Color Accuracy
Detailed analysis of the Nikon Coolpix 4800 images, from Imatest(tm)
**YAZMIN - this page should probably really be put into the standard template, and the backlinks to the review at the top should probably have some more appealing treatment as well, use your own judgement. - Note though, that the charts are as large as 680pix wide, don't know if that'd cause you any problems.**
(Back to Coolpix 4800 review, back to Coolpix 4800 picture-analysis page)
I've recently begun using Norman Koren's excellent "Imatest" analysis program for quantitative, thoroughly objective analysis of digicam test images. I highly commend it to our technically-oriented readers, as it's far and away the best, most comprehensive analysis program I've found to date. (And with an introductory price of only $59, it's hard to beat.)
My comments below are just brief observations of what I see in the Imatest results. A full discussion of all the data Imatest produces is really beyond the scope of this review: Visit the Imatest web site for a full discussion of what the program measures, how it performs its computations, and how to interpret its output.
Here's some of the results produced by Imatest for the Nikon Coolpix 4800:
Color Accuracy
Overall, the Coolpix 4800 has pretty good hue accuracy, but like many consumer-level digicams, tends to oversaturate its colors a fair bit. Oversaturation is worse with strong reds, greens, and blues, but is quite low with more pastel hues. (Accounting for the Coolpix 4800's generally good skin tones.) The oversaturation is shown by the extent to which the circles (camera color) are displaced outward (higher saturation) relative to the ideal values (squares). On average, color saturation of swatches on the MacBeth ColorChecker(tm) chart are 117.7% of their ideal values. (An average oversaturation of 17.7%.)
Color Analysis
These images show the color behavior of the Coolpix 4800 directly. In each color swatch, the outer perimeter shows the color as actually captured by the camera, the inner square shows the color after correcting for the luminance of the photographed chart (as determined by a 2nd-order curve fit to the values of the gray swatches), and the small rectangle inside the inner square shows what the color should actually be, based on perfect rendering to the sRGB color space.
Here, it seems that at least some of the oversaturation arises from the camera's rather contrasty tone curve.
Gray Patch Tone and Noise Analysis
There's a lot in this particular graph, a lot more than I have room to go into here. Bottom line, the Coolpix 4800's noise levels are average to a little higher than average at low ISO values, but the noise pattern is a little coarse.
This chart compares the Coolpix 4800's noise performance over a range of ISOs against that of other cameras. As you can see, the Coolpix 4800 is slightly noisier than average at low ISOs, but noise levels take a sharp jump upward at ISO 400.
The chart above shows consolidated results from spatial frequency response measurements in both the horizontal and vertical axes. The "MTF 50" numbers tend to correlate best with visual perceptions of sharpness, so those are what I focus on here. The uncorrected resolution figures 1188 line widths per picture height in the horizontal direction (corresponding to the vertically-oriented edge), and 1265 along the vertical axis (corresponding to the horizontally-oriented edge), for a combined average of 1227 LW/PH. Correcting to a "standardized" sharpening with a one-pixel radius drops this number slightly, to an average of 1219 LW/PH. A good performance, consistent with the Coolpix 4800's 4-megapixel resolution level.
For the real techno-geeks, the two plots below show the actual edge response of the Coolpix 4800, for horizontal and vertical edges:
