使用Prawn添加图像，出现错误：Prawn :: Errors :: UnsupportedImageType，PNG使用不受支持的交错方法(Add image using Prawn, got error: Prawn::Errors::UnsupportedImageType, PNG uses unsupported interlace method)

 我使用Prawn来创建PDF文件，我想把文件放在文件中。 我已经看过这个网站创建pdf来引用如何添加图像。 
 
 这是我在ExamResultPdf.rb文件中生成pdf的代码： 
 
  def initialize(exam, view)
    super(top_margin: 70)
    @exam = exam
    exam_number # line 9, I removed codes are not relevant
  end

  def exam_number
    logo_path = "#{Rails.root}/app/assets/images/logo_hoasen.png"
    image logo_path, height: 200, width: 200
    text "Examination Result \##{@exam.id}", size: 30, style: :bold
  end
 
 但是当我去页面/result.pdf ，它有错误： 
 
Prawn::Errors::UnsupportedImageType in ExamsController#result
PNG uses unsupported interlace method

# Trace
app/pdfs/exam_result_pdf.rb:18:in `exam_number'
app/pdfs/exam_result_pdf.rb:9:in `initialize'
app/controllers/exams_controller.rb:43:in `new'
app/controllers/exams_controller.rb:43:in `block (2 levels) in result'
app/controllers/exams_controller.rb:40:in `result'
 
 我的exams_controller ： 
 
def result
    @exam = Exam.find(params[:id])
    @general_exam = GeneralExam.where(id: @exam.general_exam_id).first
    @topic_questions = TopicQuestion.where(general_exam_id: @general_exam.id)
    @exam_result = ExamResult.where(exam_id: @exam.id, user_id: @exam.user_id).first

    respond_to do |format|
      format.html
      format.pdf do
        pdf = ExamResultPdf.new(@exam, view_context) # line 43
        send_data pdf.render, filename: "exam_result_#{@exam.id}",
                                  type: "application/pdf",
                           disposition: "inline"
      end
    end
  end
 
 所以我想问为什么我得到这个错误，Prawn不支持png文件？ 我怎样才能把图像放在pdf文件中？ 
 
 更新 
 
 我使用过jpg或jpeg文件，但它也没有用。 

I used Prawn to create pdf file, I want to put the logo in file. I have looked at this site Creating pdf to reference how to add image.
 
This is my code in ExamResultPdf.rb file to generate pdf:
 
  def initialize(exam, view)
    super(top_margin: 70)
    @exam = exam
    exam_number # line 9, I removed codes are not relevant
  end

  def exam_number
    logo_path = "#{Rails.root}/app/assets/images/logo_hoasen.png"
    image logo_path, height: 200, width: 200
    text "Examination Result \##{@exam.id}", size: 30, style: :bold
  end
 
But when I go to page /result.pdf, it has error:
 
Prawn::Errors::UnsupportedImageType in ExamsController#result
PNG uses unsupported interlace method

# Trace
app/pdfs/exam_result_pdf.rb:18:in `exam_number'
app/pdfs/exam_result_pdf.rb:9:in `initialize'
app/controllers/exams_controller.rb:43:in `new'
app/controllers/exams_controller.rb:43:in `block (2 levels) in result'
app/controllers/exams_controller.rb:40:in `result'
 
My exams_controller:
 
def result
    @exam = Exam.find(params[:id])
    @general_exam = GeneralExam.where(id: @exam.general_exam_id).first
    @topic_questions = TopicQuestion.where(general_exam_id: @general_exam.id)
    @exam_result = ExamResult.where(exam_id: @exam.id, user_id: @exam.user_id).first

    respond_to do |format|
      format.html
      format.pdf do
        pdf = ExamResultPdf.new(@exam, view_context) # line 43
        send_data pdf.render, filename: "exam_result_#{@exam.id}",
                                  type: "application/pdf",
                           disposition: "inline"
      end
    end
  end
 
So I want to ask why I got this error, Prawn is not support png file? How can I put image in pdf file? 
 
Update
 
I have used jpg or jpeg file, but it did not work too.

原文：https://stackoverflow.com/questions/13741110