Highlights:

The HOYA color correction filters, BLUE COOLING and UMBER WARMING, are designed to adjust the white balance of the image.

The UMBER WARMING series corrects blue cast caused by cool lighting conditions, especially in shadowy areas, by adding a red/orange tint to the image. Typical conditions are overcast days or shady conditions. Since UMBER WARMING filters add a warmth to pale skin tones, they are especially ideal for portrait shots.

Technology

The UMBER WARMING series features W2, W4, W10 and W12 gradation, which refer respectively to a mired shift of +20, +40, +100 and +120.

In other words, as seen in the transmission graph, the UMBER WARMING series reduces blueish and greenish light entering the lens, therefore indirectly enhancing yellow and red colors. The higher the mired value, the less blue and green light enters the lens and the stronger the warming effect.

It is possible to combine various UMBER WARMING filters to achieve different values, which allows photographers to achieve almost any desired color correction.