Cutout Service

[asd das]

Dear DECaLS Support Team,尊敬的贴花支持团队：

 I am writing to clarify a couple of questions regarding the DECaLS DR10 cutout service and the properties of the FITS files it provides.我写这封信是为了澄清关于DECaLS DR10切割服务及其提供的FITS文件属性的几个问题。

1. Cutout Service and Coadd Data:切割服务和编码数据：
   

   Could you please confirm whether the images provided through the cutout service are directly extracted from the coadded data products available in DR10? I want to ensure that the cutout images reflect the same processing and quality as the coadd images used in the survey’s data release.请确认通过切割服务提供的图像是否直接从DR10中可用的编码数据产品中提取？我想确保切割图像反映出与调查数据发布中使用的代码图像相同的处理和质量。

2. Negative Pixel Values in Single-Band FITS:负像素值在单波段FITS：
   

   I noticed that some of the single-band FITS images downloaded through the cutout service contain negative pixel values. I am curious whether this is expected and if it results from an automated background subtraction applied during the cutout process. If background subtraction is involved, could you please provide more details on how it is performed?我注意到通过切割服务下载的一些单波段FITS图像包含负像素值。我很好奇这是否是预期的，如果它是在切割过程中应用的自动背景减法的结果。如果涉及背景减法，能否提供更多细节？

Your insights will be very helpful for my research. Thank you for your time and support. I look forward to your response.
thanks!
Chen你的见解对我的研究很有帮助。感谢您的时间和支持。期待您的回复。

[Dustin Lang]

Hi,

Images from the cutout service are resampled from the DR coadded images.  If you request the original pixel scale (0.262"/pix), then the cutout images contain the same information as the DR.

A cutout may include data from multiple "bricks" from the DR, and they are resampled for the pixel grid you have requested.

Negative pixel values are expected, because we have done a sky subtraction step.  This is described in the Dey+2019 overview paper.

cheers,

dustin

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