Review Sony A77: Measurements

26 February 2012

This test report is part of the Sony A77 test. Strengths, weaknesses, conclusions and practice shots are in the Sony A77 review. The measurements for this Sony A77 test report have been carried out with the aid of Imatest. For the test method and explanation of terms, see FAQ.

Resolution of the sensor

jpg-resolutie-Sony-A77

The Sony A77 delivers, with the Sony 16-50 zoom lens, very sharp jpg files. A jpg file has a resolution of more than 2000 LW/PH averaged over all ISO settings in the center. At 3200 ISO, the resolution of a JPG file with 2500 LW/PH is the highest. That is even higher than the resolution of the Canon 5D MK2, a 21 megapixel camera with a full-frame sensor. At the highest ISO setting, ISO 16,000, the noise is so high that the resolution decreases dramatically, both in jpg files (with NR) and RAW files without NR.

Move your mouse over the image for an MTF measurement for the Nikon D700 for comparison.

With a standard editing of the RAW files in Lightroom, an average resolution of nearly 2000 LW/PH is obtained. Slightly lower than the in-camera jpg files thus. This seems remarkable at first sight, since at other cameras like the Canon 5D MK2 or the Nikon D700, the RAW files actually gave a higher resolution than the jpg files. The Sony A77 sharpens the jpg files more than for example the Canon 5D MK2. With Imatest resolution measurements, over sharpening is identified by a bump in black-white transitions, clearly visible in the Sony A77. In the Sony A77 review, we will assess to what extent sharpening is visible to the naked eye.

Dynamic range of the sensor

The with Imatest measured total dynamic range of the sensor varies from 10 stops at 50 ISO, up to 13 stops at higher ISO settings. Much more important than the total dynamic range is the useful dynamic range. A poor signal/noise ratio in the shadow reduces the dynamic range of jpg files to a usable dynamic range of 10 stops at the low ISO settings up to ISO 1600. Then take the usable dynamic range slowly decreases to 0 stops at ISO 16,000. That is a good performance.

The usable dynamic range of RAW files without noise reduction is considerably lower: from 8 stops at 50/100 ISO to 1.6 stops at 1600 ISO.

Through in-camera noise reduction, the jpg files perform at all ISO settings seemingly better than the RAW files. Yet, that is not the case. We test the RAW files without using noise reduction. Accordingly, you maintain the highest possible detail of the shooting, while the noise, although measurable, is not visible in a print. If you carefully optimize contrast, sharpening and noise reduction of RAW files, it is possible to achieve a usable dynamic range for RAW files, which is better or equal to that of the jpg files.

Noise

Comparison of the noise in jpg files with the measured noise in RAW files without noise reduction shows that noise reduction occurs at the jpg files at all ISO settings. In particular from 1600 ISO, the difference in noise of the (by us) unprocessed RAW files without noise reduction and jpg files directly from the camera is visible.

Below are examples of the noise if you would show an unprocessed RAW file without any kind of noise reduction full size on your screen. By applying noise reduction, it is possible to achieve even better results for these RAW files.

The measured values for noise of the Sony A77 are a little lower at ISO 6400 than the measurement results for a RAW file of the Panasonic G3 at ISO 6400. With the naked eye, the difference is difficult to see.

From experience, we know that if the noise is less than 2.5%, a photo can be printed on A3 + size without the noise being seen as disturbing. Based on the above measurement results for noise in jpg files of the Sony A77, you would think that even 16,000 ISO files would yield a beautiful print. In terms of grain size it might be true, but in terms of resolution you have lost a lot of quality at 16,000 ISO. Here, you see a 100% image cropping of a photo of a test card.

Move your mouse over the image to compare 100 ISO with 16000 ISO

Color reproduction daylight

Color reproduction (Delta E 94) Sony A77 in daylight

Average 6.4 (RAW) / 6.8 (jpg)
Best 5.4 (RAW) @ 50 ISO
Worst 7.5 (jpg) @ 16000 ISO
Skin tone: 5.9 (RAW) / 6.7 (jpg)
Natural colors: 5.2 (RAW) / 6.4 (jpg)
Bright colors: 6.0 (RAW) / 6.8 (jpg)

The Sony A77 produces RAW files with good color reproduction for both RAW files and jpg files (neutral) directly from the camera. The color reproduction is also very consistent across all ISO settings. The average measured saturation of RAW files converted in Lightroom is between 108 and 115%. These are not unusual values.

The picture above shows the color errors of an ISO 100 jpg (neutral) image taken in daylight. The further the ideal color (square) is removed from the color reproduction of the camera (round), the greater the color difference. For the test method and explanation of terms, see FAQ.

Color reproduction artificial light

Color reproduction (Delta E 94) Sony A77 in artificial light

Average 8.5 (RAW) / 9.7 (jpg)
Best 7.7 (RAW) @ 50 ISO
Worst 10 (jpg) @ 3200 ISO
Skin tone: 8.4 (RAW) / 10.4 (jpg)
Natural colors: 5.8 (RAW) / 6.7 (jpg)
Bright colors: 7.5 (RAW) / 9.1 (jpg)

The automatic white balance does its job properly at the Sony A77. The color deviation is indeed larger than in daylight shots, but these results are good.

The color reproduction in artificial light can be easily improved with a simple white balance adjustment: The picture above shows the color error of a corrected RAW image taken in artificial light. The further the ideal color (square) is removed from the color reproduction of the camera (round), the greater the color difference.

Move your mouse over the image for a comparison of an ISO 100 taken in artificial light and a for white balance corrected image.

Read more about the Sony A77 in our Sony A77 review.