exposures from Hubble's Wide Field Planetary Camera 2.