Você não precisa converter seus arquivos .sub em imagens, o SubResync tem recursos de OCR internos para convertê-los diretamente em texto simples.
De este tutorial a>:
Click open, goto to directory that has your filename.sub
Select your filename.sub by single click then open. By default fps is 25, if your video frames per seconds a different value (23.97, 24, 25. 29.97) select something else.
The subresync dialog box appears...by default "Render" checked and "unlink" not checked. From the "drop down menu" it may detect multiple language options(Eq. 00-Japanese, 01-English, 02-Chinese, 03-Not detected, 04-etc.....)
I only comprehend english so 01 was selected.Then clicked Save As, from the "save as type" drop down menu, select your desired output extension.
Note: OCR Setting "clear image->letter(s) database" will build a database of letters you will be typing. If checked this item will clear the database. Click save to begin.
Follow the moving red box below and "enter matching letter/word/(s)." Once letter is typed press enter. This in turn builds a database of the letter/words/(s) you type. Some times the words don't appear properly cause of unknow character or symbol. Click "extend" to find the remain letter/word/(s).
Finally test your new filenname.srt and see if matches with your flix.