Canon Digital Rebel Color Resolution Tests

Page last edited Nov 19, 2005, 1:45 pm PST

The following images were shot to evaluate the effective resolution of a Canon Digital Rebel camera (3072 x 2048 pixels) when dealing with single-color light. 

Major result: There is a slight resolution loss for green light as opposed to white, but a significant loss for red and blue. 

However, the nature of the resolution loss is more like blurring than the block effect described at and illustrated in the links at .  Presumably this is due to differences in the raw-to-RGB conversion algorithm.

Just for context, here is the full-frame view with no filters.  We're going to look at the small block in the center of the resolution chart.

All of the following images have been blown up to 400% with nearest-neighbor interpolation in Photoshop. 
The inset at lower right is the same image at actual pixels (100%).

Here is the central portion of the resolution chart.  The order is 1) no filter, 2) #29 red, 3) #61 green, and 4) #47B blue.


To illustrate the effect of Sharpness and Color Noise Reduction settings, here are two no-filter images.  On the left is with default settings (Sharpness=25, Color Noise Reduction = 25); on the right is with Sharpness=0, Color Noise Reduction = 0, same as shown above.


Tiff downloads:
NoFilter Options0 Image.tif
NoFilter OptionsDefault Image.tif

Update Nov 18, 2005:

The raw-format CRW files were processed through dcraw ( using the -d parameter to extract raw sensor data (no de-Bayering, no interpolation).  The resulting files clearly show what appears to be the Bayer filter pattern.  Here is the dcraw -d output for the red, green, and blue filters, applied as a Photoshop layer mask against uniform red, green, and blue tones to help visualize them.


Notice that the green filter produces significant response at all sensor positions. 

Numerically, the responses in the upper-left Bayer quad are:

           Bayer Filter Position
in front
of lens

68 181

These values are after conversion by IrfanView from dcraw's -d ppm output to 8-bits-per-color tiff.  They may or may not represent actual sensor values, but should give an idea of relative responsiveness.